Effects of Fe occupancy on physical properties of non-magnetic GeGa2O4 spinel oxide

This study investigated the structural, elastic, electronic, thermal, magnetic, and optical behavior of GeGa2O4, FeGa2O4, GeFe2O4, and FeFe2O4 spinel oxides based on ab-initio calculations. The results showed that the nonmagnetic spinel oxide GeGa2O4 exhibited remarkable physical properties due to Fe occupancy at different lattice sites within the spinel lattice. The Fe containing spinel oxides (FeGa2O4, GeFe2O4, and FeFe2O4) were found to be stable in the magnetic phase in contrast to the host GeGa2O4 spinel oxide. The spin polarizations of FeGa2O4, GeFe2O4, and FeFe2O4 oxides were calculated as 98.5%, 98.4%, and 100%, respectively. Analysis of the elastic and mechanical properties showed that all of the spinel oxides followed the Born and Huang criteria for mechanical stability. The highest Debye temperature (theta D = 663.77 K) was determined for the FeGa2O4 spinel oxide. For GeGa2O4, FeGa2O4, GeFe2O4, and FeFe2O4 oxides, the calculated structural parameters (cation-anion bond lengths and average values of tetrahedral and octahedral radii) predicted the following cation distributions among the A and B atomic sites: (Ge2+)[Ga-2(3+)]O-4(-2), (Fe2+)[Ga-2(3+)]O-4(-2), (Ge4+)[Fe-2(2+)]O-4(-2), and (Fe+2)[Fe-2(3+)]O-4(-2). The calculated electronic structures indicated that the host GeGa2O4 spinel oxide and FeFe2O4 spinel ferrite were semi-conducting and half-metallic ferromagnetic, respectively, whereas FeGa2O4 and GeFe2O4 oxides exhibited semi-metallic behavior. The GeFe2O4 spinel oxide was found to have the highest saturation magnetization (185.79 emu g(-1)) and total magnetic moment (8.26 Sigma(B) fu(-1)). The calculated optical properties indicated the suitability of these oxides for use in optical filters and sensors. The electronic and magnetic characteristics of these spinel oxides with excellent thermal and elastic stability suggest that they have potential uses in diluted magnetic semiconductor devices.