Tailored physical and magnetic properties by La 3+ dopants in Mg–Ni–Co nanoferrites: insight into the law of approach to saturation

In this study, lanthanum La-doped Mg 0.33 Ni 0.33 Co 0.33 Fe 2-x La x O 4 (0.00 ≤ x ≤ 0.08) nanoferrites were synthesized using the co-precipitation method. The physical properties of the samples were examined using X-ray diffraction (XRD), transmission electron microscope (TEM), selected area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and vibrating sample magnetometer (VSM). The XRD results confirmed the formation of a single-phase spinel ferrite. Upon increasing the La 3+ ions concentration, crystallite and particle sizes decreased as revealed from XRD and TEM analysis, respectively. The values of the lattice parameter estimated from the SAED are in harmony with those obtained from XRD patterns. The appearance of two bands in the FTIR spectra, mainly in the range of 592–595 and 387–422 cm −1 , confirms the formation of the spinel structure. Furthermore, the red shift in A 1g Raman mode, observed in La-doped nanoferrites, was attributed to the active motion of Fe 3+ towards the A sites. The samples demonstrated a ferromagnetic behavior with a reducing saturation magnetization from 31.87 to 12.99 emu/g as x increased from 0.00 to 0.08, respectively. Different forms of the law of approach to saturation (LAS) were employed to fit M–H hysteresis curves of experimental data. Moreover, different parameters were investigated, including the exchange field, anisotropy field, Bohr magneton, and magnetocrystalline anisotropy. These parameters were further analyzed to check the accuracy of the fitting and the best-suited model.