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Mat.-wiss. u. Werkstofftech. 2013, 44, No. 2–3
DOI 10.1002/mawe.201300092
Magnetoresistance of multi-walled carbon nanotubes
modified with iron
Der magnetoresistive Effekt von mit Eisen modifizierten mehrschaligen
Kohlenstoffnanoröhren
I. V. Ovsienko1, L.Y. Matzui1, I. V. Yatsenko1, S. V. Khrapatiy1, Y. I. Prylutskyy1, U. Ritter2, P. Scharff2,
F. Le Normand3
The dependence of the magnetoresistance of iron-doped multi-walled carbon nanotubes (FeMWCNTs) on the carbon nanotubes arrangement, the temperature, the relative orientation of
the magnetic field, and the current was investigated. The findings show that the magnetoresistance of partially-oriented Fe-MWCNTs is due to a combination of two mechanisms: (1) the giant
magnetoresistance (GMR) that takes place in layered or cluster systems consisting of magnetic
and nonmagnetic materials, and (2) the anisotropic magnetoresistance which is characteristic
of ferromagnetic metals. For array-oriented Fe-MWCNTs the dominant mechanism of magnetoresistance depends on the relative orientation of the magnetic field and current through the
sample, namely it depends on the localization mechanism at the mutually perpendicular orientation of the magnetic field and current and the GMR effect in mutual parallel orientation of
the magnetic field and current.
Keywords: Multi-walled carbon nanotubes / giant magnetoresistance / anisotropic magnetoresistance /
Der magnetoresistive Effekt von mehrschaligen mit Eisen gefüllten Kohlenstoffnanoröhren (FeMWCNTs) wurde untersucht. Dabei wurde der Magnetwiderstand in Abhängigkeit von der Struktur der Kohlenstoffnanoröhren, der Messtemperatur und der relativen Orientierung des Magnetfeldes und -stroms untersucht. Für nur wenig orientierte Fe-MWCNTs konnte gezeigt werden,
dass der beobachtete Magnetwiderstand durch die Kombination von zwei unterschiedlichen
Mechanismen entsteht: (1) der Riesenmagnetwiderstand (GMR), welcher in Schicht- oder Clustersystemen aus magnetischen und nichtmagnetischen Materialien entsteht, (2) der anisotrope
Magnetwiderstand, welcher charakteristisch für ferromagnetische Materialien ist. Für ausgerichtete Fe-MWCNTs ist der bestimmende Mechanismus abhängig von der relativen Orientierung
des Magnetfeldes und -stroms durch die Probe, insbesondere vom Lokalisierungsmechanismus
bei der senkrechten Orientierung des Magnetfeldes und -stroms und beim GMR Effekt von der
parallelen Orientierung des Magnetfeldes und -stroms.
Schlüsselwörter: mehrschalige Kohlenstoffnanoröhren / Riesenmagnetwiderstand / anisotroper Magnetwiderstand /
1 Introduction
Due to considerable progress in the development of spintronics,
the efforts of researchers are currently focused on magnetic
nanostructures made of different types, which have combined
magnetic and nonmagnetic phases. It is related with the fundamental problems of the nature of magnetism in nanostructures
1
Taras Shevchenko National Univesity of Kyiv, Kyiv, Ukraine
Ilmenau University of Technology, Department of Chemistry, Ilmenau,
Germany
3
institut de Physique et Chimie des Mat�riaux, Strasbourg, France
2
Corresponding author: I.V. Ovsienko, Taras Shevchenko National University of Kyiv, Volodymyrska Str. 64, 01601 Kyiv, Ukraine
E-mail: ovsienko@mail.univ.kiev.ua
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2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
and their considerable applied potential. In this regard, the considerable attention is paid to the study of magnetic systems based
on carbon materials of different dimensions, which can be magnetic memory elements, magnetic sensors and others. So, the
considerable interest is study of graphite intercalated magnetic
metals in which the non-magnetic graphite layers alternate with
layers of magnetic metal [1 – 2]. According to the data of theoretical simulation, the properties of charge carriers are changed significantly, in particular, the degree of electron’s polarization
could reach even 100% due to the interaction between graphite
layers enriched by the additional charge carriers with the layers
of metal [3 – 4]. Another promising for spintronics material is carbon nanotubes (CNTs), which is considered as future molecular
devices and elements of nanoelectronics [5 – 6]. Obviously, that
CNT modification by magnetic metals, particular the introduc-
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I. V. Ovsienko et al.
