Effect of Mn substitution on the structural and magnetic properties of Fe2.5Zn0.5-xMnxO4

Abstract

Polycrystalline Fe2.5Zn0.5-xMnxO4 with x= 0.00-0.50 have been synthesized by the standard solid state reaction technique. Pellet- and toroid -shaped samples are prepared from the ferrite powders and sintered at various temperatures in air for 5 hours (1100-1250C). Structural and surface morphology are studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM). The magnetic properties of these ferrites are characterized with high frequency (10 kHz-120 MHz) using Impedance Analyzer. The influence of microstructure, various cation distribution and sintering temperature on the complex initial permeability of these samples are discussed. XRD pattern show the formation of spinel structure. Lattice parameters are calculated using the Nelson -Riley function. Lattice parameters are also analyzed by the Rietveld quantitative analysis. It is also found that the lattice constant increases with increasing Mn content, obeying Vegard’s law due to larger ionic radius (0.89Å) of Mn2+ compared to Zn2+ (0.74Å ). The micrograph shows that both sintering temperatures and cations substitutions have great influence on various properties. As the sintering temperature increases, the bulk density increases (depending on compositions), and hence the porosity decreases for all compositions. The initial permeability increases for substitution up to x=0.40 and beyond this slightly decrease. It is also observed that the real part of initial permeability ( / i ) increases with sintering temperatures because high sintering temperature helps to develop uniform grain. The / i remains fairly constant in the frequency range up to some critical frequency which is called resonance frequency. The highest / i has been observed sintered at 1250 ºC because of the homogenious microstructure with a uniform grain size distribution. The relative quality factor, Q, increases with increasing sintering temperature and Mn content up to x=0.40 then decreases for increasing the Mn content. The highest Q value (1013) is observed for Fe2.5Zn0.10Mn0.40O4 sintered at 1250ºC.