Impact of palladium ions doping on structural, magnetic, and electromagnetic properties and hyperfine interactions of Co-Ni nanospinel ferrites

Pd²⁺ ions substituted Co-Ni spinel ferrites nanoparticles (Co_0.5Ni_0.5Pd_xFe_2−xO₄ (Pd→CoNiFe₂O₄) NSFs) have been synthesized via a hydrothermal route assisted with polyethylene glycol (PEG). XRD, SEM, TEM, HR-TEM, VSM, and Mossbauer spectroscopy were used to provide a thorough analysis of the phase and structure, magnetic characteristics, and hyperfine interactions. Magnetic features of prepared NPs showed ferrimagnetic behavior. In comparison to non-doped NPs, the incorporation of a small amount of Pd ions within Co_0.5Ni_0.5Fe₂O₄ provoked initially a slight rise in magnetization and coercivity magnitudes. Furthermore, as the Pd²⁺ ions content continued to increase, magnetization and coercivity exhibited a diminishing trend. These observations are explained by changes in size and morphology, variations in the strength of superexchange interactions, and cation redistribution. Mössbauer spectra for all samples exhibited four distinct magnetic sextets. The doped ions were substituted with Fe³⁺ ions at B site. The cation distribution was ascertained through the utilization of Mossbauer spectroscopy. An investigation of electromagnetic (EM) properties was conducted within 2–18 GHz. EM characteristics of the samples can be explained by the main contribution in EM absorption from the electric energy losses.