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The ferromagnetic properties of hematite

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THE FERROMAGNETIC PROPERTIES OF HEMATITE
By
E a rl Thoms Hayes
0e>p
T hesis su b m itted to th e F a c u lty o f th e G raduate School
of th e U n iv e rs ity o f Maryland in p a r t i a l
f u lf illm e n t o f th e req u irem en ts f o r th e
degree o f D octor o f P hilosophy
194-0
UMI Number: DP70141
All rights reserved
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ACIOTOEDGMENTS
This work was done under th e a u sp ic e s of th e Chemical
E ngineering D epartm ent, U n iv e rs ity of M aryland, D r, W ilb e rt J ,
H uff, Chairman, whom th e a u th o r w ishes to thank f o r sym pathetic co­
o p e ra tio n .
The problem was su g g ested by Dr. E. S. Dean, C hief E n g in eer,
M e ta llu rg ic a l D iv is io n , U. S. Bureau o f M ines, who p ro v id ed la b o ra to ry
space and f a c i l i t i e s f o r th e e x p erim en tal s tu d ie s in v o lv e d .
The w r ite r
w ishes to ex p ress h is g r a titu d e to D r. V. H. G o ttsc h a lk , S e n io r P h y si­
c i s t , M e ta llu r g ic a l D iv is io n , U. S. Bureau o f M ines, whose numerous
su g g e stio n s and p a tie n t te a c h in g s were in v a lu a b le in c a rry in g out t h i s
work.
The w r ite r i s a lso in d e b te d to D r. B. A. Rogers and Mr. K.
0 . Stamm, M e ta llu rg ic a l D iv is io n , U. S. Bureau o f M ines, f o r th e use
o f t h e i r m agnetic b a lan c e f o r therm om agnetic m easurem ents; and to Mr.
Edward A. Separk, O liv e r Iro n M ining C o., f o r fu rn is h in g sam ples o f
h e m a tite .
TABLE OF CONTENTS
Page
INTRODUCTION
LITERATURE
.........................................................................
.
1
...........................................................
4
GENERAL CONSIDERATIONS.........................................................................
10
H y s t e r e s i s .....................
10
N o m e n c la tu re .........................
11
MATERIAL USED
......................................................................................
12
.....................
R a r ity o f h e m a tite s
12
Source and a n aly se s o f h e m a t i t e .......................................
THEORY
13
...................................................................................
Fundamental e q u atio n
15
....................................................
Measurements based
on th e
d i f f e r e n t i a l e q u atio n
Measurements based
on th e
in te g r a te d eq u atio n
. . 16
. . . 18
EXPERIMENTAL..........................................................................................
A pparatus
15
* • • * •
20
20
C a lib ra tio n
.....................
22
Procedure
......................................
27
L im ita tio n s o f proced u re
...................................................
29
Sample c o m p u ta tio n ....................................................................
R e s u lts
. . . . . .
......................
29
30
DISCUSSION OF RESULTS..............................................................
S u s c e p ti b ility
49
................................................................
H y ste re s is loops • • • . .
••
R e m a n e n c e ..........................................................................................
49
51
53
TABLE OF CONTENTS ( c o n t . )
Page
C oercive fo r c e
♦ .................
54
Thermomagnetic
. . . .............................................................
57
M agnetic s e p a ra tio n p o s s i b i l i t i e s
..............................
59
CONCLUSIONS........................................................................................
61
INTRODUCTION
The problem o f b e n e f ic ia tin g American ir o n o re s i s n o t a new
one and may be expected to become in c re a s in g ly im p o rtan t w ith tim e .
R eserves i n th e U nited S ta te s i n May 1938'*" amounted to ap p ro x im ately
1,400*000,000 to n s .
W ith a y e a r ly p ro d u c tio n o f 50,000,000 to n s t h i s
co u n try has an a s s u re d p ro d u c tio n f o r o n ly 25 o r 30 y e a r s .
This f ig u r e
does n o t appear alarm ing u n t i l i t i s c o n sid e re d t h a t th e average grade
of th e re s e rv e s i s tre n d in g downwards vdiile th e b l a s t fu rn a c e o p e ra to r
s t i l l demands t h a t th e grade of th e incoming ore be a t l e a s t 50 p e rc e n t
ir o n .
Even now mine o p e ra to rs a re mixing le a n o res w ith r ic h o re s to
hold th e grade to about 51 p e rc e n t and conserve th e h ig h -g rad e d e p o s its .
O bviously, when th e grade o f ir o n o re produced f a l l s under t h i s f ig u r e
th e r e w i l l be an in c re a s e in th e p r ic e of p ig ir o n and a corresponding
i n d u s t r i a l re a d ju stm en t in p r ic e f o r a l l f in is h e d ir o n p ro d u c ts .
There a re immense d e p o s its of m arg in al o re s —30 to 50 p e rc e n t
ir o n —i n t h i s c o u n tiy . I f some cheap method o f c o n c e n tra tin g th e s e o re s
2
could be found th e U nited S ta te s would be a ssu re d o f ir o n supremacy f o r
p r a c t i c a l l y an in d e f i n i t e p e rio d .
I t must be borne in mind t h a t any con­
c e n tr a tio n p ro c e ss developed must be cheap, e f f i c i e n t , and capable of
h a n d lin g la r g e tonnages because th e i n i t i a l v alu e o f th e ir o n o re
u s u a lly
$3
p e r to n o r l e s s .
is
About 15 p e rc en t o f our t o t a l y e a r ly p ro ­
d u c tio n comes from th e b e n e f ic ia tio n o f c e r ta i n ir o n o r e s , m ainly by
g r a v ity m ethods, such a s lo g w ashing and jig g in g .
The la r g e tonnage o f
U n ited S ta te s Bureau of Mines M inerals Yearbook, 1939* s e c tio n on
ir o n ore p ro d u c tio n .
^ Ir o n ore c o n c e n tra tio n p ro c e sse s a re p r in c i p a l ly d ir e c te d tow ards
removing th e g r e a te s t im p u rity , s i l i c a ; l i t t l e can be done i n changing
th e phosphorus o r s u lf u r c o n te n t.
2
ir o n r e je c te d by th e s e methods le a v e s much to be d e s ire d from th e
m e ta llu r g ic a l sta n d p o in t o f p e rc e n t re c o v ere d .
F lo ta tio n ^ has been
t r i e d on th e s e w ash-ore t a i l i n g s , b u t i t can h a rd ly be s a id t h a t i t
h as p ro g re s se d to th e s ta g e o f commercial a p p lic a tio n .
Of l a t e , a
s in k and f l o a t p ro c e ss has shorn in te r e s t in g p o s s i b i l i t i e s , b u t s u f f i ­
c ie n t tonnage has n o t been h andled as y e t to e s ta b li s h th e method.
During th e l a s t few y e a rs a p r o c e s s ^ ^ has been developed on th e Mes a b i Range f o r r o a s tin g th e h e m atite in a red u cin g atm ospheieto p ro ­
duce m a g n e tite , and th e n c o n c e n tra tin g t h i s on an o rd in a ry d i r e c t c u r­
r e n t m agnetic s e p a ra to r.
The hig h c o st of reducing th e ore and
subsequent b r iq u e ttin g o f th e c o n c e n tra te s r e s t r i c t th e use o f t h i s
method to s e le c te d c a s e s .
In 1922, Mordey^ d isco v e re d a new a c tio n
o f a lte r n a t in g m agnetic f i e l d s on ferro m ag n etic m a te ria ls —new in
re s p e c t to th e f a c t t h a t th e r e was a re p u ls io n of m a te ria l from a l ­
te r n a tin g m agnetic p o le s as w e ll as an a t t r a c t i o n .
This o f f e r s a po­
t e n t i a l means f o r c o n c e n tra tin g h e m atite o re s a t a low c o st p e r to n .
In o rd e r to develop t h i s id e a p r a c t i c a l l y , a knowledge of th e m agnetic
p r o p e r tie s o f h e m a tite i s in d is p e n s a b le .
^ John N. S e a rle s . Some T e sts w ith F lo ta tio n on Mesabi Wash Ore
T a ilin g s . Eng. and Min. J o u r ., 1939, n o . 6 , 1933, pp. 42-44*
^ E. W. D avis. F i r s t M agnetic R oasting P la n t in th e Lake S u p erio r
R egion. Amer. I n s t . Min. and Met. E ng., Tech. Pub. 731, 1937.
5 J . J . C ra ig . M agnetic C o n cen tratio n on th e Mesabi Makes P ro g re ss .
Eng. and Min. J o u r ., 139, no. 1 , 1933, pp. 43-52,
r
W. W. Mordey. The C o n cen tratio n o f M inerals by Means o f A lte r ­
n a tin g E l e c tr ic C u rre n t. Min. Mag., 26, 1922, pp. 333-343.
3
As our knowledge of th e m agnetic p r o p e r tie s o f h e m a tite was
frag m e n ta ry and w holly in a d eq u a te f o r th e purpose i n view , i t was e s s e n t i a l t o determ ine th e h y s te r e t i c c o n sta n ts
7
o f h e m a tite .
T his was
th e o b je c t o f th e work d e sc rib e d in t h i s p a p e r.
7
The h y s te r e ti c c o n sta n ts a re c o e rc iv e fo rc e and remanence which
we s h a l l c o n sid e r as c h a r a c t e r i s t i c e x c lu s iv e ly of fe rro m ag n e tic sub­
s ta n c e s .
u
LITERATURE
A lthough many in v e s tig a to r s have worked w ith n a tu r a l and
a r t i f i c i a l f e r r i c oxide (Fe203 ) , o n ly a few have reco g n ized th e tr u e
fe rro m a g n e tic n a tu re o f h e m a tite w h ile many have a s c rib e d th e f e r r o ­
m agnetic e f f e c t s to th e p re sen c e o f gamma h e m a tite o r “fe rro m ag n e tic
f e r r i c ox id e11•
8
I t i s tr u e t h a t th e c r y s t a l of h e m a tite has p re f e r r e d
p la n e s o f m agnetization*
9
b u t t h a t f a c t has l i t t l e b e arin g on th e
p re s e n t problem because most h e m atites a re p o ly c r y s ta l lin e and f o r
p urposes of m agnetic s e p a ra tio n only a knowledge o f t o t a l m agnetiza­
t i o n i s necessary*
K o e n ig sb e rg e r^ i n 1898 found h e m atite to be ferro m ag n e tic
b ut su sp e c te d t h a t th e magnetism was due to adm ixtures of m ag n etite
a lth o u g h chem ical a n aly se s showed l i t t l e o r no FeO.
Westinann*s
p u b lic a tio n s
12
11
data* e rro n e o u sly c it e d even in a u th o r ita tiv e
a s evidence f o r th e ferrom agnetism o f hem atite* a re
c l e a r l y in s ta n c e s o f ferrom agnetism due to th e p resen ce o f m agnetite*
as shown by h is own chem ical a n a ly s is :
Fe203 * 93*63 p e rc e n t; Ti02*
Alpha h e m a tite i s th e common form of Fe203 c r y s t a l l i z i n g i n
th e rhombohedral system and w i l l h e r e a f t e r be r e f e r r e d to a s hema­
t i t e . Gamma h e m atite has th e same cu b ic c r y s ta l s tr u c tu r e as magne­
t i t e , Fe304* b u t has th e chem ical com position Fe203 . I t i s d is ­
t i n c t l y fe rro m ag n e tic b u t somewhat u n s ta b le .
9
^
11
12
Jakob Kunz.
Tt
Neues Jahrbuch f u r M ineralogie* 1 , 1907, p . 62.
J . K oenigsberger, Wied. Ann.* 66, 1898* p . 727.
s/festmann.
D is s e r ta tio n , Upsala* 1896.
I n te r n a tio n a l C r i t i c a l T a b le s.
1929* p* 4J-4*
McGraw-Hill Book Company* 6*
5
3.55 p e rc e n t; FeO, 3.26 p e rc e n t.
This amount of FeO corresp o n d s to
1 0 .8 p e rc e n t Fe304 , and t h i s amount i s s u f f i c i e n t to obscure any f e r ­
rom agnetic in flu e n c e o f h e m a tite .
Ytfhen i t i s c o n sid e re d t h a t magne­
t i t e i s 10,000 tim es as m agnetic a s h e m a tite , ?festmann!s d a ta must be
excluded as in d ic a tio n s o f th e ferrom agnetism of h e m a tite .
S im ila r
doubts m ight be a tta c h e d t o th e d a ta o f S m ith ^ who made v e ry p re c is e
measurements on c r y s t a l s o f h e m a tite .
Smith g iv es no chem ical a n a ly s is
and e v id e n tly assumed th e c i y s t a l l i n e form to be an in d ic a tio n o f h ig h
p u r it y .
I t i s w e ll know n^ t h a t FeO and Fe203 form s o li d s o lu tio n s
which can form p e r f e c t c r y s t a l s .
D esp ite th e p re c is io n o f S m ith s
m easurem ents, h is d a ta were n o t s u ita b le f o r th e purpose i n view because
o f th e wide v a r ia tio n in v a lu es w hich should be c h a r a c t e r i s t i c c o n sta n ts
o f th e m a te r ia l.
The w ide divergence in th e s u s c e p t i b i l i t y
(20 x 10
15
o f h e m atite
—
6 to 5000 x 10 6 ) found by numerous in v e s tig a to r s has been
e x p la in e d in many w ays.
1 ZL
C h ev alier and Begui*1-0 a s c rib e th e h ig h su s­
c e p t i b i l i t y v a lu es to th e p resen ce o f a lk a lin e im p u ritie s a s do Herroun
13
T. T. Sm ith.
8, 1916, p . 721.
The M agnetic P r o p e r tie s o f H em atite.
Phys. Rev.
J . W. G reig, H. E. Merwin, E. POsnjak, and R. B. Sosman.
E q u ilib riu m R e la tio n s h ip s o f Fe304, Fe203, and 0 . Amer. J o u r. S c i .,
30, 1935, PP. 239-316.
^ Throughout t h i s p ap er s u s c e p t i b i l i t y s h a l l mean th e mass su s­
c e p t i b i l i t y Xg, u n le ss o th erw ise s t a t e d .
16
R. C h ev alier and Z. E. B egui. Thermomagnetic P r o p e r tie s of
F e r r ic O xide. S o c ie te 1 Chimique, Nov. 1937, pp. 1735-41.
6
and W ilson
17
and Duparc.
18
O thers have e x p lain ed t h i s as due to th e
19
mode o f p re p a ra tio n
and to n a t u r a l l y o c c u rrin g fe rro m ag n e tic f e r r i c
20
21
oxide*
S to n er
concludes t h a t p u re Fe203 i s p ro b ab ly n o t ferrom ag­
n e t i c and b e lie v e s t h a t a no n ferrom agnetic sesq u io x id e can be p re p a re d .
T his i s somewhat of th e f e e lin g p o sse sse d by some o f th e French sch o o l
o f m in e ra l p h y s ic is ts even th o u g h n a tu r a l h e m a tite s were shown to e x h i b i t such in d ic a tio n s o f ferrom agnetism a s a d e f i n i t e C urie p o in t
22
independent o f th e method o f p re p a ra tio n o f th e Fe203 , and v a r ia tio n o f
23
s u s c e p t i b i l i t y w ith g ra in s i z e .
The f i r s t in d ic a tio n s t h a t h e m atite r e a l l y p o sse sse s a h ig h
c o e rc iv e fo r c e and m ight be cap ab le of c o n c e n tra tio n on an a l t e r n a t i n g c u rre n t s e p a ra to r w ere n o tic e d by D avis and a t about th e same tim e by
Sokolovsky,
17
E. W ilson and E. F. H erroun.
P ro c. Phys. S o c ., 33, 1921, p .
196.
18
^
L. Duparc and co-w o rk ers.
B u ll. Soc. M in., 37, 1914, p . 28.
G. F. H u ttig and H. K u tte l.
Z e it . Anorg. Chem., 199, 1931* P*
129.
20
R. B. Sosman and E. P o sn jak .
(August 1925).
21
Edmund C. S to n e r.
London, 1934, p« 529.
