Effect of copper substitution on the magnetic properties of Fe2.5Zn0.5-xCuxO4

Abstract

Polycrystalline Fe2.5Zn0.5-xCuxO4 ferrites with x= 0.00-0.45 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. Samples prepared from each composition are sintered at various temperatures (1050-1150C) and structural and surface morphology are studied by X-ray diffraction (XRD). The magnetic properties of these ferrites are characterized with high frequency (100 kHz-120 MHz) Impedance Analyzer. The influence of microstructure, various cation distribution and sintering temperature on the complex initial permeability of these samples are discussed. X-ray diffraction pattern show the formation of spinel structure. Lattice parameters are calculated using the Nelson -Riley function. It is also found that the lattice constant decreases with increasing Cu content, obeying Vegard‘s law due to smaller ionic radius (0.65Å) of Cu2+ compared to Zn2+ (0.74Å ). This result is explained with the help of ionic radii of substituted cations. The microstructural study shows that both sintering temperatures and cations substitutions have great influence. As the sintering temperature increases, the bulk density increases (depending on compositions), and hence the porosity decreases for all compositions. The initial permeability increases at a certain composition (up to x=0.30) beyond that decreasing. It is also observed that the real part of initial permeability increases with sintering temperatures for all ferrites because high sintering temperature helps to develop uniform grain. The real part of the initial permeability ( / i ) remains fairly constant in the frequency range up to some critical frequency which is called resonance frequency. The highest / i for each sample has been observed sintered at 1150 ºC because the microstructure is homogeneous with a uniform size distribution.The loss factor increases with increasing of Cu content and sintering temperature. The relative quality factor Q both increases with increasing sintered temperature and Cu content up to x=0.30 then decreasing. For inductors used in filter applications, the quality factor is often used as a measure of performance. It is observed that the sample sintered at 1150ºC is of the highest Q value (3688) for Fe2.5Zn0.20Cu0.30O4 samples.