Effect of vacancies on the coercivity of γ-Fe2O3-Fe3O4solid solutions

The variation in coercivity caused by annealing was examined for solid solution of γ-Fe2O3and Fe3O4particles represented as (1-x)Fe8/3O4. xFe3O4. The coercivity of the particles increased by annealing at temperatures of 60°C to 100°C, and the maximum coercivity was observed in particles having a vacancy content of 0.22. The activation energy of the particles was 0.3-0.6 eV which suggests the migration of cation vacancies. The increase of coercivity in annealing was considered to be due to the magnetic anisotropy induced by vacancy ordering closely related to Fe²⁺ions.