Investigation on structure, thermodynamic and multifunctional properties of Ni-Zn-Co ferrite for Gd³⁺ substitution

This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni-Zn-Co ferrite tailored by Gd³⁺ substitution at the B-site replacing Fe³⁺ ions. The synthesized composition of Ni_0.7Zn_0.2Co_0.1Fe_2- Gd O₄ (0 ≤ x ≤ 0.12) crystallized with a single-phase cubic spinel structure that belongs to the Fd3̄m space group. The average particle size decreases due to Gd³⁺ substitution at Fe³⁺. Raman and IR spectroscopy studies illustrate phase purity, lattice dynamics with cation disorders and thermodynamic conditions inside the studied samples at room temperature (RT = 300 K). Ferromagnetic to paramagnetic phase transition was observed in all samples where Curie temperature (T _C) decreases from 731 to 711 K for Gd³⁺ substitution in Ni-Zn-Co ferrite. In addition, Gd³⁺ substitution reinforces to decrease the A-B exchange interaction. Temperature-dependent DC electrical resistivity (ρ _DC) and temperature coefficient of resistance (TCR) have been surveyed with the variation of the grain size. The frequency-dependent dielectric properties and electric modulus at RT for all samples were observed from 20 Hz to 100 MHz and the conduction relaxation processes were found to spread over an extensive range of frequencies with the increase in the amount of Gd³⁺ in the Ni-Zn-Co ferrite. The RLC behavior separates the zone of frequencies ranging from resistive to capacitive regions in all the studied samples. Finally, the matching impedance (Z/η ₀) for all samples was evaluated over an extensive range of frequencies for the possible miniaturizing application.