Ferromagnetic Properties of Zn substituted Spinel Ferrites for High Frequency Applications

This review focuses on two systems, nanocrystalline Zn substituted Co1-xZnxFe2O4 (0≤x≥1) and Ni0.4Zn0.2Mn0.4Fe2O4, were synthesized using microwave hydrothermal and auto-combustion method respectively. The synthesized powders were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), thermo-gravimetricdifferential thermal analysis (TG-DTA) and FTIR. The average particle size was obtained from TEM and it is found to be 17 nm. Zero field cooled (ZFC) and Field cooled (FC) measurements for Co1-xZnxFe2O4 reveal that samples with 0.6≤x≥1 have superparamagentic behavior at room temperature, which confirms weak interaction between magnetic particles. The blocking temperatures obtained form ZFC-FC curves decreases as Zn concentration increases. Lower reduced remnant magnetization (Mr/Ms) values (x<0.5) suggest that all the samples have uniaxial anisotropy. For Ni0.4Zn0.2Mn0.4Fe2O4 bulk densities of the samples were increased with an increase of sintering temperature. The grain sizes of all the samples vary in between 18 nm to 30 nm. The hysteresis loops show high saturation magnetization and low coercivity, indicates that it is a soft material. The incremental permeability (permeability with magnetic field superposition) was influenced by both ΔM and Hc. So these ferrites has the properties and are widely used as electromagnetic wave absorbing materials in the VHF/UHF region and as radar absorbing materials in C-band frequencies.