Jo u r. Wash. A cad., 15, no. 14
Magnetism and M a tte r.
Methuen and C o., L td .,
22 see fo o tn o te 16.
23
Raymond C h ev a lie r and M ile, Suzanne Mathew. V a ria tio n o f th e
M agnetic S u s c e p ti b ility o f H em atite Powders as a F u n ctio n of th e S ize
o f th e G ra in s. C. R ., 204, 1937, pp. 854-6.
7
S e v e ra l in v e s tig a to r s
24
have been i n t e r e s t e d i n a p p ly in g
M ordey's d isc o v e ry to a lte r n a t in g c u rre n t m agnetic c o n c e n tra tio n and
th e M e ta llu r g ic a l D iv isio n o f th e U n ited S ta te s Bureau o f Mines has
done c o n sid e ra b le re s e a rc h along th e s e l i n e s ,
25
C. W. Davis n o tic e d
^ (a) ¥* M, Mordey. D em onstration o f Some Recent S tu d ie s i n
A lte rn a tin g Magnetism and Some P o s s ib le A p p lic a tio n s . P ro c , Phys. S o c .,
40, 1928, p . 338.
(b) J . A, L. O rtle p p . A lte rn a tin g C u rren t i n M agnetic Separa­
Jo u r. Chem. and Met, Soc. o f South A fric a , 3 °, 1929, pp. 99-128.
tio n .
(c)
B. ¥ . Holman. Recent R esearch i n Ore D re ssin g , IV - Mag­
n e t i c and H y s te re tic S e p a ra tio n . South A frica n Min. and Eng. J o u r .,
36 , p a r t 2, 1925, pp. 138-141, 171-173.
(d)
H. S ta f f o r d H a tf ie ld . The A ction o f A lte rn a tin g and Mov­
in g M agnetic F ie ld s Upon P a r t i c l e s o f M agnetic S u b stan ces. P h y sic s, 7,
no. 2, 1936, p p . 604-10.
25
(a) R. S . Dean, V. H. G o ttsc h a lk , and C. W. D av is. M agnetic
S e p a ra tio n of M in e ra ls. R eport o f I n v e s tig a tio n s 3223, Bureau o f M ines,
1934, PP. 3 -13.
(b) C. ¥ . D av is. A lte rn a tin g C u rren t M agnetic S e p a ra tio n o f
Iro n O res. R eport of In v e s tig a tio n s 3229, Bureau o f M ines, 1934, pp.
35-37.
(c) R. S. Dean and C. ¥ . Davis* M agnetic C o n cen tratio n o f O res,
T ran s. Amer. I n s t . Min. and Met. E n g ., 112, 1934, PP* 509-537.
(d) V. H. G o ttsch a lk and C. TfiT. D av is. A pparatus f o r D eterm ining
M agnetic C onstants o f M ineral Powders. R eport of I n v e s tig a tio n 3268,
Bureau o f M ines, 1935, pp. 51-67.
(e) C. ¥ . D avis. M agnetic P r o p e r tie s o f M in eral Powders and
T h e ir S ig n ific a n c e . I b id , pp. 91-101.
(f ) C. ¥ . D avis. P r a c t i c a l A spects o f A lte rn a tin g C urrent Mag­
n e tic S e p a ra tio n . I b id , p p. 91, 107*
(g) Donald Jay Doan. E f fe c t o f L a ttic e D is c o n tin u itie s on th e
M agnetic P r o p e r tie s o f M ag n etite. R eport o f I n v e s tig a tio n 3400, Bureau
o f M ines, 1938, p p. 65 - 86 .
8
t h a t i f h e m atite p a r t i c l e s w ere m agnetized i n a stro n g d i r e c t c u rre n t
m agnetic f i e l d and p la c e d on an a lte r n a t in g c u rre n t s e p a r a to r , th e y
showed a f a i n t h y s te r e ti c o r r e p e llin g a c tio n .
No q u a n tita tiv e r e s u l t s
were o b ta in e d a t th e t i n e because th e fo rc e of re p u ls io n appeared to be
so sm all t h a t i t co u ld n o t be u sed f o r a s e p a ra tio n p ro c e s s .
N everthe­
l e s s , th e r e s u l t s showed t h a t h e m atite had a remanence and a co erciv e
fo rc e .
In 1935, S o k o lo v sk y ^ found th e same a c tio n and made q u a n tita ­
t i v e t e s t s on th e amount o f re p u ls io n i n v a rio u s f i e l d s and a t d i f f e r e n t
fre q u e n c ie s of a l t e r n a t i o n .
In th e co u rse o f h is experim ents he reached
th e same c o n clu sio n s concerning a lte r n a t in g c u rre n t m agnetic s e p a ra tio n
a s D avis, Dean, and G o ttsch a lk o f th e Bureau of Mines) namely, t h a t a
m a te ria l-m u st have a high c o e rc iv e fo rc e as w e ll as a h ig h p e rm e a b ility
i f a lte r n a t in g c u rre n t m agnetic s e p a ra tio n i s to be f e a s i b l e .
Sokolovsky
perform ed a lte r n a t in g c u rre n t s e p a ra tio n s on h e m atite o f h ig h p u r it y
(69.60 to 70.05 p e rc e n t) and found t h a t i f h e m atite was f i r s t na c tiv a te d ”
by m a g n e tiz a tio n i n a f i e l d o f 4,000 to 5,000 o e rs te d s , and th e n p la ce d
over an a lte r n a t in g c iirre n t magnet, a d e f i n i t e re p u ls io n to o k p la c e , de­
pending on th e freq u en cy of a l te r n a t io n and th e s iz e o f th e h e m atite
g r a in s .
This shows d e f i n i t e l y t h a t h e m atite i s ferro m ag n etic b u t Soko27
lo v sk y was more concerned w ith a v e r i f i c a t i o n o f O r tle p p 's
work on
m agnetic s e p a ra tio n and seem ingly reco g n ized n o th in g new in t h i s p ro p e rty
o f h e m a tite .
G.
S. Sokolovsky. Use o f A lte rn a tin g M agnetic F ie ld s f o r E le c tro ­
m agnetic Enrichment o f O res. Mechanobr, 1 5 th Year J u b ile e Volume, 1935,
pp. 523-542.
^
See fo o tn o te 24 b .
9
Smith*s work i s th e only one found in th e l i t e r a t u r e t h a t
q u o tes any f ig u r e s f o r th e c o e rc iv e fo r c e and remanence o f h e m a tite ,
b u t due to th e few v a lu es g iv en th e r e i s l i t t l e p o s s i b i l i t y o f ap p ly ­
in g h is d a ta to commercial m agnetic s e p a ra tio n .
10
GENERAL CONSIDERATIONS
H y steresis*
H y ste re s is in magnetism has been s tu d ie d so ex ten ­
s iv e ly during th e p a s t c e n tu ry t h a t th e r e i s l i t t l e need to d is c u s s
more th a n th e elem entary f a c t s of a h y s te r e s is lo o p .
F ig u re 1 re p re ­
s e n ts a c h a r a c t e r i s t i c curve f o r h y s te r e s is i n a ty p i c a l fe rro m ag n e tic
m a te r ia l and shows th e main p o in ts o f i n t e r e s t :
th e maximum mag­
n e tic f i e l d u se d , Bp, th e m agnetic remanence o f th e m a te ria l a f t e r mag­
n e t i z a t i o n , and Hc , th e c o e rc iv e f o r c e , which i s th e n e g a tiv e f i e l d
re q u ire d to reduce th e r e s id u a l magnetism to z e ro .
Although th e p o in t
HpC i s o f l i t t l e i n t e r e s t in o rd in a ry fe rro m a g n e tic s, i t ta k e s on somewhat more im portance i n t h i s problem .
Spooner
c a l l s t h i s th e open-
c i r c u i t c o e rc iv e fo r c e , by which i s meant th e re v e rs e m agnetizing fo rc e
n e c e ssa ry to leav e th e sample i n a s t a t e o f zero m a g n etiza tio n a f t e r
th e m agnetizing fo rc e has been removed.
This v a lu e i s not a c o n sta n t
o f th e m a te ria l b u t i s r a th e r a fu n c tio n o f th e dim ension r a t i o i f th e
m agnetic t e s t i s n o t made i n a c lo se d c i r c u i t .
The t r u e Hc v alu e i s
t h a t o b ta in e d under c lo s e d - o r o p e n -c irc u it c o n d itio n s when th e de­
m agnetizing fo rc e red u ces th e remanence to zero w h ile th e dem agnetizing
fo r c e i s s t i l l a p p lie d .
I f th e Hc value o f m agnetizing fo rc e i s r e ­
moved, th e in d u c tio n r i s e s to f .
The o p e n -c irc u it c o erciv e fo rc e i s
th e v a lu e o f th e dem agnetizing f i e l d which when removed w i l l cause th e
in d u c tio n t o r i s e to zero along g - o .
A lthough th e H i s o f d o u b tfu l
oc
v a lu e , i t w i l l be used l a t e r i n d is c u ssin g th e dem ag n etizatio n of h e m a tite .
28
T. Spooner. P r o p e r tie s and T estin g of M agnetic M a te ria ls .
McGraw-Hill Book C o., 1927, pp. 62-65.
Virgin curve
H max.
-H
+H
oc
M -3
S2
Figure
1
. — Hysteresis
l oop o f a f e r r o m a g n e t i c s u b s t a n c e .
Property ef the
ca
BUREAU OF MINES
A P A R T M E N T OF THE I NTE
N e t te b e nsftd for any p u rp ose
n tftiw ut auiteW e ?.c Kp.c '.v !c ^
n
N om enclature.
Q uantity _________
Symbol
: ______ U nit
M agnetic in d u c tio n
B
Gauss
Remanence
Br
Gauss
M agnetic f i e l d
H
O ersted
Maximum m agnetic f i e l d
^max
O ersted
C oercive fo r c e
Hc
O ersted
M ag n etizatio n d e n sity *
4^1
Gauss
Volume s u s c e p t i b i l i t y
k
Mass s u s c e p t i b i l i t y
F ie ld g ra d ie n t
g
ah
*T. F . Wall* A pplied Magnetism, London, E. Benn, L td .,
1927, p . 72.
12
MATERIAL USED
P u r ity o f h e m a tite s .
be over-em phasized*
The im portance o f p u r it y o f h e m atite cannot
Herroun and ¥ i l s o n ^ have a p tly summed up th e s i t ­
u a tio n a s fo llo w s :
When i t i s remembered t h a t one p a r t o f carbon can r e ­
duce e ig h ty tim e s i t s own w eight o f Fe203 to Fe304, and
t h a t th e s u s c e p t i b i l i t y o f m ag n etite i s some te n thousand
tim es g r e a te r th a n t h a t o f Fe203, th e enormous e r r o r t h a t
can be in tro d u c e d by tr a c e s o f organic im p u rity w i l l be r e ­
a liz e d ; i n f a c t , th e r e i s l i t t l e doubt t h a t th e change in
s u s c e p t i b i l i t y brought about by h e a tin g pure Fe203 w ith any
su b sta n c e capable o f red u cin g i t would be a more d e lic a te
t e s t f o r , sa y , o rg an ic carbon o r hydrogen th a n any o th e r
a t p re s e n t known.
A fte r c o n sid e rin g th e wide v a r ia tio n in s u s c e p t i b i l i t y o f
Fe203 produced by many d if f e r e n t chem ical p ro c e s s e s , one a r r iv e s a t
th e c o n clu sio n t h a t i t i s extrem ely d i f f i c u l t to g et pure Fe203 .
A n aly sis o f h e m a tite f o r gamma Fe203 co n ten t and even f o r sm all amounts
of
Fe304 i s p r a c t i c a l l y im p o ssib le.
An amount
o f Fe304
so sm all t h a t
it
cannot be d e te c te d ch em ically i s s u f f i c i e n t
to cause
a la rg e in ­
c re a s e i n th e s u s c e p t i b i l i t y o f h e m a tite .
N e ith e r sp e c tro g rap h ic
a n a ly s is nor X -ray work can d e te c t th e presen ce o f vexy sm all amounts,
sa y , le s s th a n 0 .1 p e rc e n t, o f alp h a o r gamma Fe203 in Fe304, o r v ic e
v e rsa .
The q u e stio n th e n a r i s e s —how do we know t h a t th e ferro m ag n etic
p r o p e r tie s m easured in t h i s work were a c tu a lly th o se of h em atite?
The
answ er to t h i s w i l l be found i n th e d is c u s s io n which shows t h a t th e
method developed f o r th e s e measurements i s probably th e most s e n s itiv e
means known f o r d e te rm in a tio n of m agnetic im p u ritie s i n h e m a tite .
29
See fo o tn o te 17.
13
Source and a n aly se s o f h e m a tite s .
Three n a tu r a l h e m a tite s and
one l o t of a r t i f i c a l Fe 203 were used in t h i s ex p erim en tal work*
The
f i r s t h e m a tite was one from Cumberland, England, purchased th ro u g h
Ward*s N a tu ra l S cience E sta b lish m en t, Inc*
I t was broken down to
-6 mesh, u sin g a b ra s s hammer and aluminum p l a t e , ground i n a pebble
m i l l f o r about 6 h o u rs, and th e n f r a c tio n a te d in to v a rio u s s iz e s by
means o f a R o lle r-^ a i r analy zer*
A ll s iz e f r a c tio n s were checked
m ic ro s c o p ic a lly and found t o have l e s s th a n about 3 p e rc e n t ov ersize*
The chem ical a n a ly s is f o r each o f th e a ir-a n a ly z e d f r a c tio n s i s as
fo llo w s :
•
•
S iz e i n m icrons
0
5
10
20
40
to
to
to
to
to
5
10
20
40
74
*
•
: Fe p e rc e n t : I n s o l, p ercen t
6 6 .0 2
65 .1
65*6
65.9
67.2
3 .5
4 .6
4 .7
4.5
2.5
These a n a ly se s account f o r about 93-1/2 p e rc e n t of th e ma­
t e r i a l s p re s e n t i f th e assum ption i s made t h a t a l l ir o n i s p re s e n t as
Fe203 .
An extrem ely low p ercen tag e o f th e g ra in s in any one f r a c tio n
were a t t r a c t e d by a m agnetized n eed le observed under th e m icroscope.
H em atite no. 1 was from th e Michigan iro n ra n g e .
No chem ical
a n a ly s is was made on t h i s sample b u t magnetic measurements showed i t to
be alm ost f r e e of m agnetic im p u r itie s .
This h em atite came in m assive
3° p t s . R o lle r. S e p a ra tio n and S ize D is trib u tio n of M icroscopic
P a r t i c l e s —An A ir A nalyzer f o r Fine Powders. R eport o f I n v e s tig a tio n s
3268, Bureau o f M ines, 1935*
14
lumps rem arkably homogeneous and la rg e enough to y i e l d ro d s 3 /8 in c h
sq u are and 4 in c h es lo n g .
The measurement on th e s e ro d s p ro v id e w el­
come c o rro b o ra tio n of th e assum ption th a t th e mass s u s c e p t i b i l i t y i s
c o n sta n t r e g a rd le s s o f th e d e n s ity .
One a i r f r a c t i o n and two s ie v e
f r a c t i o n s a ls o were made from th e rem ainder of th e o re .
No. 2 h e m a tite had th e fo llo w in g a n a ly s is :
P ercen t
Iro n
Phosphorus
S ilic a
66.94
,054
2.10
Manganese
.16
Alumina
.54
M agnetic measurements in d ic a te d th e p resen ce of some mag­
n e tic im p u rity in, amounts s u f f i c i e n t to cause abnorm al s u s c e p t i b i l i t i e s .
The a r t i f i c i a l Fe 203 ‘was B aker!s A nalyzed F e r r ic Oxide,
Powdered, Lot no. 4137.
P re lim in a ry measurements were made on th e Nagaunee, M ichigan,
31
h e m a tite , which s in c e th e in v e s tig a tio n s o f Cooke"^ has been used f r e ­
q u e n tly as a •typical American ir o n o re .
