Studies of the microstructural, magnetic, electrical, and dielectric properties of Mg0.6T0.4Cr2O4 (T = Ni, Cu) spinel chromites for magnetic, high frequency, and microwave applications

Abstract

In this study, the structural, morphological, magnetic, electrical, and dielectric properties of Mg0.6T0.4Cr2O4 (T = Ni, Cu) spinel chromites were studied. The X-ray diffraction data reveal that the average crystallite size, lattice constant, and X-ray density increase with the substitution of Ni by Cu. The average crystallite size value rises from 58 nm (for Mg0.6Ni0.4Cr2O4) to 73 nm (for Mg0.6Cu0.4Cr2O4). However, saturation magnetization (Ms) decreases from 0.061 emu/g for Mg0.6Ni0.4Cr2O4 to 0.058 emu/g for Mg0.6Cu0.4Cr2O4. The decline in Ms is due to the lower magnetic moment of Cu2+ ions compared to that of Ni2+ ions. Low Hc coercive fields were obtained (53 Oe and 40 Oe for Mg0.6Ni0.4Cr2O4 and Mg0.6Cu0.4Cr2O4, respectively), indicating that the synthesized samples are suitable for use in soft magnetic devices. Temperature and frequency-dependent impedance spectroscopy measurements have been used to study the samples' electrical properties. The NSPT and CBH models were used to explain the samples' conduction process. Due to the increase in crystallite size, the activation energy (Ea) is lower for Mg0.6Cu0.4Cr2O4 (0.136 eV) than Mg0.6Ni0.4Cr2O4 (0.250 eV). The sample impedance properties were interpreted by modeling Nyquist diagrams considering grain and grain boundary contributions. Dielectric-relaxation phenomenon is observed from sample impedance curves. Mg0.6Ni0.4Cr2O4 conductivity data collapse into a single master curve, as predicted by the Ghosh scaling model. However, for Mg0.6Cu0.4Cr2O4, the Summerfield scaling model is more appropriate. Furthermore, the synthesized materials demonstrate high electrical resistivity, as well as low dielectric constants and losses at higher frequencies, making them appropriate for use in microwave absorption devices and high-frequency applications.