Mat.-wiss. u. Werkstofftech. 2013, 44, No. 2–3
Figure 1. HRTEM image of first type MWCNT's specimen (outer
diameter is 63 nm, and inner diameter 8 nm).
Bild 1. HRTEM-Abbildung von MWCNTs des ersten Typs (AuГџendurchmesser 63 nm und Innendurchmesser 8 nm).
tion of magnetic metal particles in the inner cavity of the CNT,
deposition of magnetic metal particles on the CNT surface and
between layers of multi-walled CNT (MWCNTs) alter not only
their electronic structure, but also lead to changes in magnetic
properties of the modified CNTs [7 – 8]. Also, a significant number of works devoted to magneto-transport research in singlewalled CNTs (SWCNTs) and MWCNTs, which have a contact
with ferromagnetic electrodes [9 – 10]. These CNTs are perfect
spin-transport medium as their electron transport is one dimensional and ballistic with expectedlong spin relaxation length as
well as negligible spin orbit effects.
This paper presents experimental results on magnetoresistance in MWCNTs, which include internal cavity of the particle
magnetic phases, depending on temperature, the relative orientation of the magnetic field and current and ordering samples.
2 Experimental
We have used two different types of MWCNTs for our studies.
The first type of MWCNTs was produced by means of chemical
vapor deposition technique in tube furnace using benzene as carbon source material and ferrocene as iron source material and
catalyst. Fig. 1 presents typical TEM image of these MWCNTs.
Evidently, the CNTs produced by this method are multi-walled
with the external and inner tube diameters in the ranges 60 – 70
nm and 6 – 15 nm, respectively. These MWCNT contain iron clusters (or iron compounds) with average diameter (10 – 15) nm and
length (120 – 140) nm. According to X-ray diffraction analysis the
graphite structures with interplanar distance d002 = 0.341 nm,
corresponding to fine crystal graphite, are identified in this sam-
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2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Figure 2. TEM images of second type MWCNT's specimen: (a) and (b)
are different magnification (outer diameter is 75 nm, and inner diameter 5 – 8 nm).
Bild 2. TEM-Abbildungen von MWCNTs des zweiten Typs: (a) und (b)
unterschiedliche Auflösungen (Außendurchmesser 75 nm und Innendurchmesser 5 – 8 nm).
ple [11]. Phases of a-iron, oxide of iron (III) and iron carbide
(cementite) present in the sample too.
A sample of different type represents an array of parallel oriented MWCNTs, in the inner cavity of which are particles of iron
or its compounds with a diameter of ~(5 – 10) nm, Fig. 2. Note
that the atomic planes are not oriented parallel with the axis of
the nanotube, but they display a definite angle with it. According
to X-ray diffraction analysis a-iron and oxide of iron (III) particles
are presence in the inner cavity of MWCNT [12].
For magnetoresistance investigations bulk specimens from
MWCNT's of first type powder have been prepared by cold compacting without binder [13]. The size of bulk specimens is
(156361) mm. Note that the axis of individual MWCNTs, oriented arbitrarily, located mainly in the plane of the sample. With
the array of MWCNT's (specimen of second type) were cut the
samples with a size of (86361) mm.
Measurement of electrical resistance was carried out by standard four-probe method with direct current [13]. Electrical resistiv-
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Mat.-wiss. u. Werkstofftech. 2013, 44, No. 2–3
Magnetoresistance of multi-walled carbon nanotubes modified with iron
Figure 3. q = f (T) dependence for first type MWCNT's specimen (a): 1:
experimental and 2: calculated values (assuming only classical scattering mechanisms); Dr = f (ln T) dependence (b).
