Multi-Method Characterization of the High-Entropy Spinel Oxide Mn0.2Co0.2Ni0.2Cu0.2Zn0.2Fe2O4: Entropy Evidence, Microstructure, and Magnetic Properties

Abstract

The novel spinel Cu_0.2Co_0.2Mn_0.2Ni_0.2Zn_0.2Fe₂O₄ comprising six transition metal cations was successfully prepared by a solution-combustion method followed by distinct thermal treatments. The entropic stabilization of this hexa-metallic material is demonstrated using in situ high temperature powder X-ray diffraction (PXRD) and directed removal of some of the constituting elements. Thorough evaluation of the PXRD data yields sizes of coherently scattering domains in the nanometre-range. Transmission electron microscopy based methods support this finding and indicate a homogeneous distribution of the elements in the samples. The combination of ⁵⁷Fe Mössbauer spectroscopy with X-ray absorption near edge spectroscopy allowed determination of the cation occupancy on the tetrahedral and octahedral sites in the cubic spinel structure. Magnetic studies show long-range magnetic exchange interactions which are of ferri- or ferromagnetic nature with an exceptionally high saturation magnetization in the range of 92–108 emu g⁻¹ at low temperature, but also an anomaly in the hysteresis of a sample calcined at 500 °C.