This m a te ria l was n o t c o n sid ered
i n th e f i n a l d e f i n i t i v e measurements because i t c o n tain ed too much mag­
n e t i t e or gamma h e m a tite .
31
S. R. B. Cooke. M icroscopic S tru c tu re and C o n c e n tr a tib ility
o f American Iro n O res. B u lle tin 331> Bureau o f M ines, 193&.
15
THEORY
Fundamental e q u a tio n s .
The methods g e n e ra lly u sed f o r m easuring
fe rro m a g n e tic su b sta n c es a re n o t s u ite d f o r u se on h e m a tite because
th e e f f e c t s a re so sm all t h a t th e y would be masked by in s tru m e n ta l
e r r o r s ; th e r e f o r e , a n o th e r method was u sed which depends on th e fo rc e
K e x e rte d by a nonhomogeneous f i e l d on a t e s t body.
This i s not new
and a lth o u g h i t h a s been d is c u s s e d in many te x tb o o k s a review o f th e
two p r i n c i p a l methods w i l l be g iv en h e re because b o th were u sed in t h i s
w ork.
Much o f what fo llo w s i s p a tte rn e d a f t e r th e e x c e lle n t p re s e n ta -
t i o n given by Klemm.
32
The fo rc e K which a c ts on a body o f m agnetic moment M in a
nonhomogeneous f i e l d
^ H i s given by th e e q u a tio n ^
y*
1 . K = H.AH
A body o f s u s c e p t i b i l i t y k ta k e s on th e moment kH p er cnr
i n a f i e l d H and, f o r a sm a ll volume, eq u atio n 1 becomes
2.
dK = kKLM dv
£x
S t r i c t l y sp eak in g , t h i s e q u atio n i s d e riv e d f o r a body of
c o n sta n t s u s c e p t i b i l i t y whose m agnetic moment i s g e n e ra te d by th e ex­
t e r n a l f i e l d and f o r t h a t re a so n some of th e r e s u l t s p re s e n te d h e re in
a re open to th e c r itic is m t h a t th e s u s c e p t i b i l i t y v a lu es a re n o t id e a l
s u s c e p tib ilitie s .
32
B i t t e r 34 e x p lain s t h i s d iffe re n c e between r e v e r s ib le
W ilhelm Klemm.
M.B.H*, L e ip z ig , 1936.
Magnetochemie, Akademische V e rla g s g e s e lls c h a ft
33 This e q u atio n i s d e riv e d by ta k in g moments o f a body in a
m agnetic f i e l d .
34 F ra n c is B i t t e r . In tro d u c tio n to Ferrom agnetism .
Book C o., Hew York, 1937, p . 181.
McGraw-Hill
16
s u s c e p t i b i l i t y and t r u e p a ra - o r diam agnetic s u s c e p t i b i l i t y a s a hys­
t e r e s i s phenomenon.
The e r r o r s in tro d u c e d in t h i s work by th e use
o f e q u a tio n 2 a r e sm all due to th e f a c t t h a t th e r e v e r s ib le s u s c e p ti­
b i l i t y d i f f e r s very l i t t l e from th e id e a l f o r even la r g e in c re a s e s in
H because th e s u s c e p t i b i l i t y v a lu es f o r h e m atite a re o f th e same mag­
n itu d e a s a s tro n g ly param agnetic s u b sta n c e .
In a tr u e ferro m ag n e tic
th e v a lu e of k i s a complex fu n c tio n o f H a t low f i e l d s , b u t in th e
neighborhood of s a tu r a tio n k i s c o n s ta n t.
In a b ro ad er sen se , th e
whole b a s is f o r th e e x p e rim e n ta l method used i s th e f a c t t h a t h em atite
has an i r r e v e r s i b l e s u s c e p t i b i l i t y .
Methods of s u s c e p t i b i l i t y measurements based on e q u atio n 2
may be d iv id e d in to two d i s t i n c t c la s s e s :
(1) The t e s t body i s so
sm all t h a t H-&S may be c o n sid e re d c o n sta n t and th e d i f f e r e n t i a l equat i o n 2 can be used d i r e c t l y , and (2) th e t e s t body becomes so la rg e
t h a t (2) must be in te g r a te d :
K = k
H-iL£
ax
dv
Measurements based on th e d i f f e r e n t i a l e q u atio n .
H.
and H-M
The q u a n titie s
f o r a normal electrom agnet w i l l be c o n sid ered f i r s t .
In f ig u r e 2A th e l i n e s of fo rc e proceed along 6 from th e n o rth p o le
to th e south p o le .
C onsider a sm all param agnetic body p la ce d in th e
f i e l d a t p o in ts in d ic a te d by th e
c irc le s .
The Induced moments a re
in d ic a te d by th e sm all arrow s w ith in th e c i r c le s w h ile th e fo rc e s a c t ­
in g on th e body due to th e p roduct
th e l a r g e r arrovrs.
along th e x a x is a re shown by
The fo rc e s h e re co n sid ered a c t along th e p o s itiv e
v a lu e s o f x , t h a t i s , p e rp e n d ic u la r to th e d ir e c tio n o f th e induced
moments.
+y
-X
+x
-X
+y
-y
- 9 H y Ibx
Hy* 3 Hy 19 X
-y
orces
in
the
nonhomogeneous
field
of
an
+X
electromagnet.
Forces
A
involved
in
N
N
formal
magnetization
t h e Gouy m e t h o d .
B
of
a
ferromagnetic
in
Test
Gouy m e t h o d .
body m a g n e t i z e d
D
Figure
2
normally;
-H<HC
S+
° r c p e r ty o'
The
bureau of aumfs
D E P A H T IviE N 7 OF THE INTERIOR
Piet I f bfc >S80 !or 3ny purpose
W'tPouT s u i t a b l e a c k n o w i e c k
r-^nt
17
The d ir e c tio n o f th e fo rc e e x e rte d by th e f i e l d on p a ra ­
m agnetic and fe rro m ag n e tic b o d ie s i s always tow ard th e m idpoint of
th e f i e l d , f o r i t i s determ ined by th e sig n o f
-is.
This d i f f e r e n t i a l
ax
c o e f f ic ie n t i s p o s itiv e on th e l e f t s id e and hence th e fo rc e p ro p o r­
t i o n a l to
a c ts i n th e d ir e c tio n o f in c re a s in g v a lu es o f x , th a t
i s , in to th e f i e l d .
Even though H-—~ i s n e g a tiv e on th e r ig h t s id e
( f ig u r e 2A), th e r e i s a re p u ls io n i n th e d ir e c tio n o f p o s itiv e v a lu es
o f x and th e r e i s s t i l l a t t r a c t i o n tow ard th e c e n te r of th e f i e l d .
Measurements b a se d on th e d i f f e r e n t i a l eq u atio n a re g e n e ra lly
re la tiv e .
In o th e r w ords, th e fo rc e e x e rte d on a t e s t body in a d e f i n ite
p o r tio n of th e f i e l d i s compared w ith the- fo rc e e x e rte d on a bocfcr of
known s u s c e p t i b i l i t y p la c e d in e x a c tly th e same p o s itio n .
35
g e n e ra l method used by a number of e x p erim en ters.
This was th e
Extreme c a re must be used i n t h i s method always to b rin g th e
t e s t body to th e same p o s itio n i n th e f i e l d t h a t th e known bocfcr oc­
cu p ied .
This d i f f i c u l t y has l a r g e ly been overcome by making th e form
o f th e p o le fa c e s such t h a t H-Al i s a c o n s ta n t.
This arrangem ent has
been d e sc rib e d by F ereday-^ and more re c e n tly by Rogers and Stamm.3?
35 (a) M. F araday. Experim ental R esearches.
London, 3, 1855, PP* 27, 497.
Taylor and F ra n c is ,
(b) P. C u rie . M agnetic P r o p e r tie s of Substances a t V arious
T em peratures. Ann. de Chim. e t P h y s., 5, 1895, p . 289.
(c) C. Cheneveau.
(d) G. Foex.
1921, p . 174.
3^ R. A. F ereday.
P h il . Mag., 20, 1910, p . 357.
R esearches on Paramagnetism.
Ann. de P h y s., 16,
P ro c. Phys. Soc. (London), 44, 1932, p . 274.
37 B. A. Rogers and K. 0 . Stamm.
An A pparatus f o r D eterm ining Thermo-
m a g n etic B ehavior o f S la g s, and Some P re lim in a ry R esu lts O btained w ith I t .
A.X.M.M.E., M etals Technology, T. P. 1133, December 1939.
IS
The a p p a ra tu s developed by Rogers and Stamm, was used f o r th e p o rtio n
o f t h i s work on th e therm om agnetic p ro p e rtie s o f h e m atite and found
to be s a tis f a c to r y *
Methods of measurement depending on th e in te g r a te d e q u a tio n .
Methods u sin g a c y lin d r ic a l t e s t body38 extending a c o n sid e ra b le d is ­
ta n c e along th e X a x is (f ig u re 2B) a re o f g r e a te r im portance th a n
th o s e u sin g a sm all sp o t of th e nonhomogeneous f i e l d .
I f A dx i s
s u b s tit u te d f o r dv where A i s th e c r o s s - s e c tio n a l a re a of th e sample,
th e f o r c e a c tin g i n vacuum i n th e d ir e c tio n o f th e X a x is becomes
3.
K=Ak
H
I
J lS
dx = A k
2
4.
where
K = 1 /2 A k
2nd
1
H . d H
A
2
“
H
2
)
a re th e v a lu es o f H a t
and x .
In t h i s work th e
p o s itio n and le n g th of th e t e s t sample were chosen such th a t
2
n e g lig ib le in com parison w ith
, and 4 becomes
5.
2
was
K = 1 /2 A H2,max.
and th u s we have an in te g r a tio n of th e fo rc e s a c tin g a l l along th e tube,
Transposing 5
6
•
k =^
AH2
Xg = m s s s u s c e p t i b i l i t y = d^ J i t y
2
^
=
= 2 K x v o l. f i l l i n g _______________
o r ig i n a l w eight o f m a te ria l x A x H
^ This i s g e n e ra lly c a lle d th e method o f L. G. Gouy.
C. R. Acad.
S c i ., P a r is , 109, 1889, p . 935, but was f i r s t given in p r in c ip le by J .
P lu c k e r, Pogg. A nn., 91, 1854, p . 1 .
19
Xg = 2 x g a in i n w eig h t x 980 x vol* f i l l i n g
A =
x o r i g i n a l w eight of sample
volume o f f i l l i n g
A
« h e ig h t o f f i l l i n g
a ls o 1000 mg. * 1 gram
9.
X - 2 x g a in i n w eight i n mg* x h e ig h t o f f i l l i n g
g
■'
■ ■ —
• ■' ■—
—
‘
-----------------------
•------------ -- ---------------------
H x o r ig . w t. x 1*019
E quation 9 i s th e form u sed f o r computing most o f th e ex­
p e rim e n ta l d a ta given below.
20
EXPERIMENTAL
A p p aratu s.
The Gouy-type m agnetic b a lan c e used f o r s u s c e p t i b i l i t y
d e te rm in a tio n s i s shown in f ig u r e 3*
It- c o n s is ts e s s e n t ia l ly of a chem­
i c a l b a lan c e p la c e d on a s ta n d covering an e lectro m ag n et, a sample h o ld e r,
and a d ev ice f o r p re v e n tin g f r i c t i o n between th e sample tu b e and th e mag­
n e t p o le f a c e s .
The chem ical b a lan c e was o f th e type commonly used in quant­
i t a t i v e chem ical a n a ly s is .
The le f t- h a n d pan was removed, two h o les
d r i l l e d i n th e b alan ce case d i r e c t l y b en eath th e hanger arm and a p ie c e
of m a g n e tic a lly i n e r t b ra s s w elding rod passed through th e case to serve
as a suspension f o r th e sample h o ld e r.
A ll balance p a r ts were nonmag­
n e tic .
The sample h o ld e r was a b ra s s tu b e 5 in ch es in le n g th and
0.25 in c h i n t e r n a l d ia m e ter.
The tu b e was m a g n e tic a lly i n e r t w ith in
th e p r e c is io n o f measurement over th e range o f f i e l d s tre n g th s from 500
to 10,000 o e rs te d s .
I t was suspended from th e b ra s s rod by means o f a
copper w ire .
The Gouy b a lan c e i s so w e ll known t h a t no f u r th e r d e s c rip tio n
i s n e c e s sa ry .
I t i s n o t s u ite d f o r measurements in v o lv in g s tro n g ly f e r ­
rom agnetic m a te ria ls because o f th e a t t r a c t i o n of th e sample to th e
p o le f a c e s .
This adherence of th e sample to th e p o le fa c e was ev id en t
f o r a weak fe rro m ag n e tic l i k e h e m atite in f i e l d s above 2,000 o e rs te d s .
Of th e v a rio u s methods t r i e d f o r p re v e n tin g e r r o r due to t h i s e f f e c t ,
th e most s a t i s f a c t o r y was th e v ib r a tio n of two t i g h t l y s tre tc h e d w ire s
p a r a l l e l to th e po le f a c e s .
39
V/hen a sm all a lte r n a t in g c u rre n t p a sse s
^ S. S. S c h a ffe r and N. W. T a y lo r. E ffe c t of Complex Io n Forma­
t i o n Upon th e M agnetic S u s c e p tib ility of Param agnetic S a lts in Aqueous
S o lu tio n . Jo u r. Araer. Chem. S o c ., 4&> 1926, p . 843*
F ig u re 3* - Gouy-type m agnetic b a la n c e
21
th ro u g h such -mires s tr e tc h e d in a m agnetic f ie ld * th e y v ib r a te m ith
th e freq u en cy o f th e a lte r n a t i n g c u rre n t i f th e c o rre c t te n s io n i s
a p p lie d to th e m ire s .
The p ro p e r te n s io n may be computed from th e
fo llo w in g c o n s id e ra tio n s :
The ex act fundam ental freq u en cy o f a
s tr e tc h e d s tr in g i s giv en by
n
L
T
m
=
=
=
freq u en cy
le n g th
te n s io n
mass p e r -unit le n g th
This p e rm its th e c a lc u la tio n o f th e ex act te n s io n n e c e ssa ry when th e
fundam ental freq u en cy i s known.
In t h i s case 60 cy cle a lte r n a tin g cur­
r e n t mas used and th e te n s io n on th e m ire a d ju s te d f o r maximum a t t r a c ­
t i o n of th e c u rre n t-c a r ry in g co n d u cto r.
The am plitude o f th e v ib r a tio n
mas so sm all t h a t i t d id no t i n t e r f e r e w ith th e b alan ce weighings* and
th e f r i c t i o n o f th e tu b e on th e p o le fa c e mas reduced to a minimum dur­
in g th e course o f th e m easurem ents.
This device made i t p o s s ib le to
extend th e use o f th e Gouy b alan ce to f i e l d s f a r beyond th o se p o s s ib le
o th e rw ise .
The magnet mas an electrom agnet of th e Cenco ty p e .
I t had
alm ost th e maximum number of ampere tu rn s p e rm issib le w ith o u t r e s o r t
to w ater c o o lin g .
The p o le p ie c e s were low -carbon co n ten t s o f t ir o n ,
th re a d e d on one end so t h a t th e a i r gap could be a d ju s te d to any d e s ire d
w id th .
I t was found most convenient to use th e f l a t p o le fa c e s r a th e r
th a n th e c o n ic a l ones a v a ila b le .
The p o le fa c e s used were 8 c e n tim e te rs
i n d iam eter and t h e a i r gap was approxim ately 1.25 c e n tim e te rs .
At 11
amperes a f i e l d s tr e n g th of alm ost 1 0,0 0 0 o e rs te d s was a tta in e d in th e
a i r gap.
A c a li b r a t io n curve f o r th e s e c o n d itio n s i s shown in fig u r e 4«
22
S lid e w ire r e s is ta n c e s c o n tr o lle d th e c u rre n t s u p p lie d and a double­
s c a le ammeter was used to m easure th e c u r r e n t,
A re v e rsin g sw itch was
p ro v id e d f o r re v e rs in g th e d ir e c tio n of m ag n etiza tio n a c ro ss th e a i r
gap.
