Tunable magnetic ordering through cation selection in entropic spinel oxides

Twelve multicomponent spinels, comprised of (Mg, Cr, Mn, Co, Fe, Ni, Cu, and/or Zn)(Cr, Fe, or Al)(2)O-4, were prepared using solid state synthesis methods, resulting in nine homogenous, single phase samples with a Fm-3m structure, and three samples with multiple phases. Using dc magnetometry in conjunction with x-ray diffraction, scanning electron microscopy with energy dispersive x-ray spectroscopy, and x-ray absorption spectroscopy, the effects of multicomponent material design on the structural, magnetic, and chemical properties are explored. The ferritic spinel high-entropy oxide (HEO) samples show high-temperature ferrimagnetic transitions and both ferritic and chromium-based HEO spinel samples show evidence of low-temperature antiferromagnetic ordering. Blocking temperatures are evident in some samples and magnetic transition temperatures are reported. Constituent valence states and temperature dependent valence is described for the example case of (Mg0.2Fe0.2Co0.2Ni0.2Cu0.2)Cr2O4, including the unexpected presence of Cr4+, indicating a 2-4 type spinel configuration. Valence trends for two ferritic HEO spinels are also discussed. Some of these compositions are synthesized for the first time and this work provides an investigation into the magnetic properties of the novel class of cubic spinel multicomponent oxides showing interesting behavior that warrants further investigation.