Effects of in³⁺ site occupancy on the magnetic properties of m-type strontium hexaferrites

Effects of nonmagnetic indium ion substitution on magnetic properties of M-type strontium hexaferrites SrFe_12-xIn_xO₁₉ (x=0, 0.25, 0.5, 0.75, and 1) have been studied by crystallographic and magnetic measurements. Samples were prepared by citric auto-combustion method. Rietveld analysis of X-ray diffraction profiles showed that the samples were single phase with the space group P6₃/mmc and lattice constants a and c increased linearly with In³⁺ content. Mössbauer spectra showed that In³⁺ mainly replaced Fe³⁺ ions in 4f₂ sites and that 12k subspectra split into two distinct components 12k₁ and 12k₂. Analysis of hysteresis curves showed that while the coercive force and the magnetic anisotropy constant decreased thru the whole doping range x, the saturation magnetization first increased until x=0.5 and decreased thereafter. This behavior was explained by the existence of two competing interactions in terms of nonmagnetic indium substitution.