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Nanocrystalline Co-substituted Ni–Zn ferrites have been synthesized by employing a co-precipitation technique using oxalate precursors. The co-precipitated oxalates were decomposed in air at 650 °C for 1 h and the powder was sintered at 1000 °C. The phase formation of the sintered ferrite was confirmed by x-ray diffraction studies. The lattice parameter a (Å) increases with the addition of Co2+ which is attributed to the large ionic size of Co2+ (0.78 Å), which replaces Ni2+ (0.74 Å). The crystallite size has been estimated by the Debye–Scherrer formula using the full width at half-maximum (FWHM) of the line broadening of the (311) reflection and it is found to be in the range of 25–28 nm. Also, with increasing cobalt content the magnetocrystalline anisotropy constant (K1) and magnetostriction constant (λs) increase, and the grain size decreases, hence the value of initial permeability μi decreases. The saturation magnetization Ms and magnetic moment (nB) do not show any significant variation for all compositions varying with the cobalt content.

The ferrite material with compositions Ni 0.7 Cu 0.1 Zn 0.2 La x Fe 2−x O 4 (where x = 0, 0.015, 0.025, and 0.035) was synthesized by oxalate co-precipitation method. The ferrite samples were characterized by thermo-gravimetric and differential temperature analysis (TG-DTA), energy-dispersive X-ray analysis (EDAX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM) techniques. The EDAX analysis confirmed the formation of required stoichiometric ferrite samples. The formation of cubic spinel structure with the presence of weak ortho-ferrite phases was confirmed from X-ray diffraction analysis. The lattice constant of all the ferrites was found to be increase with increase in La 3+ content. The presence of main two recognized strong absorption bands in the frequency range 400-600 cm −1 in the FTIR spectra shows the formation of well spinel ferrite. Morphological study shows that grain size of the ferrites lies in the range 16.23-24.21 nm. It is observed that the saturation magnetization and magnetic moment of Ni-Cu-Zn ferrites decrease with La 3+ content.