Role of copper doping on cation redistribution, spectroscopic and magnetic characteristics of Ni0.5−xCo0.5−xCu2xFe2O4 spinel ferrites

Abstract In this investigation, samples of type Ni _0.5−x Co _0.5−x Cu _2x Fe ₂ O ₄ with x = 0.00, 0.02, 0.04, 0.08, 0.12, and 0.20 were generated using the chemical co-precipitation technique. Refined X-ray powder diffraction (XRD) data confirmed the presence of a cubic spinel ferrite structure, while a minor peak corresponding to hematite α-Fe ₂ O ₃ was also detected. The average lattice constant increased from 8.348 Å to 8.363 Å with increasing Cu doping. Crystallite sizes ranged from 24 to 39 nm. Transmission electron microscopy (TEM) images indicated that the particles were predominantly spherical and exhibited aggregation, especially in the undoped sample. The selected area electron diffraction (SAED) pattern’s rings clearly revealed the sample’s polycrystalline nature. Raman spectra confirmed the formation of the spinel phase in the synthesized samples, as evidenced by the emergence of the five active Raman optical modes. A plausible model for cationic distribution has been constructed based on Raman findings and the site preferences of metal ions (Ni ²⁺ , Co ²⁺ , Cu ²⁺ , and Fe ³⁺ ) for tetrahedral (A) and octahedral (B) positions. It was found that the samples undergo nearly inverse spinel structures. Furthermore, Fourier transform infrared (FTIR) spectra confirmed the spinel ferrite structure with space group Fd3m. X-ray photoelectron spectroscopy (XPS) was employed to determine the oxidation states of the constituent elements. Moreover, room-temperature M-H hysteresis loops demonstrated the ferromagnetic behavior of the Ni _0.5−x Co _0.5−x Cu _2x Fe ₂ O ₄ samples. The observed variations were interpreted using Neel’s collinear two-sublattice and Yafet-Kittel’s three-sublattice models. The law of approaches to saturation (LAS) was applied to analyze the magnetization curves in six different forms.