Magnetic anisotropy of cobalt-doped gamma ferric oxide

The relative remanence and the remanence coercivity of acicular single domain cobalt-doped gamma ferric oxide particles have been measured as a function of temperature and cobalt concentration. In addition, the magnetocrystalline anisotropy field of the same material has been measured separately on cubic shaped particles in the temperature range of 140-420°K and over a concentration range of 1.5- 14.5 wt % Co. The relative remanence of the acicular particles increases strongly with decreasing temperature below a temperature T
K
at which the ratio of shape to magnetocrystalline anisotropy is 0.86. T
K
is independent of a partial alignment of the particles. At temperatures below T
k
, the remanence coercivity H
R
is found to follow reasonably well Néel's relation for crystalline anisotropy, H
K
= 0.32 H
K
.