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.

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.

Ferrite samples with composition, Cd_𝑥Co_1−𝑥Fe₂O₄ (𝑥 = 0.80, 0.85, 0.90, 0.95 and 1.0), were prepared by standard ceramic method and characterized by XRD, IR and SEM techniques. X-ray analysis confirms the formation of single phase cubic spinel structure. Lattice constant and grain size of the samples increase with increase in cadmium content. Bond length (A–O) and ionic radii (𝑟_A) on 𝐴-sites increase, whereas bond length (B–O) and ionic radii (𝑟_B) on 𝐵-site decrease. The crystallite sites of the samples lie in the range of 29.1–42.8 nm. IR study shows two absorption bands around 400 cm^-1 and 600 cm^-1 corresponding to tetrahedral and octahedral sites, respectively.