Magnetic ordering and exchange interactions in multiferroic GaFeO₃

We report our first-principles calculations on multiferroic GaFeO₃. The total energy results for different spin and structural configurations reveal that the ground state of GaFeO₃ in its ideal structure is antiferromagnetic but it is likely to have a possible site disorder of Fe and Ga atoms between octahedral Ga sites and Fe sites, which is consistent with previous experimental observations. Examining the exchange interactions among Fe atoms at either Ga or Fe sites in GaFeO₃, we conclude that the net magnetic moments observed in experiments may arise from Fe atoms occupying the Ga sites. Despite the d⁵ configuration of Fe ions in GaFeO₃, significant orbital magnetic moments are found to exist and their origin is attributed to the local distortion of oxygen octahedra as well as the Fe off-centering present in the system.