Anisotropy line broadening and related problems in polycrystalline NiFe2O4

Ferrimagnetic resonance line width in slowly cooled and quenched samples of polycrystalline NiFe
2
O
4
has been measured in the
X
band in the range 4.2 to 373°K. Results confirm that the porosity contribution to the line width is best described by the relation
\Delta H_{p} = [K.4 \pi M/(V/\upsilon) + 1)]
with
K = 1
, though this overestimates
\Delta H_{p}
in certain cases. The anisotropy contribution to the line width according to Schlömann is
\Delta H_{a} = C \cdot H_{a^{1}}/4 \pi M
, with
C \cong 2.07
when
H_{a}\ll 4
M. But our results show that
C
depends upon the sign of K
1
. For
K_{1} < 0, C = 2.5
and for
K_{1} > 0 , C \cong 1.2
in range
180 Oe \leq K/M \leq 360
Oe. For very low values of
K_{1}/M
,
C
deviates very much from 2, and particularly so for
K_{1} < 0
. The effect of K
2
is shown to be negligible. Hence the result is interpreted in terms of an effective anisotropy field which takes into account the magnetoelastic energy as well.