Structural, electronic, magnetic and optical properties of AB2O4 (A = Ge, Co and B = Ga, Co) spinel oxides

Abstract Structural, magnetic, optical and electronic properties of GeGa2O4, CoGa2O4, GeCo2O4 and CoCo2O4 spinel oxides have been studied. Spinel oxides are studied by performing theoretical calculations based on density functional theory. In non-magnetic host GeGa2O4 spinel oxide, significant effects of Co occupancy (at A, B and/or both sites) on the electronic, magnetic and optical behavior have been observed. Among the spinel oxides, the CoGa2O4, GeCo2O4 and CoCo2O4 spinel oxides show 100% spin-polarization and exhibit stable cubic structure in ferromagnetic phase. The calculated structural and magnetic parameters predict the cation distribution at A and B sites as follows: ( G e 2 + ) [ G a 2 3 + ] O 4 − 2 , ( C o 2 + ) [ G a 2 3 + ] O 4 − 2 , ( G e 4 + ) [ C o 2 2 + ] O 4 − 2 and ( C o + 2 ) [ C o 2 3 + ] O 4 − 2 for GeGa2O4, CoGa2O4, GeCo2O4 and CoCo2O4 spinel oxides, respectively. The electronic band gap is found to be decreased from 1.605 eV to 0.762 eV for spin↑ state while it is decreased from 1.578 eV to 0.000 eV for spin↓ state with Co occupancy in host GeGa2O4 lattice. Lattice constant decreases (8.7877 A to 8.1390 A) as Co occupies B site and/or both (A and B) sites. For GeCo2O4 spinel oxide, the calculated value of total magnetic moment (mtot = 6.12 μ B /f.u) and saturation magnetization (MS = 134.22 emu/g) is found to maximum. Optical properties reveal that the CoGa2O4, GeCo2O4 and CoCo2O4 spinel oxides have less threshold electronic transition energy relative to host GeGa2O4 spinel oxide. Electronic, magnetic and optical characteristics show potential integration of these spinel oxides in magnetic-semiconducting devices.