Influence of Gd³⁺-substitution on structural, magnetic, dielectric and modulus spectroscopic characteristics of ZnFe₂O₄ spinel ferrite nanoparticles

The gadolinium (Gd³⁺) substituted zinc ferrite nanoparticles (ZnFe_2−xGd_xO₄) for Gd³⁺ (x = 0.00, 0.05, 0.10, 0.20) have been synthesized by honey mediated sol–gel auto-combustion method. The X-ray diffraction study revealed the formation of spinel ferrite crystal structure. The Raman spectroscopy and Fourier transform infrared spectroscopy study well support the XRD results analysis. The field emission scanning electron microscopy micrograph revealed spherical morphology and grain size around 10–30 nm for ZnFe_2−xGd_xO₄ (x = 0.10) nanoparticles. The presence of Zn²⁺ and Fe³⁺ oxidation state in synthesized nanoparticles was confirmed by X-ray photoelectron spectroscopy. Magnetic properties of the Gd³⁺ substituted zinc ferrite nanoparticles were investigated by vibrating sample magnetometer at room temperature. The conversion of magnetic hysteresis curves from ferromagnetic to a paramagnetic with the substitution of Gd³⁺ in zinc ferrite nanoparticles was observed. Frequency dependent dielectric constant and ac conductivity measurements revealed that Gd³⁺ substitution improved the value of dielectric constant and ac conductivity of the Gd³⁺ substituted zinc ferrite nanoparticles. Further, the existence of two semicircles in Cole–Cole plot demonstrated the role of both grains and grain boundaries to conduction process in synthesized Gd³⁺ ion substituted zinc ferrite nanoparticles. Furthermore, the grain relaxation time (τ_g), grain boundary relaxation time (τ_gb), grain resistance (R_g), grain capacitance (C_g), grain boundary resistance (R_gb) and grain boundary capacitance (C_gb) for synthesized ZnFe_2−xGd_xO₄ (x = 0.00, 0.05, 0.10, 0.20) nanoparticles have been calculated using modulus spectroscopy analysis.