Vacancy Ordering in Epitaxially-Grown Single Crystals of γ-Fe₂O₃

Abstract

Single crystal films of γ-Fe 2 O 3 were epitaxially grown on a (100) surface of MgO by the halide-decomposition method. Chemical analysis, electrical conductivity and, optical absorption measurements showed that the crystals contain no ferrous ions. X-ray diffraction assigned a cubic spinel structure and ruled out the presence of ordering of cation vacancies. Magnetization measurement and ferromagnetic resonance experiments were performed on these films which revealed the value of saturation magnetization and the anisotropy constants. The effective Bohr magneton number per iron atom was determined to be 1.45 at 0°K, which is considerably larger than that expected from Néel's theory. The Curie temperature is 743°K, which is lower than that found in ordinary γ-Fe 2 O 3 powder. These results conclude that the vacancies at 16 d sites are randomly distributed and nearly twenty percent of the total vacancies occupy 8 a sites.