The C u rie -ty p e b a lan c e u sed f o r a sm all p o rtio n o f t h i s work
to o b ta in therm om agnetic d a ta was t h a t designed and b u i l t by Rogers and
StanmA0 f o r measurements on s la g s a t th e P itts b u r g h S ta tio n o f th e U.
S , Bureau o f M ines,
The main f e a tu r e o f t h e i r m o d ific a tio n of C u rie ’s
a p p a ra tu s i s th e use of a s p e c ia l-ty p e p o le fa c e p ro p e rly shaped to
make th e p ro d u c t B i l l a c o n s ta n t. The tem p eratu re in a sm all fu rn ace
dx
i n s e r te d between th e p o le fa c e s co u ld be c o n tro lle d v ery a c c u ra te ly .
A G rassot flu x m e te r, s u p p lie d by th e C e n tra l S c ie n tif ic C o.,
was used as a check f o r f i e l d s tre n g th d e te rm in a tio n s.
The c u rre n t gen­
e r a te d by w ithdraw ing a se a rc h c o i l o f known a re a tu rn s from th e c e n te r
o f th e m agnetic f i e l d was measured in term s o f maxwells by th e fluxm eter*
The se a rc h c o ils were c a lib r a te d by comparison w ith s ta n d a rd c o ils o f
known a re a tu r n s a t th e N a tio n a l Bureau o f S tan d ard s, W ashington, D. C.
C a lib r a tio n . The f i e l d s tre n g th appears in form ula 9 as th e square
and hence must be determ ined w ith accuracy g r e a te r th a n s u f f ic e s f o r
th e o th e r v a r ia b le s .
a s ta n d a rd .
The method f i n a l l y u sed was t h a t o f comparison w ith
The g a in i n w eight o f a param agnetic substance o f known sus­
c e p t i b i l i t y in v a rio u s f i e l d s was found and th e n s u b s t it u te d i n th e
e q u a tio n
X = 2 x le n g th x g a in in w eight
® o r ig i n a l w eight x
x l7 6 l9
See fo o tn o te 37.
23
V alues o f H were c a lc u la te d and p lo tt e d a g a in s t th e c u rre n t producing
th e f i e l d .
T his method has been e x te n s iv e ly used by th e French school
o f p h y s ic i s ts and o th e rs u sin g th e Curie-Cheneveau ty p e b alan ce f o r i n ­
v e s ti g a tio n o f p a r a - and diam agnetic s u b sta n c e s,
S to n e r^ s ta te s :
Any method o f m easuring s u s c e p t i b i l i t y in v o lv in g
th e use o f a homogeneous f i e l d may be in v e rs e ly employed
f o r th e d e te rm in a tio n o f unknown f i e l d s u sin g su b stan ces o f
known s u s c e p t i b i l i t y .
S a tis f a c to r y sta n d a rd s having a h ig h e r s u s c e p ti­
b i l i t y th a n w a te r a re v e ry d e s ir a b le . Manganese pyrophos­
p h a te , Mn2P 207 , has been u sed f o r t h i s purpose, th e su s­
c e p t i b i l i t y of a specimen c a r e f u lly p re p a re d a t S trasb o u rg
having been found to rem ain in v a r ia b le (Xg * 103,1 x 10~°)
over a p e rio d o f y e a r s ; b u t th e s u s c e p t i b i l i t i e s o f specimens
p re p a red in d if f e r e n t ways may d i f f e r by as much as 2 p e rc e n t.
W ith param agnetic s ta n d a rd s i t i s , of c o u rse, e s s e n t ia l to
ta k e i n t o account th e v a r ia tio n o f s u s c e p t i b i l i t y w ith tem­
p e r a tu r e .
Manganese pyrophosphate was s e le c te d as a s ta n d a rd because o f
i t s high s u s c e p t i b i l i t y , nonhygroscopic p r o p e r tie s , and ease of handling
i n a powder form .
A pparently th e r e i s no s a ti s f a c to r y e x p la n a tio n o f
th e v a r ia tio n o f th e s u s c e p t i b i l i t y w ith th e method of p re p a ra tio n .
It
i s p ro b a b le t h a t c a r e f u l stu d y o f methods of p re p a rin g manganese p y ro i
phosphate would le a d to s p e c if ic a tio n s f o r o b ta in in g a re p ro d u c ib le sta n d a rd .
The Mn2P 2 0? was p re p a red in two ways:
The f i r s t l o t was made
42
according to d ir e c tio n s as given by Treadw ell and H a ll,
To th e s l i g h t l y a c id s o lu tio n c o n ta in in g Mn
e q u iv a le n t to n o t more th a n 0 .$ gram Mn2 P207 iu 250 m l,,
and no o th e r m etals except a l k a l i e s , add 20 g. HC1, 5 t o
10 m l. o f c o ld s a tu r a te d s o lu tio n o f sodium phosphate, and
NH4 0H, drop by drop u n t i l a s lig h t excess i s p re s e n t. Heat
th e s o lu tio n to b o ilin g and keep a t t h i s tem p eratu re f o r
^ E. C. S to n e r,
London, 1934, p . 6 5 .
^
Magnetism and M a tte r.
Methuen and C o., L td .,
E. P. T readw ell and Vf. T. H a ll, A nal. Chem., I I , 1928, p . 133 .
24
th r e e o r fo u r m inutes* o r u n t i l th e p r e c i p i t a t e assumes
a s i l k y c r y s t a l l i n e ap p earan ce. A fte r co o lin g f i l t e r th e
p r e c i p i t a t e in to a Gooch o r Munroe cru c ib le* wash w ith co ld
NH4NO3 so lu tio n * d ry , i g n i t e w ith in a la r g e r c r u c ib le o r i n
an e l e c t r i c fu rn a c e . Cool i n a d e s s ic a to r and weigh as
Mn2P 2 O^.
In d ry in g to c o n sta n t w eig h t a g re a t d ecrease in volume to o k
p la c e b u t no lo s s i n w e ig it a f t e r 1 hour a t about 800° C. i n an e le c ­
t r i c m u ffle .
The o b je c tio n to th e above method i s th e o x id a tio n o f th e
manganous s a l t to th e manganic by a i r i n th e p resen ce o f NH3 as shown
by th e brown d is c o lo r a tio n s found i n th e p ro d u c t.
Another l o t o f
MhgPgOrr was th e r e f o r e p re p a red by a d if f e r e n t p ro ced u re.
Aqueous so­
lu tio n s o f sodium pyrophosphte and manganese s u lf a te were prepared*
m ixed, and H^PsO^ p r e c ip ita t e d .
The MhgPaO^ was f i l t e r e d i n a Gooch
c ru c ib le * washed, dried* and s in te r e d a t 700 to 800° G. f o r 1 h o u r.
M orris Slavin* N onm etallies D iv isio n , Bureau o f Mines, C ollege
Park* Hd.* was k in d enough to run th e q u a lit a t iv e sp e c tro s c o p is a n a ly s is
shown in th e fo llo w in g t a b l e .
TABLE I
Im p u ritie s i n Lot 2, Mn2P2 0rj
P ercen t
Co* Ni* T i, and V
Zr* Sn
Mg, A1
Na
Fe
0 .0 1 to 0 .0 0 1
.001
.0 1 to .1 0
.5 0 to 1 .0
.0 1
25
The a n a ly s is Slows t h a t th e p r e c i p i t a t e was n o t washed f r e e
o f Na2 S0 4 .
S ince th e main e f f e c t o f Na2S04 would be to d i l u t e th e
Mn2P 20 7 * a s u s c e p t i b i l i t y v a lu e o f 102
(xl)
x 10~6 was used in a l l
c a l i b r a t i o n work*
The d iff e r e n c e i n s u s c e p t i b i l i t y of th e Mn2P 20 7 p rep ared by
th e two methods was le s s th a n th e ex p erim en tal e r r o r s o f procedure*
T his i s f u r t h e r su p p o rt f o r th e e x p e c ta tio n t h a t chem ical s tu d ie s m ight
le a d to a method f o r th e p re p a ra tio n o f s ta n d a rd Mn2P2 0 7 o f c o n sta n t and
re p ro d u c ib le s u s c e p tib ility *
There i s an u rg e n t need f o r an i n te r n a tio n a l
s ta n d a rd o f hig h s u s c e p t i b i l i t y and i t i s to be hoped th a t someone w i l l
u n d ertak e such a study in th e n e a r fu tu re *
The a m p e re -fie ld s tre n g th curve o b ta in e d by comparison w ith
th e Mn2P20 7 showed v a r ia tio n s o f l e s s th a n 1 p e rc e n t from th e curve
found by se a rc h c o i l and flu x m ete r measurements*
The s u s c e p t i b i l i t y o f
some common param agnetic su b stan ces was th e n determ ined w ith th e f o l ­
low ing r e s u l t s :
TABLE I I
Comparison o f ex p erim en tal and I n te r n a tio n a l
C r i t i c a l Tables v a lu es f o r some common s a l t s
(Aqueous s o lu tio n )
Substance
HnS04
NiCl 2
N1S04
E xperim ental
v alu e
Xg x 10°
83.2
44.7
26.7
- I* C. T*
v alue
Xg x 106
83.0
45.1
26.9
:
:
;
P ercen t
d iffe re n c e
+ 0 .2
- .9
- .8
26
A ll evidence th u s in d ic a te s th a t f i e l d s tre n g th measurements
w ere a c c u ra te to 1 p e rc e n t.
The v a r i a t io n o f m agnetic im p u ritie s in
h e m a tite and d if f e r e n c e s i n packing th e sample tu b e exceed t h i s accu­
ra c y two to th r e e tim e s .
The a i r gap had a h ig h e r f lu x d e n s ity on going from s tro n g
t o weak f i e l d s and i t was n e c e s sa ry to c a l i b r a t e th e magnet f o r b o th
in c re a s in g and d e crea sin g c u rre n t s tr e n g th s .
This i s undoubtedly due
t o th e fe rro m a g n e tic n a tu re o f th e p o le p ie c e s .
The magnet of th e C urie b alan ce was c a li b r a te d i n th e u su a l
fa s h io n w ith s e a rc h c o i l and b a l l i s t i c galvanom eter.
Rogers and Stamm*s
a p p a ra tu s as o r i g i n a l l y developed gave o n ly r e l a t i v e s u s c e p t i b i l i t y
v a lu e s .
S ince t h e i r l a s t p u b lic a tio n a change i n method of sample
attachm ent has g r e a tly f a c i l i t a t e d measurements and work a lre a d y has
been done on changing r e l a t i v e to a b so lu te v a lu e s .
In t h i s work on
h e m atite th e p u l l on a known mass of Mh2P20 r7 in a known f i e l d was
m easured and unknowns compared w ith i t by means o f th e r e la tio n s h ip :
vA r r = -----------102 x-----------------------10 “^ x —nu— ~xr Ks
"Where X = s u s c e p t i b i l i t y o f unknown
£
102 x 10”^ = s u s c e p t i b i l i t y of Mn2P2 0^
niQ_
= mass o f
m2
= mass o f unknown
} in 2 P 2 0 r ?
« fo rc e to b alan ce known
K2
= fo rc e to balance unknown
U n fo rtu n a te ly , th e balan ce was not s e n s itiv e below 10 m illiam p eres b a l­
an cin g c u r r e n t.
The thermomagnetic d a ta should be ta k e n th e n as in d i­
c a tiv e r a th e r th a n a b s o lu te .
27
P ro ce d u re .
The use of th e Gouy-type m agnetic b alan ce was extended
t o o b ta in s u s c e p t i b i l i t i e s over a la r g e ran g e of f i e l d s tre n g th s and
so p erm it th e p l o t t i n g o f a h y s te r e s is curve from th e d a ta so o b ta in e d .
U su a lly measurements w ith th e Gouy- o r C urie—ty p e b alan ce o p e ra te a t
on ly one f ix e d f i e l d s t r e n g t h .
I t was n o tic e d t h a t when th e sample of h e m atite was tu rn e d
180° p e rp e n d ic u la r to th e d ir e c tio n o f p u ll a f t e r m a g n etiza tio n , th e
m a te r ia l weighed l e s s th a n th e o r ig i n a l sam ple.
show th e d ir e c tio n of m a g n etiza tio n in each c a se .
F ig u res 2C and 2D
F ig u re 2C re p re s e n ts
th e c o n d itio n o f m a g n etiza tio n in th e second quadrant o f a h y s te r e s is
lo o p .
When th e a p p lie d fo rc e becomes la rg e enough to red u ce th e mag­
n e t i z a t i o n in th e sample to z e ro , th e r e i s no lo n g e r a r e p e llin g fo rc e
a s i n f ig u r e 2D, o r an a t t r a c t i n g fo rc e as in fig u r e 2C, b u t a condi­
t i o n o f zero m a g n etiza tio n e x i s t s .
The f i e l d a p p lie d in th e d ir e c tio n
o p p o s ite to t h a t o f m a g n etiza tio n which reduces th e remanence to zero
i s known as th e c o e rc iv e f o r c e .
The procedure f i n a l l y developed f o r determ ining th e h y s te r e s is
loop o f h e m atite by means o f a continuous and u n in te rru p te d s e r ie s of
s u s c e p t i b i l i t y measurements was q u ite d if f e r e n t from th e u s u a l methods
o f f in d in g th e m agnetic p r o p e r tie s of m a te r ia ls .
The fo llo w in g s te p s
show how th e d a ta were o b ta in e d :
1.
The b ra s s sample tu b e was f i l l e d w ith h e m atite powder.
The powder was tamped to give th e same le n g th of sample i n every c a se .
2.
The tu b e was th e n suspended from th e b ra s s w elding rod
and th e w eight of th e sample tube and c o n ten ts balanced e x a c tly by th e
use o f a t a r e .
28
3.
The d i r e c t c u rre n t power f o r th e magnet was th e n a p p lie d
and a d ju s te d by means o f th e v a r ia b le r e s is ta n c e s f o r th e
•nimim f i e l d
s tr e n g th t o be u sed .
4-.
The a lt e r n a t i n g c u rre n t was a d ju s te d f o r minimum v ib ra ­
t i o n o f th e sp ac e r w ire s .
5.
The g a in in w eight o f th e m a te ria l i n th e m agnetic f i e l d
was th e n found by adding w eig h ts to th e pan u n t i l a b alan ce was reach ed .
6.
W ithout in te r r u p t in g th e flow o f d ir e c t c u rre n t even mo­
m e n ta rily th e f i e l d s tre n g th was in c re a s e d by s te p s of about 1 ,0 0 0 o er­
s te d s and b a lan c e w eig h ts f o r each s te p reco rd ed u n t i l th e maximum f i e l d
s tr e n g th was reach ed .
7.
A fte r re a ch in g th e s tro n g e s t f i e l d , th e c u rre n t was de­
c re a s e d by sm all s te p s and w eighings made in th e d ir e c tio n of s tro n g to
weak f i e l d s .
The magnet was not tu r n e d o f f from th e tim e th e v ir g in
curve was determ ined u n t i l th e He was found.
8.
A fte r w eighing i n th e w eakest f i e l d th e c u rre n t was r e ­
duced to zero and th e p o l a r i t y of th e magnet re v e rse d by means o f a
re v e rs in g sw itch .
9.
The f i e l d s tr e n g th was th e n in c re a s e d (now i n re v e rse
d ir e c tio n to th e o r ig i n a l m agnetizing fo rc e ) u n t i l th e m a te ria l showed
a zero g a in i n w e ig h t.
At t h i s p o in t
U
k H = 0 and, th e r e f o r e , t h i s
was th e opposing f i e l d w hich reduced th e remanence to z e ro .
By d e f i­
n i t i o n t h i s i s th e c o e rc iv e fo rc e Hq.
10.
F ie ld s tre n g th s were in c re a s e d once more and w eighings
made up to th e maximum f i e l d u sed .
S teps 7 , 8 , and 9 w ere’ re p e a te d
29
t o o b ta in d a ta f o r th e low er s id e of th e h y s te r e s is loop ( t h i r d ,
f o u r th , and f i r s t q u a d ra n ts ).
