Study of the Structural, Magnetic and Electrical Properties of Nickel - Cadmium Ferrites

Abstract

This thesis describes the experimental investigation of the structural, magnetic and electrical properties of Nii.CdFe2O4 ferrites for 0.0 :5 x :!~ 0.8, prepared by conventional double sintering ceramic method. The characterization of the samples has been performed by X-ray diffraction. Magnetic properties have been measured as a function of field, temperature and frequency, using vibrating sample magnetometer, SQUID magnetometer and Impedance Analyzer. X-ray diffraction results confirmed the single-phase spinel structures of all the studied ferrite samples. The lattice parameter increases linearly with increasing Cd concentration obeying Vegard's law. This is attributed to the replacement of smaller Fe ions (0.64A) from A-sites to B-sites by larger Cd2 ions (0.97 A). The bulk density of the samples increases monotonically with increasing Cd content signifying that Cd has a pronounced effect on the densification of the ferrites. Curie temperature decreases linearly with increasing Cd content which has been explained due to the weakening of A-B exchange interaction. Saturation magnetization at 20K increases with Cd content up to x = 0.5 and decreases thereafter. Ned's two sublattice collinear model is applied for the initial rise of the magnetization up to x :!~ 0.5 and beyond that three sublattice non-collinear model proposed by Yafet- Kittel are predominant. This suggests the existence of canted spin structure in the ferrite system with higher content of Cd. The sample with x = 0.8 shows anomalous temperature dependent magnetic ordering on applied magnetic field. Low field (5 Oe) magnetization shows antiferromagnelic ordering at 39K while the ferromagnetic ordering with T = 172K is dominant with the application of high field (1 T). This implies that the magnetic ordering in this sample is dependent on magnetic field. Permeability increases with increasing Cd concentration as well as increasing sintering temperature for all the studied samples. The increase of permeability is ascribed to the increase of density and grain size. For the sample with x=0.6, the permeability decreases with increasing sintering temperature in spite of high density which may be attributed to the intragranular porosity that inhibits easy domain wall mobility resulting in a decrease of permeability. Room temperature DC resistivity decreases with Cd content and sintering temperature.