Study of magnetic properties of LixMg0.4Ni0.6-2xFe2+xO4 ferrites

Abstract

A series of polycrystalline spinel type ferrites with the nominal composition LixMg0.4Ni0.6-2xFe2+xO4, where x = 0.0 to 0.3 in steps of 0.05, has been investigated thoroughly. The samples are fabricated using conventional solid state reaction technique. Pellet and toroid shaped samples are prepared from each composition and sintered at temperatures of 1050, 1100,1150 and 1200˚C in air for 6 hours. Structural and surface morphology are studied by x-ray diffraction technique and high resolution optical microscopy, respectively. The AC magnetic properties of these ferrites are characterized by high frequency (300 kHz-110 MHz) complex permeability measurements. DC magnetizations of all samples are measured by Vibrating Sample Magnetometer (VSM). The influence of microstructure, various cation substitution and sintering temperatures on the complex permeability of above mentioned ferrites are discussed. A possible correlation among sintering temperature, average grain size and density is also discussed. It is noticeable that X-ray diffraction patterns of all samples show the formation of spinel crystal structure. Lattice parameters are calculated using the Nelson Riley function. The lattice constants increase linearly with the increase of Li content, obeying Vegard s law. 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 on the average grain size. In LixMg0.4Ni0.6-2xFe2+xO4 ferrites the real part of initial permeability, / i  and saturation magnetization, Ms, increase with the increase of Li content up to x= 0.25 and beyond x= 0.25, both / i  and Ms decrease. The decrease of / i  and Ms beyond x= 0.25 indicate the possibility of noncollinear spin canting effect. It is also found that / i  increases with increasing average grain size of the samples. It is also observed that / i  increases with sintering temperatures for all ferrites because high sintering temperature performs uniform grain growth. Highest value of / i  and Q-factor is observed for various LixMg0.4Ni0.6-2xFe2+xO4 ferrites sintered at 1100˚C and among these, highest / i  ( / i = 66 ) and maximum Q-factor ( Q value=4653) is found for Li0.25Mg0.40Ni0.10Fe2.25O4, ferrite. From DC magnetization data it is found that Li0.25Mg0.40Ni0.10Fe2.25O4 ferrite has maximum saturation magnetization value among LixMg0.4Ni0.6-2xFe2+xO4 ferrites.