Low-temperature Griffiths phase in chemically synthesized CoMn2O4 spinel oxide

Mixed transition metals and their oxides have gained a myriad of research interests because of their wide applications in electronics, magnetism, and electrochemical energy storage and conversion devices. In this study, we have synthesized CoMn2O4 spinel oxide through the auto-combustion method. At room tem-perature, the x-ray diffraction technique confirms the tetragonal crystal structure and phase purity. The Fourier transform infrared spectroscopy investigated that the oxide and hydroxyl groups are the major active sites. The absorption bands around 544 cm-1 and 638 cm-1 correspond to the atomic vibration of Co -O and Mn-O in octahedral and tetrahedral sites, respectively. The bandgap confirmed from the UV-Vis spectrum is 1.3 eV, indicating that synthesized sample is near-infrared light active material. The scanning electron microscopy shows that the average particle size of CoMn2O4 is 161 +/- 26 nm. X-ray photoelectron spectra suggest a mixed spinel structure comprised of Co and Mn cations. The magnetic investigations revealed that the CoMn2O4 exhibits a ferrimagnetic response. However, the emergence of large exchange bias is observed well above the transition temperature of similar to 172 K due to the Griffiths phase. It is proposed that the appearance of Griffiths phase arises due to the presence of antiferromagnetic impurities, which become active at low temperature.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

Mixed transition metals and their oxides have attracted significant research attention due to their wide range of applications in electronics, magnetism, and electrochemical energy storage and conversion devices. In this study, CoMn2O4 spinel oxide was synthesized through the auto-combustion method, with the structure and phase purity confirmed by X-ray diffraction. The oxide and hydroxyl groups were identified as the major active sites through Fourier transform infrared spectroscopy. The synthesized sample exhibited near-infrared light activity with a bandgap of 1.3 eV, as determined by UV-Vis spectroscopy. The average particle size of CoMn2O4 was found to be 161 +/- 26 nm through scanning electron microscopy. X-ray photoelectron spectra showed a mixed spinel structure containing Co and Mn cations. Magnetic investigations revealed a ferrimagnetic response in CoMn2O4 and the emergence of a large exchange bias above the transition temperature due to the presence of Griffiths phase.