Bild 3. q = f (T)-Abhängigkeit für MWCNTs des ersten Typs (a): 1:
Experiment und 2: berechnet (angenommen wurde ein klassischer
Streumechanismus); Dr = f (ln T) Abhängigkeit (b).
ity was measured in a magnetic field to 1.5 T at 293 and 77 K for
two orientations of the magnetic field relative to current through
the sample. For the first type MWCNT's specimen the magnetic
field was directed perpendicular and parallel to the current
through the sample. The temperature dependence of electrical
resistivity in the temperature range from 4.2 to 293 K was also
measured for this sample. For the second type MWCNT's specimen the resistivity was measured perpendicular to the axis of the
MWCNT. Magnetoresistance measurement for this sample was
conducted in two configurations: a magnetic field perpendicular
and parallel to the current through the sample. Magnetoresistance is defined as:
ГЃR
RB ГЂ R0
Вј
R0
R
where RB is specimen's resistance in magnetic field and R0 –
without magnetic field.
3 Results and discussion
Fig. 3a shows the temperature dependence of resistance along
the plane of first type MWCNT's specimen. It can be seen that
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2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Figure 4. DR/R(B) dependence for first type MWCNT's specimen: (a) B
? I and (b) B || I; T = 293 K.
Bild 4. DR/R (B)-Abhängigkeit für MWCNTs des ersten Typs: (a) B ? I
and (b) B || I; T=293 K.
the resistance decreases with temperature and such behavior is
typical for fine crystal carbon materials, in which the predominant mechanism of scattering of charge carriers is scattering at
the boundaries of crystallites, which is temperature independent
[14]. The ratio of q 77/q 293 is 1.33. At a temperature less than 77
K a sharp increase in electrical resistance is observed, that can be
explained by means of the theory of quantum effects of weak
localization and electron-electron interaction of charge carriers,
manifested in systems with weak disordering. According to the
theory [15-17], an amendment to the conduction Dr can be represented as Dr ~ lnT due to the action of the above quantum effects
in two-dimensional case. Fig. 3b demonstrates the linear dependence Dr = f (lnT), where Dr (T) = r exp (T) – Drp (T) (DrP (T) is
the electrical conductivity of the sample considering only classical scattering mechanisms.
Fig. 4 presents the dependences of lateral (a) and longitudinal
(b) magnetoresistance on the magnetic field at the room temperature. Apparently, there is a hysteresis phenomenon. To configure of lateral magnetoresistance the resistance increases with
increasing magnetic field to a value of 0.8 T and then decreases
sharply and tends to be negative. At the parallel orientation of the
magnetic field and current in the sample the weakly pronounced
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I. V. Ovsienko et al.
Figure 5. DR/R (B) dependence for first type MWCNT's specimen: (a) B
? I and (b) B || I; T = 77 K.
Bild 5. DR/R(B)-Abhängigkeit für MWCNTs des ersten Typs: (a) B ? I
und (b) B || I; T = 77 K.
local maximum of magnetoresistance is observed at 0.6 T. In
both cases the field saturation is not achieved. Change the value
of magnetoresistance in the case of perpendicular orientation of
current and magnetic field is ~2.3%, and in case of parallel orientation of current and field – ~4.0%.
The possible causes of such complex magnetoresistance
dependence for this type of sample are as follows: It is known
that in layered or clustered systems with alternating magnetic
and nonmagnetic layers or magnetic clusters are in a nonmagnetic matrix, the phenomenon of giant magnetoresistance
(GMR) is observed. Its reason is the spin-orbit interaction of
charge carriers leading to spin-dependent scattering of electrons.
In the initial state (at zero magnetic field) the magnetic moments
of magnetic metal particles are oriented randomly. In this case,
the resistance system is a maximum due to the scattering of
charge carriers on the spin magnetic particles of the metal atoms.
When the external field orients the magnetic moments of magnetic metal particles in parallel, the scattering of charge carriers
and, thus, the electrical resistance decrease. A characteristic feature of GMR is a hysteresis phenomenon in the case of magnetoresistance dependence on magnetic field.
Another possible mechanism for magnetoresistance in systems containing magnetic metals in nonmagnetic matrix is ani-
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2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Mat.-wiss. u. Werkstofftech. 2013, 44, No. 2–3
Figure 6. DR/R(B) dependence for second type MWCNT's specimen: (a)
T = 293 K and (b) T = 77 K; B ? I.
