Synthesis and study of microstructural analysis, magneto-optical properties, magnetocaloric and critical behaviors for the Ni_0.5Fe_0.5Cr₂O₄ spinel chromite

In this work, the microstructural, optical, magnetic, magnetocaloric, and critical behaviors for the Ni_0.5Fe_0.5Cr₂O₄ (abbreviated as NFCO) chromite spinel synthesized by sol–gel route were investigated. Rietveld refinement of the X-ray diagram shows that the compound was well crystallized in the cubic spinel structure (Fd3 ¯ m space group). The surface morphology of the sample was also examined by SEM analysis. The characteristic vibrational modes for the prepared sample were evaluated from the FTIR spectrum at room temperature. The behavior of the optical absorbance revealed that NFCO sample exhibits remarkable absorption of visible light with significantly lower band gap energy (E_gd = 1.74 eV). By comparing our results to those reported for the NiFe₂O₄ spinel, we show a drastic increase in coercivity, indicating the ability of Fe²⁺-substitution in improving the magnetic properties of nickel chromites for magnetic applications such as permanent magnets, permanent data storage tapes, and high-density magnetic recording. The magnetic transition from the ferrimagnetic (FiM) state to the paramagnetic (PM) state was observed from the M(T) curve at the Curie temperature (T_C = 90 K). The critical exponents were studied using the magnetic isotherms. The modified Arrott plots (MAP) and the critical isotherm show that both γ and δ exponents belong to an unconventional model; however, the β exponent shows small deviation from the mean-field model.