11.
The tu b e was th e n em ptied and th e c o n te n ts weighed
L im ita tio n o f th e p ro c e d u re .
I t i s i n te r e s t in g to n o te t h a t v e ry
few m a te r ia ls can be an aly zed m a g n e tic a lly i n t h i s fa s h io n .
s u s c e p t i b i l i t y becomes of th e o rd e r o f
2
I f th e
x 10 ”^ in f i e l d s tr e n g th s
above 3>000 o r 4 >00 Q o e rs te d s , th e s id e a t t r a c t i o n of th e magnet fa c e s
becomes to o g r e a t to be c o u n te ra c te d by th e weak fo rc e o f th e v ib r a tin g
w ire s .
A lso in a m a te ria l w ith a h ig h remanence th e tu rn in g to rq u e
o f th e m agnetized m a te ria l becomes q u ite h ig h and th e sample tu b e must
be r i g i d l y a tta c h e d to th e rod suspended from th e balan ce arm.
The
to rq u e was low f o r h e m atite and a suspension of no. 16 copper w ire
k e p t th e tu b e from tu r n in g .
As th e f i e l d s tr e n g th s in c re a s e , th e b a l­
ance p o in t becomes h a rd e r to f in d and, con seq u en tly , th e re i s about th e
same p r e c is io n of measurement a t h ig h and low f i e l d s .
Com putation.
A d e ta i l e d c a lc u la tio n o f one value o f 4
I i s h e re ­
w ith p re s e n te d .
L a ta :
Ammeter read in g
Gain i n w eight
Sample w eight
Length of sample
D ensity of sample
2 .0 0 amperes
355
mg.
7.03 g.
1
An ammeter read in g o f 2.00 amperes in d ic a te s a f i e l d s tr e n g th
o f 3 ,3 4 0 o e rs te d s (f ig u re 4 ) .
30
S olving f o r X :
g
Xg = 2 x le n g th x g a in in -weight
o r ig i n a l w eight of m a te ria l x
x 1 .0 1 9
s 2 x 1 1 .7 * 355
7.03 x (5340r x 1.019
X = 4 0 .7 x 10 -6
g
Volume s u s c e p t i b i l i t y (k) - X x ap p aren t d e n s ity
k
= 4 0 .7 x 2.15 = 87.4
4 n k H= 4 n I
4 ^ I
= 12.57 x 87 .4 x 5340 = 5 .8 8 g a u sse s.
A h y s te r e s is loop can th e n be drawn by p lo ttin g a s e r ie s o f
4 "frI v a lu e s a g a in s t th e corresponding v a lu e s o f H.
C oercive f o rce v a lu es a re o b ta in e d d i r e c t l y from th e exper­
im e n ta l d a ta w hereas Br v a lu e s must be in te r p o la te d from th e h y s te r e s is
lo o p s .
R e s u lts .
Tables I I I to IX, in c lu s iv e , c o n ta in th e s u s c e p tib ili ty
d a ta f o r Cumberland h e m a tite ; ta b le X th a t f o r C. P. F e r r ic Oxide; XI
to XIV, in c lu s iv e , th e d a ta f o r M ichigan h em atite no. 1, and s im ila r
m a te r ia l f o r M ichigan h em atite no. 2 i s shown in ta b le XV.
In most cases th e low er h a lf o f th e h y s te r e s is loop was drawn
by symmetry.
No p o in ts a re shown in th e second quadrant of th e h y s te r e s is
lo o p s f o r th e re a so n t h a t i t was found time-consuming to o b ta in n ecessary
d a ta f o r such p o in ts .
Such a procedure i s p e r f e c tly v a lid sin c e th e Hc
and Bp v a lu e s a re independent o f th e shape of th e curve in th e second
q u a d ra n t.
Tables XVI and XVII summarize most of th e He and Br d a ta found
i n ta b le s I I I to XV, in c lu s iv e .
31
T ables XVIII and X U c o n ta in r e s u l t s o b ta in e d on th e C u rie ty p e b a la n c e .
F ig u re 5 i s a g ra p h ic a l r e p re s e n ta tio n o f th e r e s u l t s in
ta b le I I I , f ig u r e 6 t h a t of t a b l e
IV, and f ig u r e 7 th a t of ta b le V II.
F ig u re 8 p re s e n ts th e r e s u l t s o f ta b l e X II,
change i n s u s c e p t i b i l i t y and Hc as H changes.
F ig u re 9 shows
F ig u res 10 and 11 show
g ra p h ic a lly th e Hc and Br d a ta given in ta b le XVI and XVII.
The curves i n f ig u r e 10 should be co n sid ered as in d ic a tiv e
of th e p ro b ab le change o f Hc w ith p a r tic l e size#
Such re s e a rc h was
r e a l l y n o t p e r tin e n t t o th e problem and th e la b o r in v o lv ed in p re p a r­
in g numerous, c a r e f u lly s iz e d f r a c tio n s i n o rd e r to o b ta in a b so lu te
r e s u l t s was n o t ju s tif ie d #
F ig u re 12 shows th e change i n s u s c e p t i b i l i t y o f a h em atite
a s i t i s h e a te d and th e n co o led in a magnetic f i e l d .
F ig u re 13 con­
t a i n s h y s te r e s is curves b e fo re and a f t e r h e a tin g th e same hem atite#
32
TABLE I I I
S u s c e p t i b i l i t y d a t a f o r C u m b erlan d h e m a t i t e
S iz e
Weight
Length
D en sity
0-5
3.537
11.7
1.1 3
m icrons
grams
cm.
gms./cm3
H2 2 10-6 .
Gain (mg.)
X x 106 :
g
.
610
1310
2040
3390
5410
6910
8000
.377
1.72
4.16
11.5
29.3
4 7 .8
6 4 .0
4
20
48
131
333
458
603
69.0
75.6
75.0
74.0
73.9
63 .7
6 1 .2
♦60
1 .5 1
2.1 8
3.56
5.67
6.2 5
6 .9 6
6910
5410
3390
2090
1310
614
47 .8
29.3
H .5
4.16
1.7 2
.377
498
353
193
100
57
23
67 .7
78.3
109
156
215
397
6 .6 4
6 .0 1
5.25
4.51
4 .0 0
3.47
2235
3390
5410
6910
8000
n .5
2 9 .3
4.7 .8
6 4 .0
0
67
258
4-53
583
0
37.9
57.2
6 1.7
59.2
0
1.82
4.40
6.05
6.73
6910
5ao
3390
204.0
1310
614.
47 .8
29.3
11.5
4.16
1.7 2
.377
503
350
193
102
56
23
6 7 .8
78.2
109
159
210
397
6 .6 8
5.98
5.25
4.57
3.95
3.47
11.5
29.3
4 7 .8
6 4 .O
0
65
266
441
603
0
37.5
58.7
6 1 .6
6 1 .2
0
1.7 8
4.5 1
6 .0 1
6 .9 6
H :
4 m
R everse
R everse
2235
3390
5410
6910
8000
33
TABLE IV
S u s c e p t i b i l i t y d a t a f o r C u m b erlan d h e m a t i t e
S ize
Weight
Length
D en sity
H
10- 6
H2 x- ~
0-5
7*307
11*7
2*30
Gain (mg.)
X x 106
g
4 “^ !
66.3
73.0
7 1 .4
71.4
69.1
6 4 .8
61.9
I .23
2.g2
4 .2 1
7.06
10.8
12.9
14.3
69.1
78 .7
112
13.8
12.3
11.0
8.72
8.34
7.30
614
1310
2040
3390
5410
6910
8000
11.5
29.3
47 .8
6 4 .O
8
40
93
261
643
983
1258
6910
5410
3390
2040
1310
614
4 7 .8
29.3
11.5
4.16
1.72
.377
1048
733
409
207
119
49
2235
3390
5410
6910
8000
11.5
29.3
47.8
64.0
0
140
527
910
1238
6910
5410
3390
2040
1310
614
4 7 .8
29.3
11.5
4.16
1.72
.377
1035
720
401
205
117
48
.377
1.72
4.16
m icrons
grams
cm.
gms./cm?
148
218
409
R everse
38.3
5 6 .6
60.0
60.9
0
3.75
8 .8 4
12.0
1 4 .1
68.8
13.6
78.4
108
143
213
400
12.1
10.9
8.67
8.05
7.17
34TABLE V
S u s c e p t i b i l i t y d a t a f o r C u m b erlan d h e m a t i t e
S iz e
W eight
Length
D en sity
H
:
H2 x 10~6 :
5-10
4*.063
11*7
1*28
Gain (mg.)
m icrons
grains
cm*
gms./cm^
xg x 106
4 IT I
614
1310
20 A0
3390
54-10
6910
8000
♦377
1.72
4 .1 6
11.5
29.3
47 .8
6 4 .O
21
184
168
393
792
1141
1417
365
286
229
193
153
135
125
3.11
6 .0 3
7.51
10.5
13.2
1 5 .0
1 6 .1
6910
5410
3390
2040
1310
614
4 7 .8
29.3
11.5
4 .1 6
1.72
.377
1202
847
453
231
132
45
143
169
223
314
434
683
15.9
14.3
1 2 .1
1 0 .3
9 .2
6 .7
580
1310
2040
3390
5410
6910
8000
1.72
4 .1 6
11.5
29.3
47 .8
64 .O
0
43
124
33S
707
1037
1347
0
142
169
166
136
123
119
0
3 .0 0
5.53
9.03
1 1 .8
13.6
15.3
6910
5410
3390
2040
1310
614
47 .8
29.3
11.5
4 .1 6
1.72
.377
1142
797
43 4221
124
40
135
154
204
300
408
616
15.0
13 .4
1 1 .1
9.8 4
8 .6 0
6.08
1.72
4.16
11.5
29.3
0
60
138
364
775
0
197
188
179
149
0
4.15
6.18
9.76
13.0
R everse
Reverse
580
1310
2040
3390
5410
TABLE V I
35
S u s c e p t i b i l i t y d a ta f o r Cumberland h e m a tite
S iz e
h e ig h t
Length
D en sity
H
:
614
1310
2040
1310
614
R everse
200
614
1310
2040
Reverse
3390
5410
3390
2040
1310
614
Reverse
1250
2040
3390
5410
R everse
6910
8000
6910
5410
3390
2040
1310
614
Reverse
I 63 O
2040
3390
5410
6910
8000
H2 x 10-6
10-20
S .751
11.7
2.76
;
m icrons
grams
cm,
gms./cm^
Gain (mg.) :
Xg x 10^
4 TTI
.377
1.7 2
4.1 6
1 .7 2
.377
13
65
143
71
22
90.6
9 9 .4
88.0
108
153
1.93
4 .51
6.2 1
4.9 2
3.26
.377
1.72
4.16
0
11
55
136
0
80.1
84.0
85.9
0
1.70
3.80
6.08
11.5
29.3
11.5
4.16
1 .7 2
.377
360
903
469
234
124
42
82.3
81.0
107
148
189
293
9 .72
15.2
12.6
10.5
8.67
6.22
4 .1 6
11.5
29.3
0
87
351
909
0
55.0
80.2
81.5
0
3 .9 4
9.40
15.3
47.8
64.0
47 .8
29.3
11.5
4.16
1.72
.377
1469
1829
1484
1029
526
263
149
55
80.8
7 5 .1
81.7
92.3
120
166
228
383
1 9 .4
20.8
19.5
18.7
14.1
11.7
10.3
8.11
4.1 6
11.5
29.3
4 7 .8
64.0
0
64
283
830
1369
1799
0
4 0 .4
64.7
74 .4
75.3
73.9
0
2.8 4
7.62
13.9
18.0
20,5
36
TABLE V I I
S u s c e p t i b i l i t y d a t a f o r C u m b erlan d h e m a t i t e
S iz e
Weight
Length
D en sity
H
:
H2 x 10“°
:
20-40
9.929
1 1 .7
3.13
Gain (mg)
m icrons
grams
cm.
gms./cm^
Xg x 106
4
I
614
1310
2040
3390
5410
6910
8000
.377
1 .7 2
4 .1 6
H .5
29.3
4 7 .8
6 4 .O
13
66
154
434
1066
1556
1991
81.2
88 .8
85.5
87.4
84.5
7 5 .4
72.0
1.96
4 .5 8
6.85
H .6
18.0
20.5
22.6
6910
5410
3390
2040
1310
614
4 7 .8
29.3
11.5
4.16
1.7 2
.377
1611
1131
595
308
171
64
7 8 .1
89.4
120
171
230
393
21.2
19.0
1 6 .2
1 3 .7
1 1 .8
9 .5
R everse
1560
2040
3390
5410
6910
8000
4.16
11.5
29.3
4B.7
64*0
0
48
307
951
1411
1881
6910
5410
3390
2040
1310
614
48.7
29.3
11.5
4.16
1.72
.377
1501
1101
566
288
161
61
72.8
87.0
114
161
217
375
1 9 .8
18.5
15.2
12.9
11.2
9.05
R everse
1560
2040
3390
5410
6910
8000
4.16
11.5
29.3
4 8 .7
6 4 .O
0
73
358
988
15a
1991
0
40.6
72.1
78.1
74.7
72.0
0
3.26
9.60
1 6 .6
20.3
22.6
0
26 .7
61.8
75 .1
6 8 .4
68.0 ,
0
2.1 4
8.22
1 6 .0
1 8 .6
21.4
37
TABLE V I I I
S u s c e p t i b i l i t y d a t a f o r C um berland h e m a t i t e
S iz e
W eight
Length
D en sity
H
:
H2 x 10
-6
:
40-74
11.191
1 1 .7
3.52
Gain (mg.)
m icrons
grams
cm.
~
gms./cm
Xg x 106
•
4 TTI
•
•
644
1330
2050
3440
5320
6940
7920
.415
1.76
4.2 0
1 1 .8
28.3
48.2
62 .7
12
53
139
420
1095
1699
2103
5 9 .4
61.8
6 8 .1
73.2
7 9.4
72.6
6 8.8
3.54
3 .6 4
6.17
11.1
18 .7
22.3
24 .1
6940
5320
3440
2050
1330
644
48 .2
28.3
1 1 .8
4.20
1.76
.415
1790
1253
651
330
190
76
7 6 .4
91 .0
113
161
218
363
23.4
21 .4
17.2
14.6
12.8
10.3
1300
2050
3440
5320
6940
7920
4.20
11.8
28.3
48.2
6 2 .7
0
39
347
984
1539
2019
0
1 9.1
6 0.4
71.5
68.5
66.2
0
2.74
9.20
16 .8
21.0
2 3 .2
6940
5320
3440
2050
1330
644
48.2
28.3
1 1 .8
4 .2 0
1.76
.415
1619
1174
633
309
175
69
69.0
85.2
110
151
203
341
21.2
20.0
16 .8
13 .1
11.9
9 .7 2
0
0
0
R everse
Reverse
1300
38
TABLE I I
S u s c e p t i b i l i t y d a ta f o r Cumberland h e m atite
S iz e
Weight
Length
D en sity
H
:
W1
x 10-6
*:
591-1652
11.553
11.7
■ 3 .6 4
Gain (mg.)
m icrons
grams
cm.
gms./cm^
g
x 106
644
2090
5120
8170
.415
4 .3 7
29*3
66.9
12
120
977
2017
57.5
54.8
6 6 .2
6 0 .0
5420
2090
644-
29*3
4 .3 7
.415
1115
323
73
75.6
147
350
1200
3440
5420
8170
1 1 .8
29.3
66.9
0
217
801
1967
0
3 6 .6
5 4.4
58.4
5420
3440
2090
644
29.3
1 1 .8
4 .3 7
.415
1007
513
274
72
68.3
8 6.3
125
341
R everse
1200
3440
5420
8170
1 1 .8
29.3
66.9
0
307
907
1977
0
5 2 .8
6 1 .4
59.0
4 tti
1 .6 8
5 .2 4
16 .4
22.4
1 8 .7
1 2 .7
10.3
R everse
0
5.82
13.7
21.7
16.9
13.5
1 0 .8
1 0 .4
0
8.33
15.7
22.3
39
TABLE X
S u s c e p t i b i l i t y d a ta f o r C .P . f e r r i c o x id e
P r e c ip ita te d
Weight
Length
D en sity
H
357
984
1670
2425
3210
5220
6385
6952
7500
8150
8794
9484
8880
8110
7630
7080
6510
5270
3490
2690
1940
1270
525
H2 x 10*"6
Fe 203
3*096 grams
1 1 .7
cm.
