Electronic and magnetic properties ofGaFeO3:Ab initiocalculations for varying Fe/Ga ratio, inner cationic site disorder, and epitaxial strain

Abstract

In this study we present ab initio density-functional theory calculations on stoichiometric, cation-doped, and strained $\mathrm{GaFeO}{}_{3}$. We start with a detailed discussion of the origin of the antiferromagnetic (AFM) superexchange in stoichiometric $\mathrm{GaFeO}{}_{3}$ 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 $\mathrm{GaFeO}{}_{3}$ 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 ${\mathrm{Ga}}_{2\ensuremath{-}x}\mathrm{Fe}{}_{x}{\mathrm{O}}_{3}$ for varying Fe concentrations $\mathit{x}(0.0\ensuremath{\le}\mathit{x}\ensuremath{\le}2.0)$ where at a value of $\mathit{x}=0.0$ and $\mathit{x}=2.0$ it transforms into the isomorphic $\ensuremath{\varepsilon}\text{\ensuremath{-}}\mathrm{Ga}{}_{2}{\mathrm{O}}_{3}$ and $\ensuremath{\varepsilon}\text{\ensuremath{-}}\mathrm{Fe}{}_{2}{\mathrm{O}}_{3}$ 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.