The synthesis and characterization of the hexagonal Z
ferrite, Sr
3
Co
2
Fe
24
O
41
, from a sol-gel precursor
R.C. Pullar
1
, A.K. Bhattacharya*
Warwick Process Technology Group, School of Engineering, University of Warwick, Coventry CV4 7AL, UK
(Refereed)
Received 28 September 2000; accepted 17 January 2001
Abstract
The Z ferrite Sr
3
Co
2
Fe
24
O
41
, produced from a stoichiometric aqueous inorganic sol-gel precursor,
is reported and its magnetic hysteresis loop characterized for the first time. The precursor was an
iron(III)hydroxide sol stabilised with NO
3
-
counterions and doped with stoichiometric nitrate salts,
which had a particle size similar to halide stabilised Ba
3
Co
2
Fe
24
O
41
Z ferrite precursor sols investi-
gated previously. When fired the amorphous gel formed a mixture of -Fe
2
O
3
, BaM and CoFe
2
O
4
from 600°C, but these products then converted directly to the pure Z phase at 1200°C, without first
forming the Y ferrite (Ba
2
Co
2
Fe
12
O
22
) phase always observed prior to Z ferrite crystallization in
Ba
3
Co
2
Fe
24
O
41
systems. The resulting material was a very soft ferrite, with a very low coercivity of
5.6 kA m
-1
and a magnetisation of 48.5 emu g
-1
at an applied field of 5 T. © 2001 Elsevier Science
Ltd. All rights reserved.
Keywords: A. Magnetic materials; B. Sol-gel chemistry; D. Magnetic properties
1. Introduction
The Z ferrites are one of the family of hexagonal ferrites discovered by researchers with
Philips in the late 1950s, and have the composition Ba
3
Me
2
Fe
24
O
41
, where Me = a transition
metal
2+
ion [1]. The Z ferrites all have a uniaxial anisotropy parallel to the c-axis, except
* Corresponding author. Fax: +44-207-815-7599.
E-mail addresses: akb@warwick.ac.uk (A.K. Bhattacharya); r.c.pullar@sbu.ac.uk (R.C. Pullar).
1
Now with the Centre for Physical Electronics and Materials, School of Electrical, Electronic and Information
Engineering, South Bank University, 103 Borough Road, London SE1 0AA UK.
Pergamon Materials Research Bulletin 36 (2001) 1531–1538
0025-5408/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0025-5408(01)00596-7