Investigation on phase evolution in the processing of nano-crystalline
cobalt ferrite by solid-state reaction route
Hamid Akbari Moayyer
a
and Abolghasem Ataie
b
*
School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O.
Box 14395-553, Tehran, Iran
a
h_akbari@ut.ac.ir, *
b
aataie@ut.ac.ir
Keywords: Cobalt ferrite, Nano-crystallite, Synthesis, Calcination temperature
Abstract. Cobalt ferrite nano-crystalline powder was synthesized from the powder mixture of
cobalt carbonate and iron oxide by mixed oxide ceramic method. The effects of temperature of
calcination as well as molar ratio of CoCO
3
/Fe
2
O
3
on the phase structure, morphology and magnetic
properties of the products were studied using X-ray diffraction (XRD), field emission scanning
electron microscopy (FESEM) and vibrating sample magnetometer (VSM) techniques, respectively.
The samples calcined at 800 and 900˚C consisted of cobalt ferrite, iron oxide and cobalt oxide. In
the sample calcined at 1000˚C, the reaction was completed and single phase CoFe
2
O
4
with a mean
crystallite and particle sizes of 49 and 300 nm, respectively was obtained. The above sample
showed hard magnetic behavior with a coercivity of 337 Oe, saturation magnetization of 76 emu/g
and remanence of 19 emu/g.
Introduction
Cobalt ferrite, CoFe
2
O
4
, has shown a growing interest in recent years due to its specific magnetic
and electrical properties. Cobalt ferrite with a spinel structure is magnetically hard and belongs to
ferrimagnetic materials [1]. High coercivity, moderate saturation magnetization [2], high chemical
stability and good mechanical hardness [3] make it a proper candidate for wide range of
applications such as high density magnetic recording media, microwave devices and medical
diagnostics [2,4,5].
In recent years, different techniques have been employed to synthesize cobalt ferrite [2,6,7].
However, conventional calcination method is widely used in industries due to its simplicity and
good controllability of synthetic steps and low cost of starting materials.
In this study, cobalt ferrite nano-crystalline powder was synthesized by mixed oxide ceramic
method. The effects of synthesis parameters such as temperature of calcination and molar ratio of
CoCO
3
/Fe
2
O
3
on the product characteristics were investigated.
Experimental
The starting chemical analytical grade Fe
2
O
3
(from Merck Company) and CoCO
3
(from VWR
Company) have been mixed according to the stoichiometric ratio as presented in Eq. 1. Moreover,
ratio of CoCO
3
/Fe
2
O
3
was chosen 1.1 to study the effects of deviation from stoichiometry. The
mixture was ground using mortar and pestle for 20 minutes and then calcined at 700, 800, 900, 1000
and 1100˚C for 6 hours in air.
CoCO
3
+ Fe
2
O
3
→ CoFe
2
O
4
+ CO
2
(1)
XRD (Philips PW-3710) using Cu-Kα radiation was used to investigate the phase composition of
the samples. The mean crystallite size of the calcined powders was calculated by Scherrer method
which is expressed as Eq. 2:
Advanced Materials Research Vol. 829 (2014) pp 767-771
Online available since 2013/Nov/15 at www.scientific.net
© (2014) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.829.767
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