Electrical dynamics and Havriliak-Negami dielectric relaxation behavior of FeNi2O4 electromagnetic spinel nickelate

This work investigates the structural, dielectric, and magnetic properties of FeNi 2 O 4 , a cubic face centered normal spinel synthesized via sol-gel auto-combustion. X-ray diffraction and Rietveld refinement confirm its phase-pure Fd 3 ‾ m symmetry, with Fe and Ni cations occupying tetrahedral and octahedral sites, respectively. Impedance spectroscopy ( 40 Hz − 3.2 MHz , 453 − 673 K ) reveals grain boundary-dominated conduction and a negative temperature coefficient of resistance (NTCR), indicative of thermally activated polaron hopping. Nyquist plots suggest an equivalent circuit model R g ||Q g + R gb ||Q gb emphasizing the contributions of resistive interface and conductive bulk. Dielectric analysis demonstrates non-Debye relaxation governed by the Havriliak-Negami model, with dielectric permittivity dispersion attributed to Maxwell-Wagner polarization. Magnetic hysteresis measurements at room temperature confirm moderate ferrimagnetic behavior (Ms = 19 emu/g, Hc = 210 Oe), arising from Fe 3+ –Ni 2+ superexchange interactions. These results highlight FeNi 2 O 4 's dual functionality as a high-temperature dielectric and magnetically active material, offering insights for its integration into energy storage and spintronic systems.