Effect of Powder Grain Size on Microstructure and Magnetic
Properties of Hexagonal Barium Ferrite Ceramic
LI-HUAN SHAO,
1
SI-YUN SHEN,
1
HUI ZHENG ,
1,3
PENG ZHENG,
1
QIONG WU,
2
and LIANG ZHENG
1
1.—Institute of Electron Device & Application, Hangzhou Dianzi University, Hangzhou 310018,
China. 2.—Magnetism Key Laboratory of Zhejiang Province, China Jiliang University,
Hangzhou 310018, China. 3.—e-mail: zhenghui0551@126.com
Compact hexagonal barium ferrite (BaFe
12
O
19
, BaM) ceramics with excellent
magnetic properties have been prepared from powder with the optimal grain
size. The dependence of the microstructure and magnetic properties of the
ceramics on powder grain size was studied in detail. Single-phase hexagonal
barium ferrite powder with grain size of 177 nm, 256 nm, 327 nm, and 454 nm
was obtained by calcination under different conditions. Scanning electron
microscopy revealed that 327-nm powder was beneficial for obtaining homo-
geneous grain size and compact ceramic. In addition, magnetic hysteresis
loops and complex permeability spectra demonstrated that the highest satu-
ration magnetization (67.2 emu/g) and real part of the permeability (1.11) at
1 GHz were also obtained using powder with grain size of 327 nm. This
relationship between the powder grain size and the properties of the resulting
BaM ceramic could be significant for development of microwave devices.
Key words: Hexagonal barium ferrite, ceramic, microstructure, magnetism
INTRODUCTION
Recently, millimeter (mm)-wave devices, which
operate in the frequency range from approximately
30 GHz to 100 GHz, have attracted significant
attention.
1–3
Such devices include circulators, fil-
ters, resonators, isolators, and phase shifters, which
have contributed significantly to development of
microwave technology. In principle, one could
extend this operating frequency range from the
microwave to mm-wave range by application of high
external magnetic bias fields.
4–7
However, use of
such high external fields is usually impractical due
to increased device size and weight.
One effective strategy for such frequency exten-
sion is use of M-type barium hexagonal ferrite
(BaFe
12
O
19
, BaM), which has a very high magne-
tocrystalline anisotropy field.
8,9
This high internal
field can increase the ferromagnetic resonance and
hence enable device operation at mm-wave
frequencies.
The traditional process for preparing BaM ceramic
mainly involves obtaining precursor powders, their
calcination under selected conditions, pressing the
resulting powder into pieces, and sintering under
appropriate conditions.
10,11
The properties of such
BaM ceramic materials, including their density,
purity, grain size, and magnetic properties, are
strongly determined by the properties of the initial
BaM powder, especially its purity and grain size.
12,13
Furthermore, it is reported that single-phase mate-
rials can be achieved when using different grain sizes
of powder (GSP) obtained under different calcination
conditions.
14–17
However, few studies have system-
atically investigated the influence of the GSP on the
properties of the resulting ferrite ceramic.
In the work presented herein, BaM precursor
powder was prepared by the sol–gel method,
18–21
then calcined under different conditions. The influ-
ence of the grain size of the powder on the
microstructure and magnetic properties of the
resulting BaM ceramic was studied in detail.
(Received November 22, 2017; accepted April 11, 2018;
published online May 14, 2018)
Journal of ELECTRONIC MATERIALS, Vol. 47, No. 7, 2018
https://doi.org/10.1007/s11664-018-6301-y
Ó
2018 The Minerals, Metals & Materials Society
4085
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