Anomalous magnetic behavior in nanocomposite materials of reduced graphene oxide-

Ni/NiFe2O4
Pratap Kollu, Sateesh Prathapani, Eswara K. Varaprasadarao, Chella Santosh, Sudhanshu Mallick, Andrews
Nirmala Grace, and D. Bahadur

Citation: Applied Physics Letters 105, 052412 (2014); doi: 10.1063/1.4892476

View online: http://dx.doi.org/10.1063/1.4892476
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/105/5?ver=pdfcov
Published by the AIP Publishing

Articles you may be interested in

Enhanced magnetic behavior, exchange bias effect, and dielectric property of BiFeO3 incorporated in
(BiFeO3)0.50 (Co0.4Zn0.4Cu0.2 Fe2O4)0.5 nanocomposite
AIP Advances 4, 037112 (2014); 10.1063/1.4869077

Role of inhomogeneous cation distribution in magnetic enhancement of nanosized Ni0.35Zn0.65Fe2O4: A

structural, magnetic, and hyperfine study
J. Appl. Phys. 114, 093901 (2013); 10.1063/1.4819809

Magnetic behavior of reduced graphene oxide/metal nanocomposites

J. Appl. Phys. 113, 17B525 (2013); 10.1063/1.4799150

Sol-gel NiFe2O4 nanoparticles: Effect of the silica coating

J. Appl. Phys. 111, 103911 (2012); 10.1063/1.4720079

Electrospinning and multiferroic properties of NiFe 2 O 4 – Pb ( Zr 0.52 Ti 0.48 ) O 3 composite nanofibers

J. Appl. Phys. 104, 024115 (2008); 10.1063/1.2959831

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 86.4.50.211
On: Sun, 10 Aug 2014 16:01:08
 APPLIED PHYSICS LETTERS 105, 052412 (2014)

Anomalous magnetic behavior in nanocomposite materials of reduced

graphene oxide-Ni/NiFe2O4
Pratap Kollu,1,a),b) Sateesh Prathapani,2 Eswara K. Varaprasadarao,2 Chella Santosh,3
Sudhanshu Mallick,2 Andrews Nirmala Grace,3,b) and D. Bahadur2,b)
1
DST-INSPIRE Faculty, Department of Metallurgical Engineering and Materials Science,
Indian Institute of Technology Bombay, Mumbai 400076, India
2
Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay,
Mumbai 400076, India
3
Centre for Nanotechnology Research, VIT University, Vellore 632014, India
(Received 2 May 2014; accepted 26 July 2014; published online 7 August 2014)
Magnetic Reduced Graphene Oxide-Nickel/NiFe2O4 (RGO-Ni/NF) nanocomposite has been
synthesized by one pot solvothermal method. Respective phase formations and their purities in the
composite are confirmed by High Resolution Transmission Electron Microscope and X Ray
Diffraction, respectively. For the RGO-Ni/NF composite material finite-size effects lead to the
anomalous magnetic behavior, which is corroborated in temperature and field dependent magnet-
ization curves. Here, we are reporting the behavior of higher magnetization values for Zero Field
Cooled condition to that of Field Cooled for the RGO-Ni/NF nanocomposite. Also, the observed
negative and positive moments in Hysteresis loops at relatively smaller applied fields (100 Oe and
C 2014 AIP Publishing LLC.
200 Oe) are explained on the basis of surface spin disorder. V
[http://dx.doi.org/10.1063/1.4892476]

