High Frequency Dielectric Behavior of Rare Earth Substituted Sr-M Hexaferrite

Strontium hexaferrites of a structural formula Sr1-xRExFe12O19, where RE=La3+, Nd3+ and Sm3+ with (x=0 to 0.30) were prepared by a standard ceramic technique. The lattice constants, density, porosity, dielectric constant and dielectric loss tangent were studied on a series of rare earth substituted strontium hexaferrites. The dielectric constant and dielectric loss tangent were measured in the frequency range of 0.3 GHz to 3.0 GHz at room temperature. The dielectric constant decreased with increasing frequency for all the three series. This behavior of dielectric properties with frequency has been explained with the Maxwell-Wagner type interfacial polarization in agreement with the Koops phenomenological theory. The substitution of rare earth ions into SrFe12O19 increases the value of the dielectric constant. This increase in dielectric constant could be due to the electronic exchange between Fe2+ ↔ Fe3+ and results in a local displacement determining the polarization of the ferrites. For these ferrite samples the Curie temperature decreases as rare earth ions substitution increases.