Structural, magnetic, dielectric and specific capacitance investigation of cobalt-doped zinc ferrite for energy storage devices

The chemical co-precipitation approach was used to synthesize cobalt-zinc ferrite with the composition CoxZn1xFe2O4 (x = 0.0, 0.3, 0.5, 0.7 and 1.0). X-ray diffraction (XRD) confirmed the formation of a single spinel phase. The lattice parameter decreases with the increase in Co2+ ion concentration. Fourier transform infrared spectroscopy (FT-IR) provided evidence of the presence of bond characteristics of spinel structures. Spherical morphology with minor agglomeration was observed from the high-resolution transmission electron microscopy (HRTEM) and the average particle size is in the range of 15 nm and 20 nm. The magnetic properties of the synthesized samples were investigated through a vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR) spectroscopy. Both the saturation magnetization and coercivity increased with an increase in Co2+ content, with the maximum magnetization of value 53.4 emu/g recorded for the composition Co0.7Zn0.3Fe2O4. The increase in Co2+ ions concentration results in the M-H hysteresis loop shifting from a paramagnetic to a ferromagnetic nature. EPR spectra depict the changes in the broad line as the cobalt concentration rises, with a clear trend of broadening the signal as Co concentration rises. The dielectric analysis was carried out on a frequency range of 10-1 to 106 Hz by varying temperature from 30 to 130 degrees C. Dielectric analysis of prepared samples shows frequency-dependent behaviour for both dielectric constant and dielectric loss tangent giving maximum values at lower frequencies and decreasing thereafter, however, temperature also enhances their values. Higher values for dielectric constant are observed at higher concentrations of cobalt ions. The synthesized materials were subsequently tested for their electrochemical properties and potential applications in supercapacitors. The CV measurements revealed that Co0.7Zn0.3Fe2O4 shows excellent electrochemical properties in comparison with other samples as well as with the literature.