Structural and magnetic properties of nanocrystalline LixCu0.1Co0.1Zn0.8-2xFe2+xO4 prepared by auto combustion technique

Abstract

Nanocrystalline LixCu0.1Co0.1Zn0.8-2xFe2+xO4 with x= 0.00, 0.10, 0.20, 0.30 and 0.40 have been synthesized by autocombustion technique. The particle sizes of various LixCu0.1Co0.1Zn0.8-2xFe2+xO4 are found to be in between 24 and 46 nm. Pellet and toroid shaped samples are prepared from the ferrite powder and are sintered at 1100, 1150, 1200, 1250 and 1300 ºC in air for 1 hour. Structure and surface morphology are studied by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) respectively. The magnetic properties of these ferrites are characterized with a high frequency (100 kHz-120 MHz) Impedance Analyzer. The temperature dependence of initial permeability is also studied for getting Neel temperature, TN. The influence of microstructure and sintering temperature on the complex permeability of these samples are discussed. XRD patterns show the formation of single phase spinel crystal structure. Lattice parameters are calculated using Nelson Riley function. There is a compression of unit cell dimension depending on Lithium (Li) substitutions in these compositions. 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. The real part of initial permeability, / i ,increases with increasing Li+ content up to x=0.10 and beyond x = 0.10, / i decreases in LixCu0.1Co0.1Zn0.8-2xFe2+xO4 for a fixed sintering temperature. / i  increases with increasing sintering temperature up to 1150 ºC and above this temperature / i  starts to decrease for a particular composition. The / i remains fairly constant in the frequency range up to some critical frequency, called resonance frequency (fr). The high natural resonance frequency (44.8 MHz) is found for Li0.2 Cu0.1Co0.1Zn0.4Fe2.2O4. A sharp decrease in / i  and increase in // i  above the fr is noticed for x=0.10 and x=0.20. The relative quality factor (1486) is found to maximum for Li0.1 Cu0.1Co0.1Zn0.6Fe2.1O4 sintered at 1150 ºC.