.975 gms./cm^
Gain (mg.)
x 106
.127
.9 6 8
2 . SO
5 .8 8
10.3
27.3
40. 8
48.3
56.3
6 6 .4
77.3
89.9
78 .6
6 5 .8
5 8 .2
5 0 .1
4 2 .4
2 7 .8
1 2 .2
7 .2 4
3.76
1 .6 1
.276
1
10
30
64
110
274
364
424
489
534
615
705
639
555
515
458
406
317
174
120
78
46
17
58.5
76.0
7 9 .4
80.9
79.3
74.7
6 6 .7
65.2
64.5
59.7
6 2 .0
58.3
6 O.4
6 2.7
65.7
67.9
71.2
84.7
129
123
154
212
458
5 .6 6
1 1 .0
30.3
i
5 0 .8
59*9
6 7 .4
80.1
89.9
0
27
80
264
337
408
483
517
624
705
0
35.4
54.0
6 4 .8
60.9
59.6
59.9
5 6.6
57.9
58.3
.256
.917
1.63
2.41
3.12
4 .7 8
5 .2 2
5 .5 6
5.93
5.96
6 .6 8
6 .7 8
6.67
6.23
6.15
5.39
5 .6 8
5.47
5.52
4 .0 6
3 .6 6
3.30
2.95
R everse
2010
2380
3320
5500
6410
7130
7740
8210
8950
9480
0
1.03
2.19
4.50
4.79
5.21
5 .6 8
5.70
6.35
6.78
TABLE X I
S u s c e p t i b i l i t y and Hv d a ta f o r M ichigan h e m atite no. 1
S iz e
Weight
Length
D e n sity
H
:
575
910
1230
2990
4150
5340
6550
7120
8670
9880
8680
7260
6580
5560
4320
3200
2310
1610
910
H2 x 10"6
.
0-5
7.03
1 1 .7
2.15
Gain (mg.)
m icrons
grams
cm.
gms./cm?
: Xg x 106
:
4 tt I
.330
*825
1 .5 2
8.97
17.2
28.5
4 2 .8
51.4
75.0
97.5
75 .1
52 .8
43 .2
3 0 .8
18.6
10.2
5.33
2.59
.825
5
13
25
127
227
355
510
615
850
1070
880
700
610
475
355
207
138
87
42
49.5
51.5
53.8
46.3
43.2
40.7
38.9
34.2
37.0
35.9
38.3
43.3
45.5
50 .3
62.3
66.5
84.5
110
167
.770
1 .2 3
1.79
3.75
4 .8 5
5.88
6.92
7.65
8.70
9.62
9.05
8.55
8.13
7.53
7.28
5.77
5.28
4.80
3.95
8.97
17.2
28.5
4 2 .2
51.4
75.0
9 6 .1
0
38
142
345
470
56 5
830
1060
0
13.9
27.0
29.4
33.4
3 6 .0
3 6 .0
3 6 .2
0
1.13
3.03
5.72
6.42
7.04
8.50
9.6 8
Reverse
2340
2990
4150
5340
6500
7180
8670
9810
a
TABLE X I I
S u s c e p t i . b i l i t y and. H
c
d a t a f o r M ic h ig a n h e m a t i t e no* 1
S iz e
4-0 + 100
W eight 10*8
Length 1 1 .7
D e n sity
2 .9 1
H
:
H2 x 10-6
Gain (mg.)
mesh
grams
cm.
3
gms./cm
!
Xg x 106
:
4 TTI
575
1230
1960
2990
4150
5340
6550
7180
8670
9850
8680
7260
6580
5560
4320
3200
2310
1610
910
.330
1.52
3.85
8.97
17.2
28.5
4 2 .8
5 1 .4
75.0
96 .9
75 .1
52 .8
4 3 .2
3 0 .8
1 8 .6
10.2
5.33
2.59
.825
11
55
144
326
625
940
1235
1440
1890
2300
1990
1565
1360
1085
835
583
380
253
122
72 .8
76.9
79.5
77.5
77 .4
70.7
61 .4
59.7
53.7
50.6
5 6.4
6 3 .2
67 .1
75.0
95.6
122
152
208
315
1.70
3.46
5.72
8.45
11.75
13 .8
14.7
15.7
17.0
18.3
17.9
16.7
16 .1
15.2
1 5 .1
14.3
1 2 .8
12.3
10.5
R everse
2340
2990
4150
5340
6550
7180
8670
9850
8.97
1 7 .2
28.5
4 2 .8
51.4
75.0
96.9
0
108
380
705
1140
1420
1850
2300
0
25 .7
47.0
52.6
56.7
59.0
5 2 .6
5 0 .6
0
2.81
7.15
10.3
13.6
15.6
16 .6
18.3
TABLE X I I I
S u s c e p t i b i l i t y a n d Hc d a t a f o r M ic h ig a n h e m a t i t e n o . 1
W eight
S iz e
D e n sity
H
:
720
1360
2140
3110
4340'
5500
7470
8320
9920
S340
7480
5730
4380
3390
23 S0
1640
900
H2 x 10
—6
25.4- grams
3/ 8 ” x 3/8" x 4"
5 .2 gms. /cm?
Gain (mgi x 10^
T 788 x e a ln
: 4TTI
1• g
.518
1.85
4 .5 8
9 .6 7
1 8 .8
3 0 .2
55.7
68 .0
98 .2
69.3
55 .8
3 2 .7
19.2
11 .4
5.67
2.6 8
.81
28
150
405
850
1880
2820
4620
5950
7500
6070
4930
3470
2490
1785
1170
784
407
42.6
6 3 .8
69.5
69.3
78.2
73.5
65.5
68.9
60.3
69.2
69.7
83.5
102
123
163 '
232
396
2.00
5.68
9.75
14 .1
22.2
2 6.4
3 2 .0
37.5
39.2
37.7
34.1
3 0 .2
2 9 .2
27.3
25.3
2 4 .8
23.3
0
71.3
70.0
64.3
6 4 .6
6 O.3
0
18.5
3 0 .2
5 5 .7
68.0
98 .2
0
1700
2670
4430
5860
7500
R everse
2400
4310
5300
7470
8320
9920
20 .4
2 4 .8
31 .7
3 6 .8
39.2
43
TABLE XIV
S u s c e p t i b i l i t y a n d Hc d a t a f o r M ic h ig a n h e m a t i t e n o , 1
S iz e
W eight
D en sity
3/ 8 ” x 3/8" x A"
29,3 grams
5 • 2 gms. / cm-*
*
H
650
990
1150
1310
1520
1680
1860
2000
2360
2600
3040
3400
36 OO
4080
4330
4560
4750
5470
66A0
7530
:
G ain (mg,)
25
59
83
120
182
238
323
365
516
790
910
1180
1330
1620
1745
1850
2020
2620
3830
4900
:
H
c
320
460
490
630
680
850
900
990
1120
1540
1480
1700
1800
1860
1920
I960
1980
2040
2320
2320
:
X x 106
g
4 TTI
43.7
4 9 .8
51.7
57 .8
64.3
69.7
72.3
75.3
7 6.4
1 .8 6
3 .2 2
3.89
4.95
6.39
7.67
7.80
9.89
1 1 .8
81.8
8 4 .6
8 4.6
80.0
76.7
73.5
72.8
72.2
71.9
71.5
1 6 .3
1 8 .8
19.9
21.3
21.7
21.9
22.6
25.8
31.1
35.2
44
TABLE XV
S u s c e p t i b i l i t y a n d Hc d a t a f o r M ic h ig a n h e m a t i t e n o , 2
S iz e
Weight
Length
D en sity
-200
9,40
1 1 .7
2 .5 4
mesh
grams
cm.
~
gm s./cnr
*
H
:
575
1230
I960
2990
4150
5340
6430
7180
8670
9800
8680
7260
6500
5560
4320
3200
2310
1610
910
H2 x
XT6
Gain (mg.)
: Xg x 106
:
4TT I
.33 0
1.52
3.85
8.97
17.2
28.5
41.3
51 .4
75 .0
9 6 .0
75.1
52.8
42.2
3 0 .8
18 .6
10.9
5.33
2.59
.825
44
196
295
619
990
1460
1950
2270
3080
3605
3130
2510
2160
1770
1230
890
570
360
163
326
316
315
303
141
125
116
108
101
92
102
116
125
141
162
212
262
341
479
6 .0
12.4
21.0
29.0
18.7
21.4
23.8
24.8
28.0
28.8
28.3
26.9
26.0
25.1
22.4
21.9
1 9 .4
17.6
14.0
3.85
8.97
17.2
28.5
40.5
51.4
75.0
96.3
98
304
755
1380
1780
2100
3010
3530
62
83
108
119
108
100
98
91
3.90
10.6
1 4 .4
20.3
22.0
22.9
27.1
28.5
R everse
I960
2990
4150
5340
636 O
7180
8670
9820
TABLE XVI
V a ria tio n o f co erciv e fo rc e w ith g ra in s iz e
m agnetized i n f i e l d s o f 8 ,0 0 0 to 9 ,0 0 0 o e rs te d s
Cumberland h e m a tite
G rain s iz e ,
m icrons
Hc>
o e rs te d s
2240
0 -5
580
5-10
20
1630
20 - 40
1560
40 - 74
1300
74 - 592
1225
592 - 1650
1200
10
-
M ichigan h e m a tite no. 1
S ize
0 - 5
m icrons
2340
-4 0 +100 mesh
2340
mesh
2340
-200
S o lid b lo ck
2400
M ichigan h e m a tite n o . 2
S iz e
h
-200 mesh
1400
-4 0 + 100
1140
-28 + 100
1140
c . P . f e r r i c oxide
S ize
P r e c ip it a t e d
He
2010
46
V a ria tio n o f remanence w ith packing d e n s ity .
Cumberland h e m atite m agnetized in f i e l d s of
approxim ately 8,000 o e rs te d s
G rain s iz e ,
m icrons
2.1
0 - 5
1.28
4.0
5-10
2.30
5*8
0 - 5
2.76
6.5
10 - 20
3.13
7.3
3.52
8.0
40 - 74
3.64
8.0
592 - 1650
£
1.13
?o
0
1
Packing d e n s i t y ,: Bp,
gnn/cm.3
: gauss
47
TABLE X V III
Them om agnetic d a ta f o r Cumberland h e m atite
0 - 5 m icrons
•
Temp*
° C.
:
:
B alance c u r r e n t, :
m illian rp eres
:
18
100
200
300
410
500
555
590
660
693
720
47
47
48
49
50
53
53
47
39
27
27
695
682
668
615
555
510
420
300
100
18
27
36
41
48
50
50
50
50
50
50
X x 106
g
22
45
48
TABLE XIX
Thermomagnetic d a ta f o r Cumberland h em atite
0 - 5 m icrons
O rig in a l loop
: A fte r co o lin g in magnetic
H in
: B alance
:
f i e l d from C urie p o in t
o e rs te d s : c u rre n t______ :H in o e rs te d s : Balance c u rre n t
1600
2350
3100
3850
4640
5270
5840
6320
7020
7900
8360
8920
7900
5840
4640
3100
1600
Reverse
2350
3100
4640
5840
7020
7900
8920
7900
5840
4640
3100
1600
Reverse
2350
3100
4640
5840
7020
7900
8920
9
15
21
27
31
34
40
1600
2350
3100
3850
4640
5270
6320
20
24
29
34
38
43
48
Reverse
3850
4640
5270
5840
7020
10
18
24
31
43
47
54
57
60
55
44
36
28
16
3
9
23
34
45
52
60
55
44
36
28
16
4
9
23
34
45
52
60
8920
6320
5270
4640
3850
3100
2350
1600
Reverse
3850
4640
5270
5840
7020
8920
60
48
43
38
34
29
24
20
10
18
24
31
43
60
10,000
FIELD STRENGTH, H IN OERSTEDS
8,000
6,000
■o Increasing c u rre n t
D ecreasing cu rre n t
4,000
2,000
CURRENT I, AMPERES
Figure 4
• — Ma g n e t
calibration.
/W* 3
,
-periy
ot
ilia
BUREAU OF M IN E S
d e p a r t m e n t of the interior
Net to be us e ^ tor any pu r p o s e
without sui tabl e acknowledg
men t
co
UJ
CO
CO
Size, 0 - 5 microns
Density, 1.13 grams
per cubic centimeters
8,000
0
4,000
4,000
8,000
H IN OERSTEDS
Figure
S
.— Susceptibility
densi ty
data
1.13.
for
the Cumberland h e m a t i t e ,
size 0-5 microns,
P ro p erty of th e
Size, 0 - 5 microns
Density, 2.30 grams
per cubic centimeters
8,000
Figure
6
4,000
.—Susceptibility
0
H IN OERSTEDS
data
densi ty 2 .30 .
for
t he Cumberland
4,000
8,000
^
^
hematite
size
0-5 microns,
Property gi die
7; W
■E A U O r MSNFS
0 i Or ; WF I N [ T R I O
; i'sec ior nr ' Durrnse
' ••
. c:vv cds msnt
CO
CO
CO
Size, 20 -4 0 microns
Density, 3.13 grams
per cubic centimeters
8,000
Figure
T
■
4,000
S u s c e p t i b i l i t y
data
0
H IN OERSTEDS
for
the
Cumberland
4,000
hem at ite,
8,000
size
20-40 microns.
o
cS
CO
LlI
CO
CO
o 0
Size, 40+100 mesh
Density, 2.91 grams
per cubic centimeters
8,000
4,000
0
H IN OERSTEDS
Fi gu r e
4,000
8,000
P operty ot the
dU R E A U OF M IN E S
D E P A R T M E N T 0 r TH E INTERIO R
Not t o b e used for uny p u r p e s e
s u i t a b l e a c k n o w i e d e ro*nt
SUSCEPTIBILITY, X g x lO 5
COERCIVE FORCE, Hc IN GAUSSES
3,000
2,000
1,000
Natural Michigan hematite No. 1
Density 5.2grams per cubic centimeters
2,000
Figure
9
4,000
FIELD STRENGTH, H IN OERSTEDS
. — Ferromagnetic
(a)
ship
curve
for hematite
Ferromagnetic curve
for
between m a g n e t i z a t i o n
and
6,000
relationship.
hematite,
(b)
Relation­
and d e m a g n e t i z a t i o n
forces.
sU R E A U OF M IN ES
O E P A R T M E N T O F T H E INTERIO R
N et t c b e u sed for any p u rp o se
w ith o u t su ita b le acknow iedg
f
f
lS
O
t
2,500
COERCIVE FORCE, HC IN GAUSSES
Michigan hematite No. 1
2,000
1,500
1,000
2,000
3,000
1,000
100 4 )
SPECIFIC SURFACE (AS RECIPROCAL MICRONS x* 1
Figure
IO . — R e l a t i o n
between
specific
surface
and
coercive
forces,
4,000
M-3
Property of the
BUREAU OF M IN ES
D E P A R T M E N T O F THE INTERIOR
N e t to be u s ed for any pu rp ose
w i t h e u t su itab ie acknowlerlg
GO
< c
CD 6
zLLl 4
z
c
UJ
oc
PACKING DENSITY* GRAMS PER CUBIC CENTIMETERS
M-3
.5 0
Figure
density
II
and
•— Relationship
between
packing
r emanence o f Cumberland h e m a t i t e .
P ro p erty of th e
BUREAU OF M IN ES
D E P A R T M E N T O F THE INTERIO R
to be u s e d for any o u r p e s e
Without suitable auk/inwbdg (r*snt
[2 6 0
ce
LU
CL
ID
-O
o
o-
—Q"
35 g
x\
o
GO
CO
I—
CL
LU
LEGEND
x-------- x Increasing temperature
o ---------o Decreasing temperature
O
CO
■X—
LU
200
400
TEMPERATURE, °C.