Ever since the discovery of graphene,1 researchers have there will be a perturbation in graphene properties on addi-
been exploring its potential application in organic flexible tion of magnetic impurities.
electronics, transistors, and optoelectronic devices.2 On size reduction, magnetic properties of nanosized
Recently, magnetic tunnel junctions based on graphene are particles are dominated by finite-size effects because of com-
demonstrated for devices such as reprogrammable spin logic, petence between core and surface magnetic properties.
tunnel transistor, and non-volatile magnetic memory.3 Under-finite size effects, Kodama et al.13,15 have proposed
Composite material of Graphene-Fe3O4 magnetic paper is the surface spin disorder in NF nanoparticles. In ferrite nano-
developed for magnetic controlled switches as mechanical particles, intra-sublattice exchange is weaker than the inter
actuators.4 Tunable dielectric constant values from negative sublattice exchange leading to bulk ferrimagnetism and the
to positive and a higher magneto-resistance of 46%–72% to superexchange interactions between magnetic cations occur
that of pristine graphene is reported for the composite of through intermediary oxygen. When oxygen atom is released
Graphene-Fe/Fe3O4 by Zhu et al.5 Graphene usage is also from the surface of the nanoparticle then the exchange bond
explored in the form of magnetic composites with nickel fer- breaks thus broken bonds are created. In case of organic-
rite (NF) for applications; including as an anode material for ferrite composites, the broken exchange bonds are bonded
Li-ion batteries,6 microwave absorbing material,7 and for by organic species leading to the absence of superex-
photocatalysis in removal of organic dyes.8 change.16 Any type of these broken exchange bonds reduce
There are numerous studies on magnetic properties of the effective coordination of surface cations on the nanopar-
graphene9–11 and nano sized nickel ferrite individually,12,13 ticle surface causing surface spin disorder or canted surface
but studies related to their composite magnetic behavior are spin structures. These canted spin structures freeze into a
limited. Recently, quantum Monte Carlo simulations have spin-glass like phase around a temperature of 50 K for
shown an indirect coupling between magnetic impurities for NF.13,15 Keeping in mind the theories and models in antici-
a system comprising of magnetic nanoparticles decorated on pation of different kind of behavior, we have synthesized
the zigzag edge of graphene and have shown improved anti- nanocomposite materials of Reduced Graphene Oxide-
ferromagnetic correlations in it.9 Density Functional Theory Nickel/Nickel Ferrite (RGO-Ni/NF) nanocomposite and in
(DFT) calculations for transition metal adsorbed on graphene this report; we are presenting the anomalous behavior of
surface have shown the possibility of charge transfer from “temperature and field dependent magnetization” at low field
the adsorbed transition metal to graphene surface and signifi- (about 100 Oe and 200 Oe).
cantly changed its electronic density of states near the Fermi With the experience of extensive study on graphene17
region.14 The above theoretical calculations suggest that and graphene based magnetic composites,18 we have syn-
thesized RGO-Ni/NF nanocomposite by one pot solvother-
mal synthesis by dispersing the appropriate quantities of
a)
Present address: Newton International Fellow, Thin Film Magnetism Group, precursor materials in ethylene glycol. Precursor materials
Cavendish Laboratory, Department of Physics, JJ Thomson Avenue,
include FeCl36H2O, NiCl26H2O, and previously prepared
University of Cambridge, Cambridge CB3 0HE, United Kingdom.
b)
Authors to whom correspondence should be addressed. Electronic addresses: (modified Hummer’s method) GO. The dispersed precursors
pk419@cam.ac.uk, anirmalagrace@vit.ac.in, and dhirenb@iitb.ac.in are ultrasonicated for 2 h. Subsequently, sodium acetate and

0003-6951/2014/105(5)/052412/4/$30.00 105, 052412-1 C 2014 AIP Publishing LLC

V

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 86.4.50.211
On: Sun, 10 Aug 2014 16:01:08
 052412-2 Kollu et al. Appl. Phys. Lett. 105, 052412 (2014)