Bild 6. DR/R(B)-Abhängigkeit für MWCNTs des zweiten Typs: (a) T =
293 K und (b) T = 77 K; B ? I.
sotropic magnetoresistance (AMR). For ferromagnetic materials
the electrical resistance in a magnetic field depends on the angle
h between the direction of magnetization (M) and an external
magnetic field (B). A characteristic feature of AMR is a dependent of sign magnetoresistance on the relative orientation of the
magnetic field M and current I
RГ°M;I Гћ Вј R0 Гѕ RГЃ ГЃ cos2 Г°M;I Гћ
where RD R || – R? [18].
The magnetoresistance of sample has both positive and negative values, Fig. 4. Moreover, the changing character of magnetoresistance dependence on the magnetic field in both configurations is at (0.6 – 0.8) T. This behavior is characteristic magnetoresistance if the orientation of the axis of easy magnetization does
not coincide with the direction of current flow. First, with
increasing the field to the value of (0.6 – 0.8) the magnetization of
iron particles along the axis of easy magnetization, which is oriented, obviously, at a certain angle to the direction of current,
takes place. Upon reaching value of (0.6 – 0.8) T, a remagnetization of iron particles along the direction of the external field
occurs.
Similar in form, but less pronounced in magnitude the magnetoresistance dependences in this sample at two different orien-
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Mat.-wiss. u. Werkstofftech. 2013, 44, No. 2–3
Magnetoresistance of multi-walled carbon nanotubes modified with iron
effect. The hysteresis phenomenon is observed. At maximum
value of the magnetic field the magnetoresistance saturates, but
the effect is small – ~0.5%. With decreasing temperature of the
sample to 77 K the hysteresis phenomena and saturation of magnetoresistance disappear (effect decreases to 0.4%), that directly
points to display in this sample of GMR effect due to the spinpolarized scattering charge. At room temperature the spin polarization occurs at small values of the magnetic field, that leads to a
decrease in spin-polarized scattering of charge carriers in a magnetic field and, thus, to an increase of conductivity of the sample.
With decreasing temperature there is a “frozen” spin-orbit scattering and the spin polarization can be achieved only at large values of the magnetic field.
4 Conclusions
Studies of magnetoresistance of iron-doped MWCNTs demonstrate that their resistance in magnetic field strongly depends on
their structure and mutual orientation, as well as on structural
and morphological state of magnetic phase. For partially oriented
Fe-MWCNT's the magnetoresistance is determined by a combination of two mechanisms, namely, GMR and AMR. For arrayoriented Fe-MWCNT's in mutually perpendicular orientation of
the magnetic field and current a principal mechanism is the
localization magnetoresistance mechanism, and in mutual parallel orientation of the magnetic field and current – a GMR
effect.
Figure 7. DR/R(B) dependence for second type MWCNT's specimen: (a)
T = 293 K and (b) T=77 K; B || I.
Bild 7. DR/R(B)-Abhängigkeit für MWCNTs des zweiten Typs: (a) T =
293 K und (b) T = 77 K; B || I.
tations of the magnetic field and current are observed in the field
dependence of magnetoresistance at 77 K, Fig. 5. In this case the
field, in which the changing magnetization direction is observed,
is ~1 T.
Fig. 6 shows the field dependences of magnetoresistance of
array-oriented Fe-MWCNTs for following configuration: the
magnetic field perpendicular to the current through the sample
at two temperatures 293 and 77 K. The magnetoresistance is negative and the magnitude of the effect increases from 0.1% at
room temperature to 0.4% at 77 K. The phenomenon of hysteresis in the case of magnetoresistance dependence on the magnetic
field is not observed and magnetoresistance is quadratic for the
field. Authors [19] observed the similar dependences of transverse magnetoresistance from the magnetic fields for CNT films
in the temperature range from 1.7 to 180 K. Obviously, in this
case, the principal mechanism of magnetoresistance is the localization mechanism associated with the breakdown of weak localization of charge carriers in a magnetic field and the presence of
magnetic impurities.
