Structure and magnetic properties of (Mg1/6Zn1/6Mn1/6Co1/6Ni1/6Fe1/6)(3)O-4 nanocrystalline high-entropy oxide synthesized using a sol-gel auto combustion approach

Abstract

A sol-gel auto-combustion method is used in this study to synthesize a new class of single-phase high-entropy oxide (HEO) (Mg1/6Zn1/6Mn1/6Co1/6Ni1/6Fe1/6)(3)O-4. The as-synthesized compound exhibits a single-phase spinel structure with an 8.3224 & Aring; lattice parameter and an average crystallite size of 10 nm as determined by X-ray diffraction (XRD) data analysis. Raman and Fourier transform infrared results are in agreement with the XRD results. A scanning electron microscopy-based energy dispersed spectroscopy study suggests the formation of a porous structured morphology with a uniform elemental distribution. In addition, high-resolution transmission electron microscopy and surface analyses further confirm the formation of a pure spinel structure with a particle size of 12-20 nm and a mesoporous character with a pore size of 4.55 nm. X-ray photoelectron spectroscopy indicates mixed-valence states of elements (Mn, Fe, Co, and Ni) and their occupations over tetrahedral and octahedral sites. The temperature-dependent magnetization exhibited a bifurcation between zero-field-cooled and field-cooled magnetizations. From the M-H curves, the magnetization decreased monotonically with the increase in temperature (M is 22 emu/g at 2 K and 7.2 emu/g at 300 K). The coercivity decreased by approximately-one order of magnitude (H-C = 1700 Oe at 2 K and H-C = 200 Oe at 370 K). Finally, a comprehensive magnetic characterization of the as-synthesized HEO indicates their ferrimagnetic nature. The novel physical properties of the as-synthesized HEO could be useful in various potential applications.