Exploring the structural, magnetic, dielectric, and electrochemical properties of Al-doped Cu-Zn nanocrystalline spinel ferrites

In the present study, a series of Cu 0.7 Zn 0.3 Al x Fe 2-x O 4 (0 ≤ x ≤ 0.2) polycrystalline nanoferrites were successfully prepared by the sol-gel combustion method. This work investigates the physical, magnetic, optical, electrical, and electrochemical properties of synthesized samples. Structural characteristics obtained from the X-ray diffraction technique confirm the formation of the cubic spinel structure. The crystallite size was calculated using Debye-Scherrer's formula and decreased from 24 to 11 nm. The Rietveld refinement revealed the (Fd-3m) space group of the prepared samples. The HRTEM technique results in distinct grains with a particle size of around 10 nm for the sample x = 0.2, which supports the XRD results. X-ray photoelectron spectroscopy has confirmed the presence of all elements in the sample and elucidated their electronic states. Fourier Transform Infrared Spectroscopy investigates the presence of two major absorption bands in the regions 577–593 cm −1 (A-site) and 404–422 cm −1 (B-site), confirming the formation of spinel ferrite. UV-Visible measurement shows a linear decrease in the band gap, from ∼1.7 to ∼1.4 eV, with increasing Al 3+ content. Frequency-dependent dielectric measurements were carried out at room temperature, which exhibits a significant contribution of the grains and grain boundaries, following the Maxwell-Wagner type of polarization, which is in accordance with Koop’s theory. The RT magnetic measurements reveal a soft ferrite nature in all samples, showing a lower coercivity (H c ) with increasing Al 3+ concentration. The electrochemical studies show the significant specific capacitance of 658 Fg −1 at a current density of 1 Ag −1 . These outstanding properties render the synthesized samples promising candidates for applications in magnetic devices and energy storage systems.