600
800
A l-3
Figure
/2
S3
• — Thermomagnetic c u r v e
size
0-5 microns.
for
t h e Cumb e r l a n d h e m a t i t e
H= 7 , 0 0 0 o e r s t e d s .
Property
mum
BUREAU O F
D E P A R T M E N T OF T H E I N T E ^ p R
Nat to be used for any purpase
w ithou t su ita b le acknow ledg m ent
MAGNETIC BALANCE
CURRENT, MILLIAMPERES
Cumberland hematite
Size, 0 - 5 microns
10,000
8,000
6,000
4,000
2,000
2,000
H, IN OERSTEDS
4 ,0 0 0
6,000
8 ,0 0 0
10,000
A
7-3
S/
Figure
1
3 .— Effect
on h y s t e r e s i s
point
loop o f
in a m a g n e t i c
field.
cooling
hematite
f rom i t s
Curie
Property of
the
BUREAU OF MINES
DEPARTM ENT OF THE INTERIOR
Not to be used for any pMrfftff?
without suitable acknowledg fn»nt
49
DISCUSSION OF RESULTS
S u s c e p tib ility .
The fe rro m ag n etic n a tu re o f h e m atite may be
deduced from th e shape o f th e s u s c e p t i b i l i t y v s . f i e l d s tre n g th curves*
Most o f th e pure h e m atite f r a c tio n s used had a range o f s u s c e p t i b i l i t y
v a lu e s o f Xg = 40 to 100 x 10”^ , w hile some o f th e m a g n e tic a lly con­
ta m in a te d h e m a tite s showed s u s c e p t i b i l i t y v alu es as high as 300 x 10—6
i n f i e l d s below 2,000 o e rs te d s .
60 x 10
—6
Most o f th e Xg v a lu es a re from 40 to
i n th e low er f i e l d s and th e s e agree s u b s ta n tia lly w ith th e
r e s u l t s o f o th e r in v e s t ig a to r s .
Most w orkers in t h i s f i e l d have ten d ed
to re g a rd h e m atite as p a ra m a g n e tic ^ and th e re fo re u s u a lly only one
s u s c e p t i b i l i t y v alu e p e r sample i s quoted in th e l i t e r a t u r e .
This s in g le
v a lu e was computed from measurements a t com paratively low f i e l d s o f 400
to 700 o e rs te d s and hence pro v id es o n ly a rough check on th e s u s c e p ti­
b i l i t y v a lu es determ ined In t h i s in v e s tig a ti o n .
The d a ta in ta b le s I I I
to X7I in d ic a te t h a t th e maximum s u s c e p t i b i l i t y o f pure h em atite occurs
in f i e l d s ran g in g from 1 ,5 0 0 to 3,500 o e rs te d s , w ith a p r o b a b ility th a t
th e h ig h e r f ig u r e i s more n e a rly c o rre c t as th e fo llo w in g c o n sid e ra tio n s
show.
A ccording to G o ttsch alk ‘d th e maximum s u s c e p tib ili ty of m agnetite
45
i s a tta in e d i n f i e l d s le s s th a n 13 o e rs te d s , w h ile D avis1 r e s u l t s show
t h a t th e maximum s u s c e p t i b i l i t y f o r gamma h em atite i s found in f i e l d s
l e s s th a n 6 o e rs te d s .
The presen ce of e it h e r Fe304 o r gamma Fe203 in
^ A param agnetic substan ce i s one whose s u s c e p t i b i l i t y does not
change w ith f i e l d s tr e n g th .
44
See fo o tn o te 25d.
^ C. W. D avis. M agnetic P r o p e r tie s o f M inerals and T heir Sig­
n if ic a n c e . R eport of In v e s tig a tio n s 3268, Bureau of M ines, p . 93*
50
a h e m a tite would te n d to make th e maximum occur a t low er f i e l d s and
would s h i f t th e upper curve i n f ig u r e 9 to th e l e f t .
That t h i s f a c t
o f f e r s a means of determ inin g m agnetic im p u ritie s i n sm all amounts
i s w e ll shown i n th e r e s u l t s i n t a b l e XV.
The s u s c e p t i b i l i t i e s de­
te rm in e d f o r t h i s h e m atite a r e a l l h ig h and, as m ight be expected,
th e maximum p e rm e a b ility occurs a t a low f i e l d s tre n g th somewhere be­
low 600 o e r s te d s , in d ic a tin g th e presence of Fe 304 o r gamma hem atite
i n a p p re c ia b le am ounts.
Although t h i s method o f d eterm in atio n o f
m agnetic im p u r itie s could undoubtedly be worked o u t in g r e a te r d e t a i l ,
i t i s u n fo rtu n a te t h a t i t does n o t d i f f e r e n t i a t e between amounts of
th e d i f f e r e n t m agnetic c o n s titu e n ts .
I n e f f e c t Benard advocates t h i s
same p r in c ip le to show th e presence of Fe304 in F e O .^
I t i s th e r e f o r e q u ite probable th a t pure h em atite has a
maximum s u s c e p t i b i l i t y i n th e neighborhood of 3*500 o e rs te d s and t h a t
sm all amounts o f m agnetic im p u ritie s ra p id ly s h i f t t h i s maximum to
lower- f i e l d s .
The peak in s u s c e p ti b i lity a t such high f i e l d s shows
h e m atite to be fe rro m ag n etic because o th e r p o s s ib le m agnetic impur­
i t i e s have long s in c e p assed t h e i r p o in ts o f maximum in t e n s i t y of
m a g n e tiz a tio n .
rn
C h e v a lie r and Mathew
have in v e s tig a te d th e v a r ia tio n of
s u s c e p t i b i l i t y w ith g ra in s iz e and found t h a t as th e g ra in s iz e de­
c re a s e s , th e s u s c e p t i b i l i t y decreases*
At 500 microns t h e i r h em atites
^ Jacques Benard. Etude de l a Decomposition du Protoxyde de
F e r e t des ses S o lu tio n S o lid e s . Annales de Chunie, 12, 1939* p . 19.
47 Raymond C h ev alier and I d l e . Suzanne Mathew. V a ria tio n o f
th e M agnetic S u s c e p ti b ility o f H em atite Powders as a F unction o f th e
S ize of th e G rain s. C. R. 204, 1937, pp. S54-856.
51
had a susc e p t i b i l i t y o f 4-00 x 10
and n e a r 0 m icron about 30 x 10”° .
Even excluding e x p erim en tal e r r o r , th e s u s c e p t i b i l i t i e s o f th e v a r­
io u s Cumberland h e m a tite s shown in ta b le s I I I to X in d ic a te no such
v a ria tio n .
There a re two p o s s i b i l i t i e s t h a t m ight account f o r t h i s
d iscrep a n c y :
( l ) C h ev alier may have used a v ery impure h e m atite, as
in d ic a te d by h ig h i n i t i a l s u s c e p t i b i l i t i e s , o r (2) th e work may have
been perform ed a t such low f i e l d s t r e n g th s , say 4.00 to 600 o e rs te d s ,
t h a t th e v a r ia tio n s would n o t be a p p re c ia b le In th e f i e l d s used in
t h i s work.
N e ith e r o f th e s e e x p lan a tio n s i s v e ry probable and th e
whole problem may be summed up i n C h e v a lie r’s words:
L’o rig in e de c e tt e d im in u tio n de s u s c e p t i b i l i t e
avec l a t a i l l e des g ra in s r e s te inconnue.
H y ste re s is lo o p s .
The h y s te r e s is loops f o r h em atite a re unique
and p ro b ab ly w ith o u t p a r a l l e l in ferrom agnetism —a t l e a s t as f a r as
th e p re s e n t knowledge of th e w r ite r i s concerned.
These curves were
p lo tte d a s H v s . 4 ft I because a B-H p lo t would be m eaningless.
The
4. IT I term i s so sm all compared to H th a t a B—II curve would be p r a c ti c a lly
a s t r a i g h t l i n e in c lin e d a t 45° p a ssin g through th e o r ig in .
s c a le been used f o r bo th H and 4
w ith th e H a x is .
I? bhe cruve
would
Had th e same
have alm ost c o in -
The s c a le s were chosen to b rin g out th e h y s te r e s is
phenomena most c l e a r l y .
In p l o tt in g h y s te r e s is curves f o r th e o rd in a ry
fe rro m ag n e tic su b stan ces H i s sm all compared w ith 4 77 I and g e n e ra lly
can be n e g le c te d .
The v a lu es o f 4 H I and E f o r h em atite a re alm ost
c
o p p o site i n magnitude to th o se of m e ta llic ferro m ag n etics f o r which th e
r e s id u a l magnetism may be s e v e ra l thousand gausses when m agnetized in
f i e l d s of le s s th a n 15 o e rs te d s .
52
The nri.de d iffe re n c e i n s c a le s u sed f o r 4 7T I and H make
i t somewhat d i f f i c u l t to a s c e r ta in w hether h e m atite i s approaching
s a tu r a tio n in f i e l d s of 8,000 to 10,000 o e rs te d s .
An a n a ly s is o f
th e c o e rc iv e f o r c e s , however, in d ic a te s th a t a t th e s e f i e l d s tre n g th s
th e h e m atite was n e a r s a tu r a ti o n .
The e x iste n c e o f a ferro m ag n etic
su b stan ce having th e com bination o f a co erciv e fo rc e of 1,100 to 2,400
o e rs te d s w ith th e v ery low remanence o f 3 to 12 gausses su g g ests th e
d e s i r a b i l i t y of a more p re c is e d e f in itio n o f ferrom agnetism .
The u su a l
tre a tm e n t of ferrom agnetism alm ost in v a r ia b ly emphasizes th e h ig h e r
degree o f m agnetic e f f e c t as compared w ith param agnetism .
But th e
s u s c e p t i b i l i t y o f h em atite i s n o t u n u su ally hig h sin c e a few su b stan ces
o f mass s u s c e p t i b i l i t y as hig h as 300
x
10“^ a re known, so t h a t in th e
p re s e n t in s ta n c e we a re d e a lin g w ith a ferro m ag n etic in th e range of
s u s c e p t i b i l i t y v a lu e s u s u a lly a ssig n e d to p aram ag n etics.
A d e f in itio n
o f ferrom agnetism t h a t would in clu d e h em atite and a t th e same tim e would
d e s c rib e th e s a l i e n t c h a r a c te r is ti c s of th e commoner ferro m ag n etic sub­
s ta n c e s should be based on th e f a c t t h a t only ferro m ag n etic su b stan ces
e x h ib it th e phenomena of r e s id u a l magnetism and co erciv e fo r c e ; t h a t i s ,
a ferro m ag n e tic su b stan ce i s one th a t r e ta in s some r e s id u a l magnetism
a f t e r th e m agnetizing fo rc e i s removed and th a t re q u ire s a d e f in ite co­
e rc iv e fo rc e to reduce t h i s re s id u a l magnetism to z e ro .
This d e f in itio n
would in c lu d e w eakly ferro m ag n etic m a te ria l l i k e h em atite o r c e r ta in
48
Cu-Iin a llo y s .
^ Some Cu-Mn a llo y s s tu d ie d by th e au th o r showed a range in Xg
rangin g from 10 x 10“^ to 200 x 10“ in f i e l d s from 3OO to 2,000 o e rs te d s .
The Xg v s , H curve shows such a llo y s to be fe rro m a g n e tic .
53
The a re a o f th e h y s te r e s is loop i s la r g e ly c o n tro lle d by th e
packing d e n s ity a s shown in f ig u r e s 5 and 6, is/here th e d e n sity was th e
o n ly v a r ia b le .
Remanence.
The v a lu e s o f r e s id u a l magnetism o b ta in e d f o r h em atite
on m agnetizing i n f i e l d s o f 8000 to 10000 o e rs te d s v ary from 2 to 12
g a u sse s.
T his extrem ely low remanence in d ic a te s th e d i f f i c u l t y o f de­
te rm in in g th e m agnetic p r o p e r tie s o f h e m a tite , and e x p la in s s u f f i c i e n t l y
th e incom plete s t a t e of our p re s e n t knowledge o f th e ferro m ag n etic na­
tu r e o f h e m a tite .
The u s u a l m agnetic measurements a re not v ery a c c u ra te
when th e p e rm e a b ility i s le s s th a n 1 .1 and th e magnetometer i s n o t very
u s e f u l a t p e rm e a b ilitie s l e s s th a n 1.003.
A r o ta tin g c o i l method might
have been used to measure t h i s remanence b u t an in stru m en t d e lic a te
enough to r e g i s t e r such low v alu es of in te n s it y o f m ag n etizatio n could
n o t be used in f i e l d s o f th e o rd e r of 1100 to 2400 o e rste d s needed to
reduce th e m ag n etiza tio n to z e ro .
F ig u re 11 shows t h a t th e remanence i s a d ir e c t fu n c tio n of
th e packing d e n s ity , b e arin g out th e w e ll known f a c t t h a t th e volume
s u s c e p t i b i l i t y k = mas6 s u s c e p t i b i l i t y , Xg, x ap p aren t d e n s ity o f ma­
t e r i a l te s te d .
S lig h t d e v ia tio n s a re due to im p u ritie s and e rro rs
i n in te r p o la tio n o f th e p o in t where th e h y s te r e s is curve c ro sse s th e
4. TTI a x i s .
This low remanence i s an o th er in d ic a tio n t h a t alth o u g h hema­
t i t e i s fe rro m a g n e tic , th e d iffe re n c e s in s u s c e p t i b i l i t y f o r sm all
in c re a s e s in m a g n etizatio n a r e so sm all th a t h em atite could e a s ily be
m istak en f o r a param agnetic.
Small as i t i s , th e e x iste n c e o f rema­
nence i s in d is p u ta b le p ro o f o f th e ferro m ag n etic n a tu re o f h e m a tite .
54
The e f f e c t of tim e on th e remanence v alu es was not s tu d ie d
beyond a few q u a lita tiv e t e s t s which showed t h a t th e b lo ck s of hema­
t i t e s t i l l r e ta in e d a b o u t 90 p e rc e n t o f t h e i r remanent magnetism a f t e r
two m onths' time*
C oercive f o r c e *
The v a lu es of c o e rc iv e fo rc e found a re th e h ig h ­
e s t known in any n a tu r a l m in e ra l and, i n f a c t , th e h ig h e r valu e o f
2 ,4 0 0 o e rs te d s i s o f th e same o rd e r a s found o n ly in th e v e ry b e s t o f
th e r e c e n tly d isco v e re d permanent m agnets.
The v a r ia tio n o f c o e rc iv e fo rc e w ith s iz e of p a r t i c l e s in
powders cannot be ex p lain ed s a t i s f a c t o r i l y by th e p re s e n t th e o rie s o f
m agnetism.
Table XVI shows t h a t f o r Cumberland h em atite th e re i s a
change o f c o e rc iv e fo rc e w ith g ra in s iz e and th e r e s u l t s a re p lo tte d
i n f ig u r e 10*
This curve shows th a t th e c o erciv e fo rc e slow ly in c re a s e s
w ith in c re a s in g s u rfa c e u n t i l a g ra in s iz e of approxim ately 50 m icrons
i s reached*
There i s th e n a ra p id in c re a s e i n Hc f o r a sm all in c re a s e
i n a re a and a f t e r t h a t a grad u al in c re a s e as th e g ra in s iz e becomes
extrem ely sm all.
Because of th e sm all amount of re s e a rc h done on m in eral p h y sics
o u r knowledge of th e m agnetic p ro p e rtie s o f m in erals i s r a th e r meager
and o f f e r s l i t t l e o p p o rtu n ity f o r comparison o r c o r r e la tio n o f such
phenomena.
G o ttsch alk
49
has shown t h a t th e re i s a s t r a i g h t - l i n e r e l a t i o n ­
s h ip between Hc and g ra in s iz e f o r m agnetite and t h i s p r in c ip le has been
u sed in re s e a rc h f o r d e term in a tio n o f su rfa c e produced by g rin d in g .-50
^
See fo o tn o te 25d.
