Site preference, magnetic properties and energy band gap of SrFe12−xInxO19

Abstract The nonmagnetic In3+ doping in the hexagonal SrFe12−xInxO19 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 1 and 2) permanent magnet increases the saturation magnetization at 300 K with the highest value up to 73.87 emu/g at x = 0.5, and decreases it with x > 0.5. The coercive field keeps almost the same for x ≤ 0.2, but it decreases with x > 0.2. The Curie temperature linearly decreases from 740 K for x = 0 to 610 K for x = 1.0, and decreases at a much lower rate to 592 K for x = 2.0. The XPS, FT-IR and UV–vis spectra are carried out to characterize the relations between the magnetic properties and the structure. The In3+ ions preferentially occupy the tetragonal 4f1 site, deduced from the xrd refinement and the FT-IR spectra. It is consistent with the increasing magnetization by the In3+ doping. Oxygen vacancies exist in the compounds. The In3+ doping and oxygen vacancies deteriorate the coercivity, while Fe2+ ions are in favor of a high magnetocrystalline anisotropy. The energy band gap of SrFe12−xInxO19 increases with the increasing In3+ doping from 1.75 eV for x = 0 to 1.87 eV for x = 1.0, but that of x = 2.0 decreases to 1.79 eV. It reflects that oxygen vacancies in x = 2.0 play a function on the energy band gap.