Structural, magnetic, dielectric and visible-light emission properties of Gd³⁺-doped Ni–Mg spinel ferrites for high-frequency and optoelectronic applications

Gd 3+ doped Ni-Mg ferrites with composition Ni 0.8 Mg 0.2 Gd x Fe 2-x O 4 (x = 0.00, 0.03, 0.05, 0.07, 0.09) were synthesized by the sol-gel auto-combustion process. XRD confirmed the formation of an FCC cubic spinel structure. The crystallite sizes ranged 34.93 – 29.46 nm. Surface morphology and elemental research were conducted FESEM and EDAX respectively, analysis revealed homogeneous morphology and elemental composition, with the average grain size increasing from 45.03 to 49.19 nm. FTIR spectra exhibited characteristic spinel bands at approximately 590 cm⁻¹ and 389 cm⁻¹, attributed to Fe–O stretching vibrations. UV–Visible spectroscopy revealed that band gap energy increases with Gd³⁺ doping due to lattice distortion and electronic structure modifications induced by Gd³⁺ incorporation and quantum confinement effects. The photoluminescence (PL) analysis indicated a distinct peak in the visible region, as well as the visible-light emission associated with near-band-edge radiative recombination. Dielectric measurements revealed frequency-dependent dispersion in the dielectric constant and dielectric loss tangent with changes in Gd³⁺ concentration. Magnetic measurements confirmed the soft ferromagnetic characteristics and the variation on magnetic interactions with Gd doping. The results demonstrate Gd³⁺ doping improves the properties of Ni–Mg spinel ferrites and enhances their potential for future high-frequency magnetic applications and optoelectronic applications.