Effect of divalent cation substitution (M = Mn, Ni, Mg, Cu) on the structural, magnetic and electrical properties of MFe2O4 spinel ferrites

Abstract

In This study, a systematic investigation of the influence of the nature of the divalent cation (M²⁺ = Ni, Mg, Cu, Mn) on the multifunctional properties of spinel ferrites MFe₂O₄ synthesized by solid-state reaction is presented. X-ray diffraction (XRD) analyses validate the formation of single-phase cubic phases (space group Fdm). Despite significant disparities between the ionic radii of the M²⁺ cations (0.69 to 0.80 Å), the lattice retains its integrity, highlighting the high structural robustness of these materials in the face of cationic substitution. The precise determination of the oxidation states and the distribution of metal ions between the tetrahedral and octahedral sites of our prepared samples is carried out by X-ray photoelectron spectroscopy (XPS), while Raman spectroscopy corroborates these results by identifying the five vibrational modes characteristic of the spinel structure. Magnetic characterizations reveals that the ferrites MnFe₂O₄ and NiFe₂O₄ exhibit the highest saturation magnetizations (M_s), whereas MgFe₂O₄ shows a reduced magnetization due to the non-magnetic nature of the Mg²⁺ ion. The compound CuFe₂O₄ exhibits intermediate values, influenced by Jahn–Teller distortions and the mixed valence states of copper. The coercivity (H_c) varies depending on the cation, classifying some samples as soft magnetic materials, optimal for low-energy-loss applications. Furthermore, high-frequency analyses demonstrate that substitution engineering allows these ferrites to be optimized for microwave devices. Finally, electrical measurements performed between 400 and 700 K reveal remarkable performance for thermal sensing. Combined with an excellent stability factor, these properties authenticate the reliability of these materials for high-temperature sensor applications.