-50 F red DeVaney and W ill H. C o g h ill. Use o f th e C oercim eter in
G rinding T e s ts . A.I.M.M.E. Tech. Paper 862, 1938.
55
T here i s
n o s u c h l i n e a r r e l a t i o n s h i p f o r C um berland h e m a t i t e .
One
p o in t of i n t e r e s t i s th a t th e g r e a te s t change o f H ta k e s p la c e a t about
c
51
50 m icrons, which i s th e same s iz e a t which C h ev alier
n o tic e d th e
g r e a te s t change in s u s c e p t i b i l i t y w ith g ra in s iz e .
In th e lim ite d
number of t e s t s made on o th e r h e m a tite s , M ichigan no. 2 in d ic a te s th e
same tr e n d a s Cumberland h e m a tite , as shown in ta b le XVI, b u t i t was
n o t s iz e d f in e enough t o f in d o u t th e exact r e la tio n s h ip .
The C.P.
f e r r i c oxide has a h ig h He, as one m ight expect sin c e th e g ra in s iz e
i s o f alm ost m o lecu lar dim ensions.
The s u rp ris in g p a r t o f t h i s work
i s t h a t M ichigan h e m atite no. 1 showed no in d ic a tio n o f change in co­
e rc iv e fo rc e over a g ra in s iz e range from 0-5 m icrons to p ie c e s of ore
3 /8 ” sq u a re .
The q u e stio n n a tu r a lly a r is e s th e n as to what c o n s titu te s
•'magnetic s u rfa c e ” .
I t would appear th a t th e r e i s some lim itin g c r y s ta l
s iz e o f m in e ra l t h a t i s a s s o c ia te d w ith normal m agnetic p r o p e r tie s .
"When th e c r y s t a l i s reduced to a powder, new su rfa c e i s exposed w ith
a change of m agnetic p r o p e r tie s .
This might be lik e n e d to su rfa c e te n ­
s io n in liq u id s which i s caused by an unbalancing of fo rc e s a t th e su r­
fa c e o f th e l i q u i d .
I f th e liq u id i s sp read over a la r g e r a re a , th e
f r e e energy in th e system i s in c re a se d and a la r g e r fo rc e a c ts over th e
t o t a l s u rfa c e .
In m in erals th e in c re a s e in f r e e energy (cru sh in g and
g rin d in g ) produces new s u rfa c e down to some u n it m agnetic c r y s t a l .
Tdien
t h i s c r y s t a l i s broken in to powder form , th e su rfa ce te n s io n o r co erciv e
fo rc e in c re a s e s because more f r e e energy lias been added to th e system
to make up f o r th e unbalancing o f m agnetic moments a t th e s u rfa c e .
51
See fo o tn o te 4-7.
The
56
rem anent magnetism i s more t i g h t l y h e ld , and th e re fo re re q u ire s a
g r e a te r c o e rc iv e fo rc e to reduce i t to z ero .
This th e o ry would in d i­
c a te th a t th e u n it m agnetic c r y s t a l i n M ichigan h em atite no. 1 must
be le s s th a n 1 m icron and t h a t th e specimen i s extrem ely p o ly c ry s ta l­
lin e .
Time d id n o t allo w an X -ray exam ination of th e se h em atites to
a s c e r ta in d if f e r e n c e in c r y s t a l s tr u c tu r e b u t some such r e la tio n s h ip
p ro b ab ly e x is t s because th e r e i s a p a r a l l e l case in th e m anufacture of
permanent m agnets.
The m agnetic m a te ria ls a re mixed f o r th e magnets
and th e n given a p ro p e r h e a t tre a tm e n t to produce a magnet w ith c e r ta in
rem anence-coercive fo rc e c h a r a c t e r i s t i c s .
This h e a t tre a tm e n t i s prob­
a b ly a d is p e r s io n o f c e r ta in m a te ria ls i n th e a llo y to v ary th e "mag­
n e t i c s u rfa c e " .
Curve b in fig u r e 9 re p re s e n ts an attem p t to f in d th e Hc o f
h e m a tite a t s a tu r a tio n by means o f E e n n e lly ’s law .
This law i s a r e ­
statem e n t o f F r o h lic h 1s r e la tio n s h ip , which says t h a t "th e p e rm e a b ility
i s p ro p o r tio n a l to th e m a g n e tiz a b ility ” .
^max = a + b
Hc
O bviously th e r e s u lts shown in f ig u r e 9 do n o t f i t
any s t r a i g h t l i n e over th e e n tir e ra n g e .
t h a t h e m atite
I t fo llo w s from t h i s law th a t
i s n e ar s a tu r a tio n in f i e l d s
to makeu se o f a
Q u a lita tiv e ly th e y in d ic a te
o f 10,000 o e rs te d s .
Attem pts
s im ila r r e la tio n s h ip between Br and Bmax meet w ith even
le s s success*
The
H
v s . H curve shows th a t
max
o
in th e case o f t h i s h em atite
th e r e i s a l i n e a r r e la tio n s h ip between th e m agnetizing and dem agnetizing
__
—
E. L. Sanford and "VST. L. Chaney. The V a ria tio n o f R esid u al In ­
d u c tio n and C oercive Force w ith M agnetizing F orce. S c ie n t if ic Paper of
Bureau o f Standards no. 3&+, 1920.
57
f o r c e up to maximum s u s c e p t i b i l i t y a t about 3*500 o e rs te d s .
P ast
t h i s p o in t of maximum s u s c e p t i b i l i t y th e Hv drops r a p id ly w ith i n c re a s in g H ^ y
The curve shows t h a t a t t h i s p la c e th e r e e x is ts th e
maximum i n t e n s i t y o f m agnetization*
P a s t t h i s p o in t i t i s much more
d i f f i c u l t to tu r n th e magnetons a few more degrees f o r a b so lu te l i n ­
in g up w ith th e a p p lie d f ie ld *
Whereas i t may ta k e s e v e ra l thousand
o e rs te d s p a s t 1 ^ .^ to l i n e up th e m agnetons, th e a d d itio n a l Hc i s
sm all because of th e sm all amount o f tu rn in g done by th e magnetons.
The la r g e H v a lu e s show th a t commercial dem agnetization would be extre m e ly d i f f i c u l t .
I n f a c t , t h i s m a te ria l could n o t even be demagne­
t i z e d i n t h e la b o r a to r y .
i f th e HoC were known.
T h e o re tic a lly i t could have been demagnetized
P r a c tic a l ly , t h i s was alm ost im p o ssib le.
Thermomagnetic measurem ents.
The thermomagnetic curve shown in
f ig u r e 12 f o r h e m atite has been determ ined fr e q u e n tly ; th e curve has
53
th e same g e n e ra l form as th e one given by Rogers and Stamm.
The
param agnetic v alu e f o r s u s c e p t i b i l i t y above th e C urie p o in t, which i s
c a lle d th e param agnetic s u s c e p t i b i l i t y , was found to be 22 x 10"°, a
l i t t l e h ig h e r th a n th e average v alu e of 20 x 10
-6
given by C h ev alier
c/
and Begui;
e r r o r s in zero c o rre c tio n on th e balan ce would probably
account f o r t h i s d if f e r e n c e .
The C urie p o in t o f about 685° C. i s in
accord w ith th e accep ted valu e fo r Fe 20 3 .
53
See fo o tn o te 16.
54- Raymond C h ev alier and Z. Esm ail Begui. Thermomagnetic Prop­
e r t i e s of F e r r ic Oxide. Soc. Chimique, November 1937, pp. 1735-4-1.
58
A h y s te r e s is loop was ru n on th e m a te ria l b efo re h e at t r e a t ­
ment and th e r e s u l t s a re shown i n th e sm a lle r loop o f fig u r e 1 3 .
The shape o f th e h y s te r e s is curve shows t h a t th e method de­
veloped in t h i s in v e s tig a tio n i s v a lid f o r both ty p e s o f m agnetic
b a la n c e s.
The m a te ria l was th en h e a te d to i t s C urie p o in t o f 685 °
and cooled in a m agnetic f i e l d o f about 7,000 o e rs te d s .
A h y s te r e s is
loop was th e n ru n once more and i t was found t h a t both th e remanence
and c o e rc iv e fo rc e had in c re a s e d , as shown by th e o u te r h y s te r e s is
lo o p .
The i n t e r p r e t a t i o n o f an in c re a s e in both Br and Hc i s d i f f i ­
c u lt.
K o e n ig sb e rg e r^ has re p o rte d th a t m agnetite a cq u ired a remanence
100 to 1,000 tim es g r e a te r th a n th e normal Br when cooled from i t s C urie
p o in t i n a m agnetic f i e l d .
Bozorth and D illin g e r
h e a t- tr e a te d perma­
n e n t magnet m a te ria ls i n a m agnetic f i e l d and in some cases found an
enormous in c re a s e in p e rm e a b ility b u t a lo s s in co erciv e f o r c e , a l l o f
which th e y a ttem p ted to e x p la in on th e b a s is o f th e domain th e o ry .
It
i s conceivable th a t th e axes o f a l l th e elem entary magnetons become
p a r a l l e l i n a m agnetic f i e l d when h e ate d , because as th e th erm al a g ita ­
t i o n in c re a s e s i t becomes e a s ie r to tu rn th e elem entary magnet i n th e
d ir e c tio n o f th e f i e l d .
A t, say, 1° under th e C urie p o in t, th e re i s
55 J . G. K oenigsberger. S ta b i l i t E t d er m agnetischen Thermoremanenz
in Tongegenstanden und G esteinen b e i Bestimmungen des M agnetischen
E rd fe ld es in d e r V ergangheit. G erlands B eitra g e Zur Geophysik, 5A,
Book 1 , 1938.
5^ R. M. B ozorth and J . F. D illin g e r . Heat Treatment of Magnetic
M a te ria ls in a M agnetic F ie ld . P h y sic s, 6, 1935, pp. 279-85.
59
s a tu r a tio n -when only an extrem ely sm all f i e l d i s u sed .
As th e temper­
a tu r e d e c re a se s, th e magnets s t i l l te n d to s ta y p a r a l l e l -with th e f i e l d
and th e r e i s s a tu r a tio n a t low er te m p e ra tu re s.
I t i s h a rd e r to e v a l­
u a te th e domain c o n trib u tio n to such an in c re a s e in magnetism.
The
v e ry n a tu re of th e domain th e o ry would demand t h a t tremendous f i e l d s
be used d u rin g c o o lin g i f th e domains a re to be k ep t in alignm ent.
In th e case of th e h e m atites t e s t e d , both Bp and Hc in c re a se d
s lig h tly .
Br
Had th e r e been a conversion to m agnetite during h e a tin g
would have in c re a s e d b u t He would have decreased due to i t s low
v a lu e i n com parison w ith hem atite*
I t appears th e re fo re t h a t th e in ­
flu e n c e o f c o o lin g in a m agnetic f i e l d i s r e a l , and su g g ests th a t an
e x p la n a tio n in term s of thermodynamic th e o ry should be p o s s ib le .
No
such e x p la n a tio n f o r th e e x tr a energy o f th e in c re a s e d a re a o f th e hys­
t e r e s i s drop has been given, to our knowledge.
This m atter lias p r a c ti c a l
as w e ll as t h e o r e t i c a l i n t e r e s t and m e rits f u r th e r c o n s id e ra tio n .
A p p lic a tio n to m agnetic s e p a ra tio n .
D i f f i c u l t i e s encountered in
developing th e ex p erim en tal method consumed so much tim e t h a t l i t t l e
was done on th e a p p lic a tio n o f th e d a ta o b ta in in g on m agnetic sep ara­
tio n .
Q u a lita tiv e t e s t s were made
by
suspending a paper b earin g th e
m agnetized h e m atite over a sm all a lte r n a t in g c u rre n t f i e l d .
The jump­
in g a c tio n due to re p u ls io n was so f a i n t in a l l t r i a l s t h a t no concen­
t r a t i o n o f h e m atite was p o s s ib le .
A f u r th e r study of th e e f f e c t o f
change i n f i e l d a lte r n a t io n might be a d v isa b le sin c e only 60 cy cle cu r­
r e n t was used in th e s e experim ents.
The tremendous co erciv e fo rc e of
h e m a tite m agnetized in high f i e l d s would allow th e use o f la rg e a l t e r ­
n a tin g c u rre n t s e p a ra to rs and perhaps th e fo rc e o f re p u ls io n could be
e a s e s
60
in c re a s e d i n t h i s manner.
These t e s t s le a d to th e same f a c t —a m in eral
must have a f a i r l y h ig h c o e rc iv e fo rc e and remanence to be amenable to
a lte r n a t in g c u rre n t m agnetic s e p a ra tio n .
w ith a la r g e remanence but such a low
On one hand we have m ag n etite
c o erciv e fo rc e t h a t an a l t e r n a t ­
in g f i e l d of any consequence dem agnetizes i t a t each a lte r n a t io n , o r
r a t h e r , th e m a te r ia l i s so m a g n e tic a lly s o f t t h a t th e p o le s change w ith
each a lt e r n a t i o n and th e r e i s no rep u lsio n *
At th e o th e r extreme i s
h e m a tite w hich has a c o erciv e fo rc e capable of w ith sta n d in g la rg e a l t e r ­
n a tin g f i e l d s but w ith so l i t t l e remanence th a t th e fo rc e of re p u ls io n
i s to o sm all to move th e h e m atite p a r t i c l e s and hence to be used in
a lte r n a t in g c u rre n t m agnetic s e p a ra tio n a t th e p re s e n t tim e .
Heat tre a tm e n t to a l t e r th e remanence and c o erciv e fo rc e
o f f e r s in t e r e s t i n g p o s s i b i l i t i e s .
I t might be p o s s ib le to s a c r i f i c e
p a r t of th e Hc f o r a gain in remanence, such as i s done in th e case
o f permanent m agnets.
H eating to th e C urie p o in t (680° C .) and cooling
i n a m agnetic f i e l d m ight h e lp to in c re a s e th e remanence but th e eco­
nomics of t h i s h e a t tre a tm e n t would have to be compared w ith th e p re s e n t
red u cin g r o a s t p ro c e ss .
61
CONCLUSIONS
1*
The u se of th e Gouy-type m agnetic balan ce has been ex­
ten d ed so t h a t i t i s p o s s ib le to measure th e h y s te r e tic c o n sta n ts of
w eakly fe rro m ag n e tic m a te r ia ls ,
2.
Alpha h e m atite has been shown to be d i s t i n c t l y f e r r o ­
m agnetic because:
a.
I t s Xg v s , H curve shows a maximum,
b.
I t e x h ib its r e s id u a l magnetism*
c*
A d e f in ite c o erciv e fo rc e i s re q u ire d to reduce i t s
rem anent magnetism to z e ro .
d*
3*
I t has a C urie p o in t.
The h y s te r e s is phenomena can be a tt r i b u t e d on ly to hema­
t i t e , and n o t to o th e r ferro m ag n etic im p u r itie s , because of th e la rg e
c o e rc iv e fo rc e v a lu e s and because of th e maximum X t h a t occurs a t
g
h ig h f i e l d s .
4.
H em atite approaches s a tu r a tio n in f i e l d s o f 10,000 o e rs te d s .
5.
The s li g h t re p u ls io n o f h em atite from an a lte r n a t in g c u rre n t
f i e l d a f t e r m a g n etiza tio n in h ig h d ir e c t c u rre n t f i e l d s i s i n s u f f ic ie n t
f o r p r a c t i c a l c o n c e n tra tio n by such means.
The remanence i s so low and
th e h e m atite i s so n e a r s a tu r a tio n in f i e l d s of 10,000 o e rs te d s th a t
" a c tiv a tin g 11 th e h e m a tite in f i e l d s o f 25*000 to 30,000 o e rste d s would
n o t h e lp v e ry much.
6.
The f a c t t h a t h e m atite i s ferro m ag n etic even though th e
s u s c e p t i b i l i t y v a lu es a re on ly th o se o f a s tro n g ly param agnetic substance
su g g ests a d e f in itio n o f ferrom agnetism based on h y s te r e tic phenomena.
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