Theoretical and Experimental Investigation of Magneto-Optical Properties of Ferrite Nanoparticles Synthesised from Nigerian Mineral Resources

Ferrite nanoparticles exhibiting coupled magnetic and optical responses are of fundamental scientific interest and offer potential applications in magnetic resonance imaging contrast agents, microwave absorbers, and magneto-optical sensors. Nigeria possesses abundant iron ore deposits and associated mineral resources in Kogi, Kwara, and Enugu states from which ferrite precursor materials can be sustainably derived. This study conducts a combined theoretical and experimental investigation of the magneto-optical properties of manganese-zinc ferrite and nickel-zinc ferrite nanoparticles synthesised from iron ore concentrates and co-precipitated with laboratory-grade manganese, zinc, and nickel salts. Nanoparticle structure is characterised by XRD Rietveld refinement, TEM, and Mossbauer spectroscopy. Magnetic properties including saturation magnetisation, coercivity, and anisotropy constant are measured by vibrating sample magnetometry. Magneto-optical Kerr rotation spectra are recorded from 300 to 800 nm. Density functional theory calculations within the DFT+U framework are performed to compute the electronic band structure, density of states, and magneto-optical conductivity tensor of the synthesised compositions. Results demonstrate that Mn-Zn ferrite nanoparticles of 12 nm diameter exhibit superparamagnetic behaviour with magnetisation of 48 emu per gram and a Kerr rotation of 0.12 degrees at 532 nm. The DFT-computed Kerr spectra agree with measured values within 15 percent. Keywords: ferrite nanoparticles, magneto-optical, DFT+U, Nigeria mineral resources, superparamagnetism