Comparative study of the effects of rare earth ions in a high frequency Ni-Zn ferrite

Some effects of the rare-earth ions on the properties of the polycrystalline stoichiometric ferrite with formula Ni-0 7Zn0.3Fe1.98R0.02O4(R=Yb, Er, Dy, Tb, Gd, Sm and Cc) are described. The results obtained reveal that by introducing a relatively small amount of R2O3 instead of Fe2O3, an important modification of both structure and properties can be obtained. R2O3 facilitates the formation of the crystalline secondary phases (orthoferrite, garnet) on the grain boundary which inhibit the ferrite grain growth. The R ions tend to flatten the mu(i)-T curve, shift the Curie point to lower temperature and increase the electrical resistivity. The variation of these properties with the R species has been explained as an effect of the ionic radius size which varies from 0.86 for Yb to 1.07 for Ce.