Bi³⁺ and V³⁺ co-substituted Ni-Co spinel ferrites: Synthesis, optical, magnetic characterization and hyperfine interaction

Ni_0.5Co_0.5V_xBi_xFe_2-2xO₄ spinel ferrite nanoparticles with composition (x = 0.00, 0.02, 0.04, 0.06 and 0.08) (CoNiVBiFeO (x = 0.00–0.08) SFNPs) were well fabricated hydrothermally. The consequence of co-substitution of both Bi³⁺ and V³⁺ ions on structure, morphology, and magnetic features of Ni_0.5Co_0.5Fe₂O₄ SFNPs were studied using XRD (X-ray diffractometry), scanning (SEM) and transmission (TEM) electron microscopies along with EDX, XPS (X-ray photoelectron spectroscopy), VSM (vibrating sample magnetometry) and Mossbauer spectroscopic techniques. The pure spinel ferrite (SFs) phase was approved via XRD. The morphology of SFNPs were revealed by SEM and TEM. Hyperfine parameters are determined from fitting room temperature Mössbauer spectra. The V³⁺ and Bi³⁺ ions occupy mainly at B site. The isomer shift values are coupled with the characteristics of the high spin Fe³⁺ ion. The influence of V³⁺ and Bi³⁺ ions co-doping on the magnetic features of Ni-Co SFNPs has been also investigated at 300 and 10 K. The saturation magnetization (M_s), remanence (M_r), coercive field (H_c), and Bohr magneton number (n_B) are extracted from the recorded M-H hysteresis loops. Nanomagnetic materials with x content of 0.02, 0.08, and 0.10 exhibited superparamagnetic (SPM) behavior, whereas other products with x content of 0.00, 0.04, and 0.06 displayed soft ferrimagnetic behavior at ambient temperature. The different prepared nanoferrites displayed hard ferrimagnetic characteristic at 10 K. The M_s and M_r values are decreased as result of V³⁺ and Bi³⁺ ions co-doping. However, H_c does not show a monotonic trend. The fluctuations in magnetic moments of ions, super-exchange coupling, and distribution of cations are correlated with the changes in magnetic parameters to explain their variations.