The effect of substitution of diamagnetic Al3+ and In3+ ions for partial Fe3+ ions in a spinel lattice on the magnetic and microwave properties of magnesium-manganese (Mg-Mn) ferrites has been studied. Three kinds of Mg-Mn based ferrites with compositions of Mg0.9Mn0.1Fe2O4, Mg0.9Mn0.1Al0.1Fe1.9O4, and Mg0.9Mn0.1In0.1Fe1.9O4 were prepared by the solid-state reaction route. Each mixture of high-purity starting materials (oxide powders) in stoichiometric amounts was calcined at 1100 °C for 4 h, and the debinded green compacts were sintered at 1350 °C for 4 h. XRD examination confirmed that the sintered ferrite samples had a single-phase cubic spinel structure. The incorporation of Al3+ or In3+ ions in place of Fe3+ ions in Mg-Mn ferrites increased the average particle size, decreased the Curie temperature, and resulted in a broader resonance linewidth as compared to un-substituted Mg-Mn ferrites in the X-band. In this study, the In3+ substituted Mg-Mn ferrites exhibited the highest saturation magnetization of 35.7 emu/g, the lowest coercivity of 4.1 Oe, and the highest Q×f value of 1050 GHz at a frequency of 6.5 GHz.
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