Magnetic properties and ionic distribution in high entropy spinels studied by Mössbauer and ab initio methods

Structural and magnetic properties of three high entropy oxide spinels (Cr,Mn,Fe,Co,Ni)${}_3$O${}_4,$ (Cr,Mn,Fe,Co)${}_3$O${}_4$ and (Cr,Mn,Fe,Ni)${}_3$O${}_4$ were investigated in a wide temperature range. VSM magnetic measurements (at 4K) allowed for determination of the average magnetic moment, being nearly twice smaller than that of magnetite. Magnetic ordering temperatures were determined using Mössbauer spectroscopy (80-670K). Characteristic features of the Mössbauer spectra prove significant influence of broad quadrupole splitting distribution on their shape. On the other hand they were found to be symmetric enough to exclude different oxidation states of Fe for nonequivalent sites. On the basis of the electronic structure calculations slight preferences for cobalt (but not iron) site occupancy were found.