Nano sized single phase cubic spinel systems with the general formula Mn0.2Ni0.
6 Zn0.2 Gdx Fe2-xO4 (x=0, 0.02, 0.
04, 0.06) with enhanced structural and magnetic properties have been synthesized successfully by the sol-gel preparation technique. Doping with Gd3+ which replaces Fe3+ ions at octahedral site inhibits grain growth and decreases the grain size. The increase in lattice parameter, which indicates the expansion of unit cell of the prepared samples, is due to the presence of larger Gd3+ ions in place of Fe3+ ions.
SEM and HRTEM images show that the samples are spherical in shape and slightly agglomerated. Frequency dependence of dielectric constant shows normal ferrite behaviour and agrees well with Koop’s theory. Thermal enhancement of drift mobility of charge carriers leads to the increase in dielectric constant with temperature. The linear rise in AC conductivity with frequency of applied field indicates small polaron hopping mechanism. The dilution of the net magnetization by the non magnetic Gd ions results in decrease in saturation magnetization.
The decline in magneto crystalline anisotropy decreases the coercive force field. The saturation magnetization and coercivity of the samples increase by lowering the temperature. A strong deviation from the collinear ferrimagnetism has been noted due to spin canting.
Y-K angle increases with Gd substitution in Mn substituted Ni-Zn mixed ferrite systems. Higher Y-K angles obtained make them promising materials for use in magnetoresistive (MR) applications.
