Theoretical approach to defect-induced magnetism in oxygen-deficient γ-Ga2O3 films

Abstract

Gallium oxide (Ga2O3) is an emerging material with several known polymorphs that exhibit many interesting properties for applications. In this work is theoretically studied and discussed the unconventional ferromagnetism observed in oxygen-deficient thin films of Ga2O3-x (0.42 < x < 0.60) grown on sapphire substrates. The formation of the magnetic moments is demonstrated in good agreement with experimental magnetization measurements using first-principles calculations based on the density functional theory performed for a standard crystal structure of γ-Ga2O3 with oxygen vacancies in different configurations. The random distribution of pairs of oxygen vacancies and rearrangements of them within the spinel-like cubic structure containing tetrahedral and octahedral sites for increasing temperatures are consistent with long-range persistent non-collinear magnetic order up to temperatures that may be exceed the temperature at which full conversion of γ-Ga2O3 to β-Ga2O3 takes place. Our present results also reveal that magnetic irreversibility observed from 10 K to room temperature are possibly determined by the intrinsic disorder in the structure of tetrahedral and octahedral sites that allows numerous possible paths for the migration of oxygen vacancies with low values of activation energies and migration barriers, as indicated by the previously published reports.