Strong correlation of electrical transport and magnetic properties to ionic states, structure, and morphology of Al-substituted Ni–Co ferrite systems: A comprehensive study

This paper presents the structure, morphology, magnetic, ionic states, and electrical transport characteristics of spinel Ni_0.5Co_0.5Al_xFe_2-xO₄ (x = 0.0, 0.5, and 1.0) nanocrystalline ferrites, synthesized by using the sol-gel auto-combustion method. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to analyze the structural characteristics. The synthesized ferrites were found to have a crystallite size of less than 40 nm when the Rietveld method was applied to refine XRD patterns in single-phase cubic spinel-related structures that belong to the Fd-3m space group. Furthermore, since the ionic states are visible in X-ray photoelectron spectroscopy (XPS), variations in Al³⁺ ion concentration have been found to affect the locations, occupancy, and Wyckoff's cationic position of the ions as well as the lattice constant (a), the crystallite size (D), and the micro-strain of the composites. Thermogravimetric analysis was used to examine the temperature-dependent spinel phase formation and % weight loss of the sample. The x = 1.0 composition is said to be the best dielectric material out of the three samples since it has the highest polarization permittivity, the lowest dissipation factors, and exceptional temperature stability. These nanoparticles have relatively high impermanent magnetization values and are ferrimagnetic, according to the vibrating sample magnetometer (VSM) investigation. Additionally, it was found that the presence of Al³⁺ decreases the magnetization values of the spinel Ni_0.5Co_0.5Al_xFe_2-xO₄ (x = 0.0, 0.5, and 1.0) system because the Al³⁺ exclusively occupies the Fe-sites, which reduces the super-exchange interaction between the Fe²⁺/Fe³⁺, Co²⁺/Co³⁺, and the Ni²⁺/Ni³⁺ ions. The unique magnetic characteristic of these compositions below 40 nm is predicted to make them appealing for storage applications.