Ferrimagnetism in High Entropy Transition Metal Spinel Oxides

High entropy oxides (HEOs) have a crystal structure comprised of chemically ordered oxygen anions and an equimolar proportion of five metal cations randomly distributed over their sublattice. The imposition of large disorder allows configurational entropy to overcome the enthalpy of formation and stabilize a new high entropy phase. HEOs have potential applications ranging from ferroic multifunctionality to reversible energy storage. Studies of the magnetic properties of HEOs to date have been limited to (MgCoNiCuZn)_0.2O, which has a rock-salt structure. This material undergoes a long-range antiferromagnetic ordering transition at T_N=113K despite intense disorder and a 40% magnetic dilution. Here, we present the discovery of three 3d-transition metal based ferrimagnetic spinel type HEOs. The high entropy phase is confirmed by Rietveld refinement of powder x-ray diffraction data and elemental microprobe analysis. Magnetic susceptibility measurements of these HEOs suggest that all three transition into ferrimagnetic ordered states between T=300K and 400K, followed by a spin reorientation around 100K. In this talk we will present a robust characterization of their magnetic and electronic ground states via heat capacity and resistivity measurements.