Influence of Gd3+ ion doping on structural, optical, and magnetic properties of (Mg-Ni-Co) nanoferrites

The characterization of (Mg-Ni-Co) nanoferrites doped with small different concentrations of gadolinium rare earth metal (Gd3+), prepared by the chemical co-precipitation method, is reported in this study. The XRD results reveal that the crystallite sizes, which are close to the particle size detected from TEM analysis, decrease upon adding Gd3+. Furthermore, the lattice constant a increases from 8.351 to 8.367 angstrom as the Gd3+ concentration (x) increases from 0.00 to 0.08. HRTEM images reveal the presence of different grains with different lattice plane orientations. Furthermore, the appearance of concentric circles in the SAED patterns verified the samples' polycrystalline nature. The presence of the active modes of the spinel structure was confirmed by the Raman analysis with a slight shift upon increasing the Gd3+ concentrations. Moreover, the photoluminescence (PL) analysis revealed the presence of a sharp peak in the UV region and structural defects in the prepared samples. Mossbauer spectroscopy and vibrating sample magnetometer (VSM) were used to examine the magnetic properties of the prepared samples. From the Mossbauer analysis, it was suggested that Gd3+ ions occupy the octahedral site. In addition, the saturation magnetization (M-s) and magnetocrystalline anisotropy (K) decreased from 31.87 to 15.76 emu/g and from 0.0057 to 0.0014 J/m(3) with the increase of Gd3+ concentration from 0.00 to 0.08, respectively. Finally, different forms of the law of approach to saturation (LAS) for ferromagnetic materials were used for the fitting of M-H hysteresis loops at high applied fields. The obtained results show that the LAS model, mainly M = M-s (1- b/H-2) + H-x, can effectively describe the doping of Gd3+ for all concentrations. This model exhibits well-fitting with high R-2 values and provides relevant values of the magnetic parameters.