polyethylene glycol have been added in appropriate amount

with continuous stirring for 30 min. The mixture has been
transferred to a Teflon-lined stainless steel autoclave and
thermally heated at 200  C for 10 h. The resultant black
product has washed with MilliQ water and ethanol several
times by centrifugation and is dried at 45  C in vacuum
oven. Further, it was used for various characterizations.
Fig. 1 shows the X Ray Diffraction (XRD) micrograph
for RGO-Ni/NF nanocomposite with all peaks corresponding
to three phases. Peaks with symbol (D) indicate typical spi-
nel structure of NF with Fd3m space group,20 and peaks with
symbol ($) represent Nickel (Ni) nanoparticles that belong to
space group Fm3m.21 Presence of RGO is confirmed from
the peak (around 2h ¼ 23 marked with the symbol (*).20
Fig. 2(a) is a High Resolution Transmission Electron
Microscope (HRTEM) image of RGO-Ni/NF, which shows
the uniform distribution of magnetic phases over RGO.
Because of strong adsorption, the RGO layers are crumpled
(as shown in Figure 2(b)) around the magnetic nanoparticles
of (Ni/NF). This may lead to some structural disorder
associated with some strain at the surface of magnetic nano-
particles. Williamson-Hall plot (W-H plot) (b Cos h ¼ e
Sin h þ 0.9k/D) is used to estimate the crystallite size and the
strain (inset of Fig. 1) developed in the NF phase of the
nanocomposite and the values are found to be 7.7 nm and
18  103, respectively.
Crystallite size for Ni nanoparticles is estimated as 7 nm
from Scherrer equation by using major peak (111) FIG. 2. HRTEM of RGO-Ni/NF nanocomposite at a scale of 50 nm (a) and
2 nm (b).
D ¼ 0:9k=b cos h;

where D ¼ crystallite size, k ¼ wavelength of X-rays used, properties.22 The physical origin of magnetism can also be
and h ¼ Bragg’s angle. due to the localized states, which arise at the Fermi level of
We have very recently reported multiple magnetic inter- graphene due to the distortion in the lattice. Thus, the local
actions in graphene.22 The temperature, magnetic field moments exist by electron-electron interactions and these
(externally applied), the spin density along the graphene moments interact ferromagnetically.23 Missing of atoms or
edges, and the interactions among them are the deciding fac- voids can be the another type of source for the magnetism in
tors for the magnetism in graphene. The dominating factors graphene.24 Fig. 3 shows the temperature dependent magnet-
could be paramagnetic centers/density of edge states and ization of RGO under different field starting from 100 Oe to
interactions among them. For an evidence ESR (Electron 2000 Oe. This is the material that we have used in the nano-
Spin Resonance) studies have shown that the localized spins composite of RGO-Ni/NF. The XPS data show the presence
in exfoliated graphene are responsible for observed magnetic of carbon and oxygen only and there are no other peaks cor-
responding to any magnetic impurities, see the

FIG. 1. XRD of RGO-Ni/NF nanocomposite. FIG. 3. ZFC-FC curves for RGO.

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 86.4.50.211
On: Sun, 10 Aug 2014 16:01:08
 052412-3 Kollu et al. Appl. Phys. Lett. 105, 052412 (2014)

