Cr–Sc co-substituted nickel-cobalt nanospinel ferrites: An investigation of their structural, magnetic properties and hyperfine interactions

The chromium and scandium co-substituted nickel-cobalt nanospinel ferrites (NSFs) having general formula of Co_0.5Ni_0.5Sc_xCr_xFe_2-2xO₄ (CoNiScCr) (x ≤ 0.10) have been fabricated through the sol-gel route and citric acid as fuel and characterized by X-ray diffractometry (XRD), ⁵⁷Fe Mössbauer spectroscopy, vibrating sample magnetometry (VSM), and finally by scanning and transmission electron microscopy techniques (SEM and TEM, respectively). The crystallite size (D_max) values of the products were estimated to lay between 31 and 46 nm, which was calculated by the Scherrer formula. It was observed that the doping ions’ concentration did not have a linear impact on the expansion of the lattice constant. SEM and TEM present the cubic shape of CoNiScCr NSFs. All ratios demonstrate highly agglomerated cubic particles with diverse sizes. Both XRD and EDX (Energy Dispersive X-ray Spectroscopy) analyses confirmed the absence of any impurity/phases. Through an analysis of hysteresis loops at 300 (RT = room temperature) and 20 K, along with a probe of temperature-induced alteration in magnetization M, the magnetic properties of CoNiScCr (x ≤ 0.10) NSFs have been thoroughly investigated. Notably, all products exhibited complementary soft and hard magnetic behaviors at RT and 20 K, respectively. At 20 K, the observation of squareness ratio values surpassing 0.5 exhibits a single-domain behavior at this specific temperature. Magnetic parameters, in general, exhibit fluctuations with increasing doping content. Across the entire range of materials studied, a notable trend emerges as the temperature decreases, the magnetization in the zero field cooling curves shows a non-linear decrease, eventually stabilizing in the field cooling branches. The findings suggest that the inclusion of Sc³⁺/Cr³⁺ dopants can be utilized to manipulate and achieve desired magnetic properties in Co–Ni ferrites. The spectra of Mössbauer analysis, which was utilized to establish the distribution of cations, presented four magnetic sextets for all samples. Doped ions are substituted with Fe³⁺ ions at the B site.