RETRACTED ARTICLE: Comparison of the effect of Cr³⁺ substituted Co–Cu and Cu–Co nano ferrites on structural, magnetic, DC electrical resistivity, and dielectric properties

Cr³-substituted Co–Cu (Co_0.7Cu_0.3Fe_2−xCr_xO₄) and Cu-Co (Cu_0.7Co_0.3Fe_2−xCr_xO₄) nano ferrite composites were prepared using the sol–gel approach, where x = 0.0, 0.05, 0.1, 0.15, 0.2, and 0.25. We analysed their structural, DC electrical resistivity, magnetic, and dielectric properties comprehensively. X-ray diffraction (XRD) results indicate the formation of a single-phase spinel ferrite structure. The introduction of Cr³⁺ ions leads to a reduction in lattice volume and crystallite size. Field emission scanning electron microscopy (FESEM) images reveal non-spherical particles on a uniform surface, with a decrease in grain size as Cr³⁺ doping levels increase. The Fourier-transform infrared (FTIR) patterns are consistent with the XRD results, confirming the presence of spinel ferrite. The variation significantly influences the magnetic properties in Cr³⁺ doping. The saturation magnetization (Ms) decreases as the Cr³⁺ content increases to x = 0.1. Beyond that, it continues to decrease with higher Cr³⁺ concentrations. This behavior is attributed to the antiferromagnetic nature of Cr³⁺ ions, which do not favour their occupation at the B sites. The DC resistivity increases with higher Cr³⁺ concentrations and decreases with rising temperatures, indicating the semiconducting behavior of the ferrites. Furthermore, the loss tangent (tanδ) exhibits an exponential decrease with increasing frequency, pointing to typical Maxwell–Wagner-type dielectric dispersion driven by interfacial polarization.