Effect of Al3+-substitution on the electrical and magnetic properties of Ni1.05Sn0.05Fe1.9O4 ferrites

The effect of Al3+-substitution on d.c. resistivity, dielectric constant, initial permeability, saturation magnetization and Curie temperature has been studied for Ni1.05Sn0.05AlxFe1.9-xO4 ferrites, wherein x varies from 0 to 0.5 in steps of 0.1. The d.c. resistivity increases slowly for x less than or equal to 0.3 followed by a rapid increase for x > 0.3. The variation is explained on the basis of Verwey hopping as well as polaron hopping mechanisms, and the dilution effect of Al3+ ions. The behaviour of dielectric constant is attributed to interfacial polarization and follows the Koops model. The saturation magnetization and the Curie temperature decrease continuously with increasing Al3+ content and are explained using the concepts of sublattice magnetization and exchange interactions. The decrease in initial permeability is attributed primarily to decrease in saturation magnetization. The dispersions in initial permeability and magnetic loss tangent are also discussed.