Origin of coercivity changes during the oxidation of Fe3O4to γ-Fe2O3

Oxidation kinetics and x-ray diffraction of the intermediate products have been investigated for several kinds of Fe
3
O
4
powders during the oxidation to γFe
2
O
3
. From these results, a two-components-hypothesis as an intermediate state of the Fe
3
O
4
- γFe
2
O
3
system is proposed, instead of a homogenious solid solution which has been widely recognized. The effect of the changes in particle size caused by the two phases oxidation products on the variations of magnetic coercivity was emphasised.