Electrical and magnetic properties of rare earth substituted strontium hexaferrites

Samples of strontium ferrite (Sr-M) with different molar substitution concentrations of lanthanum, neodymium and samarium ions were prepared by a standard ceramic processing technique. AC conductivity, dielectric constant and dielectric loss tangent measurements were carried out in the frequency range of 20 Hz to 1MHz. The experimental results indicate that AC electrical conductivity increases with increasing frequency. The increase in AC conductivity with frequency can be explained on the basis of Koops model, whereas the dielectric constant and dielectric loss tangent variations have been explained with a Maxwell- Wagner type interfacial polarization in agreement with the Koops phenomenological theory. The effects of rare earth substitution on the magnetic properties such as the saturation magnetization moment (Ms), coercive field (Hc), remenance (Mr),and Curie temperature Tc (K) have been investigated. It is found that the values of the magnetization moment (Ms), and remenance (Mr) decrease with increasing rare earth ions substitution for all the series. The reason for the decrease may be both the magnetic dilution and spin canting, which promote reduction of superexchange interactions. The enhancement of Hc values may be due to higher magnetocrystalline anisotropy, where Fe2+ ion anisotropy on the 2a site could be dominant in all hexaferrites series