Exchange bias effect in Co1.75Fe1.25O4 spinel oxide
S. Kazhugasalamoorthy1*, R.N. Bhowmik1, and R.Ranganathan2
1
Department of Physics, Pondicherry University, R. V Nagar, Kalapet, Pondicherry-605014, India.
2
CMP division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-64, India
Corresponding author’s e-mail:skmoorthy08@yahoo.co.in, Tel.: +91-9942352426
1*
Abstract
We prepared single phased and bi-phased Co1.75Fe1.25O4 spinel
oxide by air annealing of as-prepared samples at different
temperatures. We confirmed magnetic exchange bias effect
from zero field cooled (ZFC) and field cooled (FC) magnetic
loops at 5 K. The results suggest a strong interfacial magnetic
coupling in Co rich ferrite.
from 34.82 emu/g (ZFC) to 36.26 emu/g (FC). The
exchange bias shift, ΔHC= (HC(FC)- HC(ZFC)), in
sample Co1.75_9 is significantly large (1758 Oe).
40
Keywords: Co rich ferrite, Chemical route, Exchange
bias.
Experimental
The samples were prepared by chemical co-precipitation
of stoichiometric Co(NO3)2.6H2O and Fe(NO3)3.9H2O
solutions in highly alkaline medium (pH  11) using
NaOH as precipitating agent. The final product of ferrite
powder was cleaned and annealed at temperatures 200
˚C, 500 ˚C, 800 ˚C, 900 ˚C and 1100 ˚C and the samples
were denoted as Co1.75_2, Co1.75_5, Co1.75_8,
Co1.75_9 and Co1.75_11, respectively. The phase
formation of the samples was studied by XRD pattern.
Magnetic measurements were carried out using PPMS
(Quantum Design, USA) under ZFC and FC mode.
Results and discussion
XRD pattern of the samples is consistent with
cubic spinel structure. The sample annealed at 900˚C
showed single phase; otherwise, the samples annealed at
different temperatures showed coexistence of two spinel
(Co rich and Fe rich) phases. We noted some interesting
features from ferromagnetic loops measured at 5 K (Fig.
1). First, mixed phased samples are magnetically harder
than the single phased sample. Second, all the samples
exhibited exchange bias effect (shift of FC loop with
respect to ZFC loop) both horizontal (field) and vertical
(magnetization) directions. For example, coercivity of
Co1.75_9 sample increased from 6495 Oe (ZFC) to
8253 Oe (FC), and remanent magnetization increased
M (emu/g)
Introduction
Co ferrite is an inverse spinel with cations distribution
(Fe3+)A[Co2+Fe3+]BO4 in A and B sites [1]. Further
replacement of Fe by Co atoms in Co ferrite affect the
structural phase stability, distribution of cations and
subsequently, magnetic exchange interactions both in A
and B sites of the cubic spinel structure [1-3]. We
studied a typical composition Co1.75Fe1.25O4 in Co rich
side of ferrite to study the exchange bias effect [4].
40
Co1.75_2_ZFC
Co1.75_2_FC
20
20
0
0
-20
-20
-40
40
-40
40
Co1.75_9_ZFC
Co1.75_9_FC
20
20
0
0
-20
-20
-40
-40000
-20000
0
20000
-40
40000 -40000
Co1.75_8_ZFC
Co1.75_8_FC
Co1.75_11_ZFC
Co1.75_11_FC
-20000
0
20000
40000
H (Oe)
FIG. 1: FC-ZFC loop for Co1.75Fe1.25O4 samples at 5 K.
Conclusions
The observed exchange bias effect seems to be
intrinsic of this compound and not due to splitting
of cubic spinel structure in to two phases. This is
confirmed from the fact that single phased sample
showed largest exchange bias effect. The material
can be used in magnetic recording media.
Acknowledgment
We thank to CIF, Pondicherry University and RRCAT
Indore for material characterization. We acknowledge
the Research grant from BRNS (No. 2011/37P/45/
BRNS/2628) and UGC (No. 42-804/2013 (SR), Govt. of
India.
References:
[1] I.P. Muthuselvam, and R.N. Bhowmik, Solid State
Sci. 11 (2009) 719–725.
[2] Y. Zhang et al., J. Magn. Magn. Mater. 322 (2010),
3470–3475.
[3] R.N. Bhowmik, V. Vasanthi, and A. Poddar, J.
Alloys Compd. 578 (2013) 585–594.
[4] J. Nogues et al., Phys. Reports 422 (2005) 65- 117.