Effect of Zn substitution on structural and magnetic properties of nanocrystalline Li0.35-0.5xNi0.3ZnxFe2.35-0.5xo4

Abstract

Li-Ni-Zn ferrite nano-powders with nominal composition of Li0.35-0.5xNi0.3ZnxFe2.35-0.5xO4 (x = 0.00 - 0.40 in steps of 0.10) were synthesized by the chemical sol-gel auto combustion technique. Disk- and toroid-shaped samples prepared from each composition have been sintered at various temperatures (1100-1300°C) for 5h. The samples was characterized by X-ray diffraction (XRD), which has confirmed the formation of single phase spinel structure. The crystallite size of the as grown powder varied from 23 to 37 nm as measured using Scherrer formula. Surface morphology of the samples have been investigated using FESEM and elemental analysis of the compositions have been performed by EDX. The magnetic properties like complex initial permeability, loss factor, quality factor of these ferrites were measured from 100 Hz-120 MHz. The lattice parameters are calculated using the Nelson Riley function. Lattice constant increases with increase in Zn content, obeying vegard’s law. It is observed that the density, are found to increase with increasing sintering temperature up to 1250°C, then decreases. On the other hand, porosity have opposite trend. Average grain sizes of the samples are determined from FESEM micrographs by linear intercept technique. The Zn substitution acts as an accelerator of grain growth and uniform grain distribution in these compositions. The real part of permeability and saturation magnetization increase with increasing Zn content for a fixed sintering temperature. The maximum value of /  i (=254) is observed for Li0.15Ni0.3Zn0.4Fe2.15O4 sintered at 1250°C which is more than 6 times compared to that of parent composition. The loss factor (at 10 kHz) for this composition is also reduced 6 times. As a result high quality factor is observed in these compositions. The complex initial permeability has been explained with the help of microstructure, and the re-distribution of cations in the tetrahedral and octahedral sites. The weakening of exchange interaction may be confirmed by increasing the lattice parameter and decreasing Néel temperature (665 to 390°C) as the increase of Zn content. Substitution of Zn influences the magnetic properties due to modification of cation distribution.