Magnetic properties of cadmium substituted lithium ferrites

Ferrites are a class of important ferromagnetic oxide materials with spinel structure having excellent soft magnetic properties in electromagnetic devices such as inductors, converters or electromagnetic wave absorbers, phase-shifters, radar, etc. in the radio frequency range. In this paper, polycrystalline Li-Cd ferrites with the general formula Li0.5-x/2CdxBi0.02Fe2.48-x/2O4 for x = 0.0-0.7 were prepared by conventional double sintering ceramic technique and their magnetic properties were measured. Single-phase cubic structure is confirmed by X-ray diffractometer. This result demonstrates that the prepared samples are homogeneous and the sharp peaks reveal that the samples are in good crystalline form. Curie temperature has been taken as the temperature at which a sharp fall of permeability is observed which corresponds to the complete spin disorder. From Curie temperature measurement, a linear dependence of the Curie temperature is observed for the substitution of Cd2+ for Li1+ which occurs due to the weakening of A-B exchange interaction. The sample with x = 0.7 shows anomalous temperature dependent magnetic ordering as it is paramagnetic at room temperature. The magnetic moment (nB) and saturation magnetization (Ms) are found to increase with cadmium upto x = 0.3 and then tend to decrease for x > 0.3. The increase in magnetic moment with cadmium is attributed to Neel's two sublattice model according to which the magnetic moment is the vector sum of lattice magnetic moment. The decrease in magnetization for x > 0.3 obeys Yafet-Kittel (Y-K) model. The increase in Y-K angles for x > 0.3 indicates the increased favor for triangular spin arrangements on B-sites. This suggests the existence of canted spin structure in the ferrite system with higher content of Cd.