Structural and initial permeability studies of nanocrystalline LixCu0.12Mn0.88-2xFe2+xO4 prepared by combustion technique

Abstract

The nanocrrystalline LixCu0.12Mn0.88-2xFe2+xO4 ferrites with x = 0.00, 0.10, 0.20, 0.30, 0.40 and 0.44 have been synthesized by combustion technique. The particle size of various LixCu0.12Mn0.88-2xFe2+xO4 is found to be 9 to 30 nm range. Disc- and toroid-shaped samples are prepared and sintered at various temperatures (1200, 1250, 1300 and 1350ºC) in air for 1 hour. Structural and surface morphology are studied by X- ray diffraction (XRD) and high resolution optical microscope, respectively. The magnetic properties of these compositions are characterized by high frequency (10 kHz-120MHz) complex permeability measurements. The influence of microstructure and sintering temperatures on the complex permeability of these ferrites are discussed. A possible correlation among sintering temperature, average grain size and density is also discussed. The XRD patterns of all samples clearly indicate the formation of single phase spinel structure. It is found that the lattice constant increases linearly with increasing Li contents obeying Vegard’s law. This is due to the fact that the ionic radius of Li+ (0.76Å) and Fe3+(0.645 Å) are greater than that of Mn2+ (0.67Å). The grain size increases with increasing Li content in LixCu0.12Mn0.88-2xFe2+xO4. The bulk density shows a decreasing trend with Li substitution. As the sintering temperature increases, bulk density increases, therefore porosity decreases for all samples. The real part of initial permeability, increases with increasing Li content in LixCu0.12Mn0.88-2xFe2+xO4. It is also observed that μi/ for each sample increases with sintering temperatures because of uniform grain growth. The remains fairly constant in the frequency range up to some critical frequency which is called resonance frequency, fr. It is also observed that higher the lower the fr of the material. This confirms with Snoek’s limit. The relative quality factor (Q) increases with increasing sintering temperature. Among all the studied samples, highest value of Q-factor (2165) is observed for x=0.40 sintered at 1300˚C.