Development of lithium ferrite based ceramics for microwave applications

Abstract

Spinel ferrites have gained attention for a long period of time due to their unique electrical, optical, and magnetic properties. They are also very promising for applications such as circulators, phase shifters, memory, magnetic recording devices, gas sensing, etc. The present thesis is focused on the synthesis of lithium ferrite-based ceramics and thin films. Lithium ferrite exhibits high Curie temperature, square hysteresis loop, high saturation magnetization, excellent dielectric properties, high resistivity, etc. The solid-state reaction method is used to prepare substituted lithium ferrites and composites. The effect of alkaline earth elements such as Sr and Mg on the structural, microstructural, dielectric (1 MHz 1 GHz), and magnetic response is analyzed. Enhanced dielectric response (and#949;r = 3034, tanand#948; = 0.001 at RT, 1 MHz) is observed for the Mg composition, x = 0.005, whereas in the case of Sr series, the best dielectric response is observed for x = 0.003 (and#949;r = 5986 and tanand#948; = 1.17 at RT, 1 MHz). The obtained EA for LMFO and LSFO is 1.39 0.35 eV and 0.124 0.077 eV, respectively. The LMFO with x = 0.007 exhibited the best permeability (and#956;r = 29) and magnetic properties (Ms = 55 emu/g) at room temperature. Also, in the LSFO series, x = 0.007 showed the highest magnetization among all samples (MS = 61 emu/g). Improved dielectric response with low magnetic as well as dielectric loss is observed for Mg substituted lithium ferrite as compared to Sr. The combined magnetic, dielectric, and permeability response made the Mg substituted lithium ferrite more suitable for circulators and phase shifters. Again, the lithium ferrite/carbon black and Dy substituted lithium ferrite/carbon black composites are prepared, and EMI shielding effectiveness is analyzed in the X (8.2 12.4 GHz) and Ku (12.4 18 GHz) frequency bands. Permittivity and permeability are also analyzed. Shielding effectiveness is enhanced with the carbon black as well as Dy content. The maximum shielding effectiveness of 24 dB was obtained for LD