Comparative Study of the Effects of Rare Earth Ions in a High Frequency Ni-Zn Ferrite

Abstract
Some effects of the rare-earth ions on the properties of the polycrystalline stoichiometric ferrite with formula Ni_0.7Zn_0.3Fe_1.98R_0.02O₄(R=Yb, Er, Dy, Tb, Gd, Sm and Ce) 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 µ_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.