supplementary material S2 for graph.34 Zero Field Cooled-

Field Cooled (ZFC-FC) curves represent magnetic behavior
of RGO and there is a divergence between them. This typical
feature suggests the presence of ferromagnetic (FM) and
antiferromagnetic (AFM) spin states on graphene25 and in
our previous studies, we have reported the typical ferromag-
netic nature of RGO.19,22 On increase in applied field value,
FM correlation dominates AFM interaction and divergence
between ZFC, FC curves decreases (inset of Fig. 3) under
sub ambient temperatures. Recent theoretical calculations
support this assumption.9,25 At low field (100 Oe and
200 Oe), ZFC-FC curves show positive magnetic moment
values up to the room temperature but at higher field (500 Oe
and 2000 Oe) there is a transition to diamagnetic state show-
ing negative magnetic moment. Since, the magnetic behavior
resembles frustrated spin system, the transition temperature FIG. 4. ZFC-FC curves for RGO-Ni/NF nanocomposite.
is not sharp, and it is evident from Fig. 3 which shows the
transition temperature from 60 K to 100 K. Such type of sim-
purpose of nanocomposite also shows signature of FM and
ilar behavior along with room temperature ferromagnetic na-
AFM regions as we have discussed with the help of Fig. 3. In
ture for exfoliated graphene is earlier reported.10 The TEM
superparamagnetic nanoparticles (Ni and NF) individually,
image of as prepared RGO is shown as S1, see the supple-
canting of core and surface spin structures have also been
mentary material for image.34
understood clearly.12,13 Apparently, the composite compris-
Bulk NF possesses inverse spinel structure. Site occupa-
ing of these materials, under sufficiently low fields competes
tion in inverse spinel is out of 64 tetrahedral sites 8 are occu-
with various interactions of FM, AFM, and canted spin struc-
pied by Feþ3 and out of 32 octahedral sites 16 (8 Niþ2, 8
tures. These interactions on an average may turn into frus-
Feþ3) are occupied equally by Niþ2, Feþ3. In case of nano-
trated spin system giving signals in the form of anomalous
ferrite, the distribution may change from inverse spinel to
behavior of temperature dependent magnetization curves,
mixed spinel structure facilitating the Niþ2 nanoparticles to
showing higher ZFC values to that of FC under 100 Oe and
occupy tetrahedral sites. On tetrahedral sites, the orbital mag-
200 Oe. This similar type higher ZFC to FC behavior has
netic moment of Niþ2 is not quenched and lead to the
been previously reported by Chinnasamy et al. for nanocrys-
magneto-crystalline anisotropy. This magneto-crystalline an-
talline NF.12 The frustrated spin behavior at low fields was
isotropy causes canted spin structures for the core,12 and it is
also observed by the M-H loops, shown in Fig. 5.
also known that broken bonds cause surface spin canting for
Fig. 5 shows the field dependent magnetization behavior
reduced dimensionality of nanoparticles.13 Therefore, NF
of RGO-Ni/NF nanocomposite under a maximum field of
nanoparticles can have a core of ferrimagnetically interacting
100 Oe at different temperatures (M-H curves). Magnetization
canted spins which is surrounded by shell of disordered spins,
loops at all temperature show irregular (zigzag region in M-H
i.e., spin-glass like surface layer.13,26 Previously reported
curves) region of positive and negative moment with respect to
Mossbauer studies also revealed the existence of canted sur-
the applied field and the extent of zigzag region is not same on
face spin structure of Feþ3 for NF nanoparticles.12,27
both sides of field dependent magnetization curves.
In RGO-Ni/NF nanocomposite RGO sheets are crumpled
In RGO-Ni/NF nanocomposite, it was observed that,
around the magnetic nanoparticles, and Ni/NF nanoparticles
there were interactions among the canted spins of core (due to
are uniformly adsorbed on graphene sheets (Fig. 2). Ni, NF
magneto-crystalline anisotropy) and disordered spins of
nanoparticles in the composite are having average particle
size around 7 nm and 7.7 nm, respectively. These are the typi-
cal sizes for these magnetic particles to possess superpara-
magnetism.28,29 Ni nanoparticles can also possess surface
spin disorder.21 Fig. 4 represents the temperature dependent
magnetization of RGO-Ni/NF nanocomposite (ZFC-FC)
under different applied fields starting from a low field of
100 Oe to a maximum of 5000 Oe. These curves show the
variation in blocking temperature from 110 K for 100 Oe to
30 K for 1000 Oe. Applied field above 1000 Oe can suffi-
ciently overcome the blocking effects and results in overlap-
ping of ZFC-FC curves. For field values around 100 Oe and
200 Oe, there is an anomaly in ZFC-FC behavior showing
higher ZFC values to that of FC. To understand this peculiar
behavior, we should consider the various possible magnetic
interactions in the nanocomposite under low fields.
The coexistence of FM and AFM region for graphene
are well reported,10,22 and the pristine RGO prepared for the FIG. 5. M-H loops for RGO-Ni/NF nanocomposite at various temperatures.

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 86.4.50.211
On: Sun, 10 Aug 2014 16:01:08
 052412-4 Kollu et al. Appl. Phys. Lett. 105, 052412 (2014)

