Electronic and magnetic properties of GaFeO3: Ab initio calculations for varying Fe/Ga ratio, inner cationic site disorder, and epitaxial strain

In this study we present ab initio density-functional theory calculations on stoichiometric, cation-doped, and strained GaFeO3. We start with a detailed discussion of the origin of the antiferromagnetic (AFM) superexchange in stoichiometric GaFeO3 and give a molecular orbital description of the exchange mechanism derived from our calculations. In addition, we study the properties of the Fe-O-Fe bonds for different geometries to underline the angle and distance dependence of the AFM coupling as formulated in the Goodenough-Kanamori rules. We describe the AFM ground state of GaFeO3 as a result of two intrinsic Fe-O-Fe chains that meander through the crystal along the c direction. The magnetocrystalline anisotropy energies are calculated for the stoichiometric phase with and without inner cationic site disorder, and the presence of a sublattice-dependent anisotropy is examined. Furthermore, we perform our studies of Ga2-xFexO3 for varying Fe concentrations x(0.0 <= x <= 2.0) where at a value of x = 0.0 and x = 2.0 it transforms into the isomorphic epsilon-Ga2O3 and epsilon-Fe2O3 phases, respectively. The effect of strain was also studied. Incorporating dopants and applying strain to the simulation cell changes the intrinsic geometry and thus the magnetic properties of gallium ferrite.