Investigation of structural and magnetic properties of polycrystalline Ni_0.50Zn_0.50-xMg_xFe₂O₄ spinel ferrites

The structural and magnetic properties of Mg substituted Ni_0.50Zn_0.50-xMg_xFe₂O₄ (where x = 0.0, 0.10, 0.20, 0.30, 0.40 and 0.50) sintered at various temperatures have been studied thoroughly. X-ray diffraction patterns of the samples showed single-phase cubic spinel structure without any detectable impurity phases. The lattice parameter decreases linearly with increase of Mg contents obeying Vegard's law. The bulk density, average grain size and initial permeability, μ_i^′, decrease with increasing Mg substitution but increase with increasing sintering temperature for a particular composition. The highest initial permeability and quality factor, Q, are obtained for the Ni_0.50Zn_0.50Fe₂O₄ sintered at 1350 and 1250 °C, respectively. Domain wall relaxation frequency, f_r, and Néel temperature, T_N, are found to increase with Mg substitution. It is observed that when Zn is completely substituted by Mg in Ni_0.50Zn_0.50-xMg_xFe₂O₄, the T_N is increased by 106% and f_r by 178%. On the other hand, μ_i^′ decreases by 86%. It is observed that all samples are in ferrimagnetic state at room temperature. The number of Bohr magneton, n(μ_B), decreases with increasing Mg substitution which is explained by probable cation distribution in the spinel crystal structure. Possible explanation for the observed features of microstructure, initial permeability, DC magnetization and Néel temperature of the studied samples are discussed.