surface of Ni, NF (due to broken bonds) nanoparticles in addi- Authors acknowledge SAIF/CRNTS, IIT Bombay for
tion to FM and AFM interactions from RGO. We have earlier characterization facilities and Dr. Pratap Kollu
reported the FM and AFM correlations in graphene.22 These acknowledges DST-INSPIRE Faculty Award (2012–2017).
interactions among various components of nanocomposite
may result in complex stochastic spin behavior, i.e., at lower 1
applied field values (100 Oe) at all temperatures there exist A. K. Geim and K. S. Novoselov, Nat. Mater. 6, 183 (2007).
2
K. S. Novoselov, V. I. Fal0 ko, L. Colombo, P. R. Gellert, M. G. Schwab,
some value of field region where thermal energy for the spin and K. Kim, Nature 490, 192 (2012).
of Ni, NF nanoparticles is not sufficient to overcome its intrin- 3
E. Cobas, A. L. Friedman, O. M. J. van’t Erve, J. T. Robinson, and B. T.
sic anisotropy to align with the applied field, and further there Jonker, Nano Lett. 12, 3000 (2012).
4
J. Liang, Y. Xu, D. Sui, L. Zhang, Y. Huang, Y. Ma, F. Li, and Y. Chen,
is an interaction with the FM and AFM regions arising from
J. Phys. Chem. C 114, 17465 (2010).
RGO with disordered surface spin of Ni/NF nanoparticles. 5
J. Zhu, Z. Luo, S. Wu, N. Haldolaarachchige, D. P. Young, S. Wei, and Z.
Therefore, there exist some competences among various inter- Guo, J. Mater. Chem. 22, 835 (2012).
6
actions with different stochastic spin configurations, which Y. Fu, Y. Wan, H. Xia, and X. Wang, J. Power Sources 213, 338 (2012).
7
W. Zhu, L. Wang, R. Zhao, J. Ren, G. Lua, and Y. Wang, Nanoscale 3,
may lead to the negative and positive moment of RGO-Ni/NF
2862 (2011).
nanocomposite under low applied fields. In all M-H loops, 8
S.-Q. Liu, B. Xiao, L.-R. Feng, S.-S. Zhou, Z.-G. Chen, C.-B. Liu, F.
with increase in temperature the extent of zigzag region comes Chen, Z.-Y. Wu, N. Xu, W.-C. Oh, and Z.-D. Meng, Carbon 64, 197
down and show typical superparamagnetic behavior with (2013).
9
J. H. Sun, F. M. Hu, H. K. Tang, W. Guo, and H. Q. Lin, J. Appl. Phys.
almost zero remanence. This may be due to a decrease in the 113, 17B515 (2013).
number of stochastic spin configuration with increase in tem- 10
H. S. S. Ramakrishna Matte, K. S. Subrahmanyam, and C. N. R. Rao,
perature by overcoming anisotropic energy of the RGO-Ni/NF J. Phys. Chem. C 113(23), 9982 (2009).
11
system to some extent. Cyclic M-H loops drawn under various L. Chen, L. Guo, Z. Li, H. Zhang, J. Lin, J. Huang, S. Jin, and X. Chen,
Sci. Rep. 3, 2599 (2013).
field sweeping values and the AC Magnetic 12
C. N. Chinnasamy, A. Narayanasamy, N. Ponpandian, K. Chattopadhyay,
Susceptibility(ACMS) measurements under 4 Oe supports this K. Shinoda, B. Jeyadevan, K. Tohji, K. Nakatsuka, T. Furubayashi, and I.
proposed explanation, see supplementary material S3 and S4 13
Nakatani, Phys. Rev. B 63, 184108 (2001).
for ACMS and cyclic M-H curves.34 R. H. Kodama, A. E. Berkowitz, E. J. McNiff, Jr., and S. Foner, Phys.
Rev. Lett. 77(2), 394 (1996).
Graphene based devices are technologically important. 14
I. Zanella, S. B. Fagan, R. Mota, and A. Fazzio, J. Phys. Chem. C 112,
Recently, water soluble and magnetic functionalized reduced 9163 (2008).
15
graphene oxide for magnetic resonance imaging (MRI) R. H. Kodama, A. E. Berkowitz, E. J. McNiff, Jr., and S. Foner, J. Appl.
applications has been introduced.30 For spintronics applica- Phys. 81(8), 5552 (1997).
