Polycrystalline ferrites, Zn_xMg_1−xFe_2−yNd_yO₄ (x = 0.00, 0.20, 0.40, 0.60, 0.80 and 1.00;y = 0.00, 0.05 and 0.10) were prepared by standard ceramic method. X-ray diffraction study of these compositions revealed the formation of single phase spinels. Seebeck coefficient was obtained from thermo emf measurement by keeping constant temperature difference of 10 K across the pellet. The values of Seebeck coefficient were found to be negative showing majority charge carriers ofn-type, suggesting the mechanism of conduction to be predominantly by electron hopping. The substitution of Nd₃₊ ion, which perhaps resides at the B-site, resulting in a decrease in the Seebeck coefficient. This decrease was assigned to the decrease of population of Fe₃₊ ion at the B-site. The activation energies calculated both from mobility plots and from dc resistivity plots were found comparable. The Fermi energy,E_F(0), which was estimated by intrapolation ofE_F-T curves toT = 0 K, was found less than the activation energy. This difference was attributed to electron hopping energy.

Compositions of polycrystalline Zn_𝑥Mg_1-𝑥Fe_2–𝑦Nd_𝑦O₄ (𝑥 = 0.00, 0.20, 0.40, 0.60, 0.80 and 1.00; 𝑦 = 0.00, 0.05 and 0.10) ferrites were prepared by standard ceramic method and characterized by X-ray diffraction, scanning electron microscopy and infrared absorption spectroscopy. Far infrared absorption spectra show two significant absorption bands, first at about 600 cm^–1 and second at about 425 cm^–1 , which were respectively attributed to tetrahedral (A) and octahedral (B) sites of the spinel. The positions of bands are found to be composition dependent. The force constants, $K_T$ and $K_O$, were calculated and plotted against zinc concentration. Compositional dependence of force constants is explained on the basis of cation–oxygen bond distances of respective sites and cation distribution.

Polycrystalline soft ferrites, Zn$_x$ Cu$_{1–x}$ Fe₂O₄ (𝑥 = 0.30, 0.50, 0.70, 0.80 and 0.90), doped with controlled amount of calcium chloride (CaCl₂) were prepared by standard ceramic route and studied for a.c. susceptibility. X-ray diffraction studies of the compositions reveal formation of single-phase cubic spinel. The values of lattice constant increase as doping percentage of CaCl₂ increased from 0.01% to 0.05% and afterwards decrease slightly. The presence of chlorine ions is confirmed by absorption peak in far IR spectra near 650 cm^-1 for all the samples. The variation of a.c. susceptibility with temperature shows the existence of single domain structure for 𝑥 = 0.3 and exhibits transition from single domain to multidomain structure with increased Ca²⁺ contents from 0.01 to 0.1%. The composition, 𝑥 = 0.5, shows multidomain structure independent of Ca²⁺ content. The samples for 𝑥 = 0.70, 0.80 and 0.90 show paramagnetic behaviour at and above room temperature.