Cr-modified CoFe₂O₄ nano ferrites: a study of structural, morphological, electrical, dielectric, magnetic and magneto dielectric evolution

Using the sol-gel auto combustion approach, nanoferrites of the CoCr_xFe_2−xO₄ series (x = 0.00, 0.05, 0.10, 0.15, 0.20) are fabricated. Lattice constants are computed within the range of 8.312–8.375 Å, while crystallite size, estimated using Scherrer method yields ranges from 55.20 to 34.79 nm. Using Fourier transform infrared (FTIR) spectroscopy, different functional groups are found to correlate to different absorption bands. Five active modes are identified by Raman spectroscopy, revealing O²⁻ion vibrations at both tetrahedral and octahedral locations. Throughout the series, ferromagnetic hysteresis loop is observed which is explained by Neel’s model. When the doping concentration increases in the Fe²⁺ site the ac conductivity are found to decrease with increase in Cr³⁺ doping content. With increasing frequency, both the dielectric constant and dielectric loss increase. In addition, with an increase in Cr³⁺ doping, saturation magnetization (M_s), remnant magnetization (M_r), and coercivity (H_c) show declining trends. For applications involving microwave devices, the sample CoCr_0.2Fe_1.8O₄shows the most promising magnetic behavior, with M_s ranging from 73.12 to 39.71 emu/g, M_r from 37.77 to 20.64 emu/g, and H_c from 1939 Oe to 1200Oe throughout the series.