16
A. E. Berkomitz, J. A. Lahut, I. S. Sacobs, L. M. Levinson, and D. W.
tions, Wang et al.31 proposed that the topological frustration Forester, Phys. Rev. Lett. 34(10), 594 (1975).
or size effects can lead to the magnetic ordering in graphene 17
A. Kumar Swain and D. Bahadur, RSC Adv. 3, 19243 (2013).
18
related structures, and they have been introduced a rigorous S. Bai, X. Shen, X. Zhong, Y. Liu, G. Zhu, X. Xu, and K. Chen, Carbon
50, 2337 (2012).
classification schemes for the graphene to have large net spin 19
P. K. Sahoo, B. Panigrahy, D. Li, and D. Bahadur, J. Appl. Phys. 113,
or AFM correlations. In high density ultrafast spintronics, 17B525 (2013).
20
these topological schemes with AFM correlations are desired M. Fu, Q. Jiao, and Y. Zhao, J. Mater. Chem. A 1, 5577 (2013).
21
to create spin based fundamental logic gates like NOR and S. Vitta, J. Appl. Phys. 101, 063901 (2007).
22
A. Kumar Swain and D. Bahadur, Appl. Phys. Lett. 104, 242413 (2014).
NAND. Hidden multiferroic ordering has been proposed for 23
M. A. H. Vozmediano, M. P. L opez-Sancho, T. Stauber, and F. Guinea,
graphene nanoribbons with zigzag edges,32 and the NF based Phys. Rev. B 72, 155121 (2005).
24
composites have been reported for multiferroic applica- J. J. Palacios and J. Fernandez-Rossier, Phys. Rev. B 77, 195428 (2008).
25
tions.33 In near future, the composites of graphene-Ni/NF 26
S. Dutta, S. Lakshmi, and S. K. Pati, Phys. Rev. B 77, 073412 (2008).
V. Sepelak, I. Bergmann, A. Feldhoff, P. Heitjans, F. Krumeich, D.
may work for multiferroic applications. Therefore, in view Menzel, F. J. Litterst, S. J. Campbell, and K. D. Becker, J. Phys. Chem. C
of above applications which involve the spin structures, the 111, 5026 (2007).
27
present work of “anomalous magnetic properties of RGO-Ni/ 28
A. H. Morr and K. Haneda, J. Appl. Phys. 52, 2496 (1981).
NF” has got importance and emphasizes to consider various M. Gaboardi, A. Bliersbach, G. Bertoni, M. Aramini, G. Vlahopoulou, D.
Pontiroli, P. Mauron, G. Magnani, G. Salviati, A. Z€ uttel, and M. Ricc
o,
possible interactions in graphene based magnetic composites J. Mater. Chem. A 2, 1039 (2014).
for possible device applications. 29
F. C. Fonseca, G. F. Goya, R. F. Jardim, R. Muccillo, N. L. V. Carreno, E.
In the summary, by using one pot solvothermal synthesis Longo, and E. R. Leite, Phys. Rev. B 66, 104406 (2002).
30
RGO-Ni/NF nanocomposite material have been synthesized. H.-P. Cong, J.-J. He, Y. Lu, and S.-H. Yu, Small 6(2), 169 (2010).
31
W. L. Wang, O. V. Yazyev, S. Meng, and E. Kaxiras, Phys. Rev. Lett.
ZFC-FC measurements of the material show spin-glass like 102, 157201 (2009).
behavior with a peculiar phenomenon of ZFC magnetization 32
J. Fernandez-Rossier, Phys. Rev. B 77, 075430 (2008).
33
values greater than the FC magnetization values. The M. Liu, X. Li, H. Imrane, Y. Chen, T. Goodrich, Z. Cai, K. S. Ziemer, J.
Y. Huang, and N. X. Sun, Appl. Phys. Lett. 90, 152501 (2007).
observed anomalous behavior for field dependent and tem- 34
See supplementary material at http://dx.doi.org/10.1063/1.4892476 for
perature dependent magnetization was effectively explained TEM of RGO, XPS of RGO, ACMS of RGO-Ni/NF, and Cyclic M-H
on the basis of possible canted spin structures. loops of RGO-Ni/NF at the link.

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 86.4.50.211
On: Sun, 10 Aug 2014 16:01:08