Annealing effects on the structure and ferromagnetic
properties of as prepared Co2.25Fe0.75O4 ferrite
Manas Ranjan Panda*, and R. N. Bhowmik
Department of Physics, Pondicherry University, R. Venkataraman Nagar, Kalapet, Pondicherry-605014, India
*Corresponding author’s e-mail: manasranjan056@gmail.com,Mobile: +91-7845794468
Abstract
Experimental
The material was prepared by co-precipitation
of Co(No3)2.6H2O and Fe(NO3)3.9H2O solution in high
alkaline medium (pH  11) at 80 0C for 4 hrs. The as
prepared sample after annealing at 200 0C, 500 0C, 800
0
C, 900 0C, and 1000 0C in air for 4 hrs was denoted as
CoFe2A4, CoFe5A4, CoFe8A4, CoFe9A4, CoFe10A4.
Results
X-ray diffraction (XRD) pattern showed single
phased cubic spinel structure (a  8.200 Å) for TAN  900
0
C and splitting of the cubic spinel structure into Co rich
(a 8.095 Å - 8.122 Å) and Fe rich (a  8.302 Å - 8.327
Å) phases for other annealing temperatures. The sample
annealed at 1000 0C showed a minor trace of CoO, as
seen in earlier work [3]. Major XRD peaks were fitted
with Gaussian shape to obtain area, height, half width and
positions of the peaks. Grain size of the material varied
the range 5-25 nm by increasing TAN 200 0C to 1000 0C.
Percentage of the Co- rich and Fe-rich phases was
calculated from the peak height and area ratio after
resolving two phases using profile fitting, and shown at
different TAN in the inset (a) of Fig. 1. Raman spectra of
the samples suggested normal spinel structure (more
divalent cations in A sites and trivalent cations in B sites).
Field dependent magnetization [M(H)] curves showed
room temperature ferromagnetism in all samples. The
sample annealed at 800 0C (least Fe-rich phase in inset
(b)) showed maximum coercivity  568 Oe and also
squareness 0.33.The single phased sample shows lowest
coercivity and ferromagnetic moment.
10
Phase (%)
15
CoFe10A4
80
CoFe2A4
Fe-rich phase
CoFe8A4
60
CoFe5A4
40
CoFe9A4
Co-rich phase
5
20
200
400 600
0
TAN ( C)
800
1000
0
-5
-10
-15
Inset (b)
600
400
15
M16 kOe
HC
10
HC (Oe)
20
Single phase
Spinel ferrites are interesting for applications in
magnetic recording and electro-magnetic devices [1].
The basic need is ferromagnetism with reasonably large
spontaneous magnetization, coercivity and squareness.
These parameters are highly tunable in Co rich side (x ≥
1) of CoxFe3-xO4 [2], where ferromagnetic parameters
strongly depend on Co content, distribution of Co and Fe
ions among tetrahedral (A) and octahedral (B)
coordinated sites, and super-exchange interactions [3].
Material synthesis also played a crucial role in tailoring
ferromagnetic parameters in CoxFe3-xO4 ferrite [4, 5].
Inset (a)
100
M at 16 kOe (emu/g)
Introduction
20
Magnetization (emu/g)
Co2.25Fe0.75O4 ferrite was prepared by co-precipitation route.
Depending on annealing temperature (TAN), the as prepared
material was stabilized in single phased and bi-phased cubic
spinel structure. The samples showed ferromagnetic properties
at room temperature and ferromagnetic parameters depends on
phase formation.
200
5
20
-20
-15000
-10000
30
40
50
60
Fe rich phase (%)
-5000
0
5000
Magnetic Field (Oe)
10000
0
15000
Fig. 1. M(H) curves for different samples. Inset shows
the phase (%) with TAN (a) and variation of magnetic
parameters with Fe rich phase (b).
Conclusions
The probable cation distribution of the single phased
compound is (Coα2+Fe1-α3+)A[Co2+1-αFe3+2-x+αCo3+x-1]BO4
with x = 2.25 and α  1 (normal spinel structure). In biphased samples, cation distribution in Co-rich and Ferich phases are suggested as (Co2+)A[Fe3+0.75-Co3+1.25+]B
O4 and (Co2+)A[Fe3+0.75+Co3+1.25-]BO4, respectively. This
work suggest that ferromagnetic properties can be
tailored by controlling the single phase and bi-phased
structure of the Co rich side of CoxFe3-xO4 compound.
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), Gov. of
India.
References
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Magn. Mater. 321 (2009) 2035-2047.
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Compd. 578 (2013) 585-594.
[3] H. L. Trong et al., J. Magn. Magn. Mater. 334 (2013)
66-73.
[4] R. N. Bhowmik, A.T.Satya, A.Bharathi, J. Alloys
Compd. 559 (2013) 134-141.
[5] R.N. Bhowmik, Mater. Res. Bull. 50 (2014) 476-482.