A First-Principles Study of Structure-Property Correlation and the Origin of Ferrimagnetism in Gallium Ferrite

摘要

A first-principles study of structure property correlation and the origin of ferrimagnetism is presented based on LSDA+U method. In particular, the results for the ground state structure, electronic band structure, density of states, Born effective charges, spontaneous polarization and cationic disorder are discussed. The calculations were done using Vienna ab-initio simulation package (VASP) with projector augmented wave method. We find that the ground state structure is orthorhombic and insulating having A-type antiferro-magnetic spin configuration. The cationic disorder is found to play an important role. Although the cationic site disorder is not spontaneous in the ground state, interchange of octahedrally coordinated Ga2 and Fe2 sites is most favored. We find that ferrimagnetism in gallium ferrite is primarily due to this exchange between Ga-Fe sites such that Fe spins at Ga1 and Ga2 sites are antiferromagnetically aligned while maintaining ferromagnetic coupling between Fe spins at Ga1 and Fe1 sites as well as between Fe spins at Ga2 and Fe2 sites. Further, the partial density of states shows noticeable hybridization of Fe 3d, Ga 4s, Ga 4p and O 2p states indicating some covalent character of Ga/Fe-O bonds. However, the charge density and electron localization functions show largely the ionic character of these bonds. Our calculation predicts spontaneous polarization of ～59 μC/cm~2 along b-axis.