Fig. 7 presents the field dependence of magnetoresistance for
array-oriented Fe-MWCNTs in the case of magnetic field parallel
current at 293 and 77 K. The behavior of the field dependence of
magnetoresistance at 293 K is a typical for the case of the GMR
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2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Acknowledgments
This work was partly supported by the STCU (grant N4908),
NATO (project N UKR.SFPP 984243) and by the Deutsche Forschungsgemeinschaft (DFG).
5 References
[1] D. V. Matsui, Y. I. Prylutskyy, L. Y. Matzuy, F. Le Normand,
U. Ritter, P. Scharff, Physica E 2008, 40, 2630.
[2] D. Matsui, Y. Prylutskyy, L. Matzui, M. Zakharenko, F. Le
Normand, A. Derory, Phys. St. Sol. C 2010, 7, 1264.
[3] B. Solange, Fagan, R. Mota, Antionio J. R. da Silva, A. Fazzio, Physica B 2003, 340, 982.
[4] V. V. Ivanovskaya, C. Köhler, G. Seifert, Phys. Rev. B 2007,
75, 075410.
[5] G. C. McIntosh, G. T. Kim, J. G. Park, V. Krstic, M. Burghard, S. H. Jhang, S. W. Lee, S. Roth, Y. W. Park, Thin Sol.
Films 2002, 417, 67.
[6] A. Cottet, T. Kontos, S. Sahoo, H. T. Man, M. S. Choi, W. Belzig, C. Bruder, A. F. Morpurgo, C. Schonenberger, Semicond. Sci. Technol. 2006, 21, 78.
[7] N. Grobert, W. K. Hsu, Y. Q. Zhu, J. P. Hare, H. W. Kroto,
D. R. M. Walton, M. Terrones, H. Terrones, P. Redlich, M.
Ruehle, R. Escudero, F. Morales, Appl. Phys. Lett. 1999, 75,
3363.
[8] K. Tsukagoshi, B. W. Alphenaar, Superlat. Microstruct. 2000,
27, No. 5/6.
www.wiley-vch.de/home/muw
165
166
I. V. Ovsienko et al.
[9] A. Jensen, J.R. Hauptmann, J. NygГҐrd, P.E. Lindelof, Phys.
Rev. B 2005, 72, 035419.
[10] N. Kang, J. S. Hu, W. J. Kong, L. Lu, D. L. Zhang, Z. W. Pan,
S. S. Xie, Phys. Rev. B 2002, 66, 241403.
[11] G. E. Grechnev, V. A. Desnenko, A. V. Fedorchenko, A. S.
Panfilov, L. Y. Matzui, Y. I. Prylutskyy, Y. V. Goncharenko,
U. Ritter, P. Scharff, Y. A. Kolesnichenko, Low Temp. Phys.
2010, 36, 1086.
[12] F. Le Normand, C. T. Fleaca, M. Gulas, A. Senger, O. Ersen,
I. N. Mihailescu, G. Socol, D. Muller, M. C. Marco De Lucas,
J. Mater. Res. 2008, 23, 619.
[13] L. Y. Matzui, I. V. Ovsienko, T. A. Len, Y. I. Prylutskyy, P.
Scharff, Fuller. Nanotubes Carbon Nanostruct. 2005, 13, 259.
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Mat.-wiss. u. Werkstofftech. 2013, 44, No. 2–3
[14] L. Y. Matzui, I. V. Ovsienko, L. Vovchenko, Low Temp. Phys.
2001, 27, 68 (in Russian).
[15] B. L. Altshuler, JETP 1978, 75, 1330 (in Russian).
[16] B. L. Altshuler, A. G. Aronov, Lett. JETP 1978, 27, 700 (in
Russian).
[17] B. L. Altshuler, A. G. Aronov, JETP 1979, 77, 2028 (in Russian).
[18] K. C. Christides, J. Appl. Phys. 2003, 94, 2516.
[19] G. Baumgartner, M. Carrard, L. Zuppiroli, W. Bacsa, Walt
A. de Heer, L. Forro, Phys. Rev. B. 1997, 55, 6704.
Received of final form: November 28th 2012
T 92
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