Abstract
During slow oxidation of magnetite powder in the air, we can obtain Fe3O4-γ⋅Fe2O3 solid solutions. There are expressed in the formula ?? x/3Fe3-x/3O4, where ?? is the cation vacancy and (x) is the degree of oxidation. The composition which corresponds to (x)=0.65 shows an abnormal increase in coercive force. After the sample is prepared, its coercive force increases gradually ; this phenomenon is a kind of aging effect.
The present author tries to describe this abnormal phenomenon of magnetic properties and discuss the origin and mechanism of the effects. The author applies the "nucleation model" to the aging effect. The oxidation does not proceed uniformly in the magnetite particle and some structural defects act as the nuclei of oxidation. These nuclei behave supermagnetically when their sizes are small, but, when they grow up to the range of single domain size, their coercive force increases. The aging effect takes place by the diffusion of ferric ions, cation vacancies and electrons. The activation energy for ion diffusion decreases because this solid solution is an electron conductive substtance. Further experiments and discussions will be published.
