Mechanical behavior, enhanced dc resistivity, energy band gap and high temperature magnetic properties of Y-substituted Mg–Zn ferrites

We report the synthesis of Y-substituted Mg–Zn [Mg_0.5Zn_0.5Y_xFe_2−xO₄ (0 ≤ x ≤ 0.05)] ferrites using conventional standard ceramic technique. The samples were characterized by x-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM), FTIR spectroscopy, UV–Vis spectroscopy and quantum design physical properties measurement system (PPMS). XRD patterns confirm the single phase cubic spinel structure up to x = 0.03 and appearance of a secondary phase of YFeO₃ for higher Y contents. FESEM images depict the distribution of grains and EDS spectra confirmed the absence of any unwanted element. Completion of solid state reaction and formation of spinel structure has been revealed from FTIR spectra. The FTIR data along with lattice constant, bulk density and porosity were further used to calculate the stiffness constant (C _ij), elastic constant and Debye temperatures. Mechanical stability of all studied compositions is confirmed from C _ij using Born stability conditions. Brittleness and isotropic nature are also confirmed using Poisson's ratio and anisotropy constants, respectively. The enhancement of dc electrical resistivity (10⁵Ω cm to 10⁶Ω cm) with Y content is observed. The energy band gap (increased with Y contents) is found in good agreement with dc electrical resistivity. Ferrimagnetic to paramagnetic phase change has been observed from the field dependent high temperature magnetization curves. The magnetic moments and saturation magnetization were found to be decreased with increasing temperature. The Curie temperature (T_c) has been measured from temperature dependent magnetic moment (M-T) and initial permeability (μ′_i-T) measurements and found to be in good agreement with each other. Decrease in T_c with Y content is due to redistribution of cations and weakening of the exchange coupling constant. The magnetic phase transition has been analyzed by Arrott plot and found to have second order phase transition. The dc resistivity endorses the prepared ferrites are suitable for high frequency and high temperature magnetic device applications as well. (paper)