Impact of Co2+ on the spectral, optoelectrical, and dielectric properties of Mg0.25Ni0.25Cu0.5−xCoxFe1.97La0.03O4 ferrites prepared via sol–gel auto-combustion route

Spinel ferrites are attaining huge importance in the modern era, due to their incredible properties, which means they are widely used in various fields. Therefore, in this paper a cost-effective and environmentally friendly preparation of Mg0.25Ni0.25Cu0.5−xCoxFe1.97La0.03O4 (x = 0.0, 0.125, 0.25, 0.375, and 0.5) ferrites via the sol–gel auto-combustion method were carried out. How the structural and functional properties varied with the Cu to Co ratio was studied. It was found that the crystallite size (D) was reduced from 47.2 to 27.6 nm as the Co2+ increased from x = 0.0 to 0.5. While the two major absorption bands including the higher frequency band (υ1) and lower frequency band (υ2) lie in the range of 573.80–538.65 cm−1 and 470.37–405.65 cm−1 belong to the spinel matrix. Five active Raman modes were found in the range of wave number 200–800 cm−1 corresponds to the sublattices of the spinel structure. The optical bandgap increased from 0.85 eV to 1.33 eV for x = 0.0 to x = 0.25 and then observed optical band gap was 1.15 eV and 1.46 eV for x = 0.375 to x = 0.5. The resistivity (ρ) was minimum for Co2+ concentration x = 0.25 at low temperature, while at high temperature the resistivity (ρ) was maximum for Co2+ doping x = 0.25. The temperature coefficient of resistance percentage (TCR %) was −2.66%/K at 513 K for x = 0.25, as shown in the graphical abstract. At lower frequencies, the impedance was observed maximum for Co2+ doping x = 0.125 and minimum for x = 0.375. These findings indicate that the as-prepared ferrites are a potential candidate for optoelectrical and bolometric devices.