Structural, morphological and magnetic properties of (Ni_0.5Co_0.5)[Ga_xGd_xFe_2–2x]O₄ nanoparticles prepared via sonochemical approach

The impact of Ga³⁺ and Gd³⁺ co-substitution on different types of behavior of Ni–Co nanospinel ferrites (NSFs), (Ni_0.5Co_0.5)[Ga_xGd_xFe_2–2x]O₄ (0.000 ≤ x ≤ 0.025), was investigated. NSFs were fabricated through ultrasound irradiation. The structure, composition, and spherical morphology of all products were verified by numerous characterization techniques such as X-ray diffraction (XRD), scanning and transmission electron microscopes (SEM and TEM), and selected area electron diffraction (SAED). Mossbauer spectra are composed of two ferromagnetic sextets and one paramagnetic doublet. These spectra were fitted to extract hyperfine parameters of the doped samples. Both sublattices' hyperfine magnetic field decreases with substitution. The isomer shift values show that the Mossbauer spectra are composed of magnetic Fe³⁺ sextets. The magnetization measurements at variable magnetic field (M-H) were investigated via a vibrating sample magnetometer (VSM) at temperatures (T) from 300 to 10 K. All NSFs disclose ferrimagnetic behavior at both 300 and 10 K at which they are soft and hard, respectively. We determined that the remanence magnetization (M_r), saturation magnetization (M_s), and magneton number (n_B) decrease with increasing Ga³⁺ and Gd³⁺ ions contents. The reduction in these values is predominantly recognized to be the impact of cation redistribution and surface spins on tetrahedral (T_d) and octahedral (O_h) sites. As the Ga³⁺ and Gd³⁺ contents increase, the coercivity (H_c) is also found to decrease.