Magnetic, optoelectronic, and rietveld refined structural properties of Al3+ substituted nanocrystalline Ni-Cu spinel ferrites: An experimental and DFT based study

N. Hasan, S.S. Nishat, S. Sadman, M.R. Shaown, M.A. Hoque, M. Arifuzzaman, A. Kabir

Abstract

The nanocrystalline Ni_0.7Cu_0.3Al_xFe_2-xO₄ (x = 0.00: 0.02: 0.10) are prepared through the sol–gel auto combustion route. The structural, surface morphology, magnetic and optoelectronic properties of Al³⁺ substituted Ni-Cu spinel ferrites have been reported. The crystallinity, phase structure, and structural parameters of the synthesized nanoparticles (NPs) have been determined through X-ray diffraction (XRD) and further refined by maneuvering the Rietveld refinement approach. Both XRD and Rietveld confirm the single phase cubic spinel structure of the investigated materials. Microstructural surface morphology study also confirms the formation of NPs in the highly crystalline state with a narrow size distribution. The Rietveld-refined average crystallite size of the Al³⁺ doped Ni-Cu ferrite nanoparticles falls in the range (61–71 nm), and the average grain size is found to vary from 59 to 65 nm. All other structural parameters refined by the Rietveld refinement analysis are corroborated to single-phase cubic spinel formation of the NPs. Leveraging a vibrating sample magnetometer (VSM), the consequence of Al³⁺ substitution on the magnetic parameters is studied. The saturation magnetization (MS) and Bohr magneton are found to decrease with Al³⁺ substitution. The Remanence ratio and coercivity (H_C) are observed to be very low, suggesting the materials are soft ferromagnetic. First-principle calculations were carried out using the density functional theory (DFT) to demonstrate the optoelectronic behavior of the materials. The electronic bandgap is found low as E_g = 2.99 eV for the explored materials with observing defect states at 0.62 eV. The optoelectronic properties of Al³⁺ substituted Ni-Cu ferrite NPs have been characterized through the DFT simulation for the first time, demonstrating their potentiality for optoelectronic device applications. The materials’ optical anisotropy is observed along the x-axis, which manifests their tunability through light-matter interaction.