Magnetic and lattice thermodynamics in bulk rock salt high-entropy oxides

High entropy oxides feature high configurational entropy related to site occupancy disorder and exhibit several interesting functional properties, such as colossal dielectric constants, superionic conductivity, and low thermal conductivity. We will report on neutron scattering studies of the magnetic structure and dynamics in the prototypical (Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O[1] and the new (Mg_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O [2] rock salt high entropy oxides featuring divalent 3d transition metals.[1] At low temperature, neutron diffraction reveals long-range magnetic order with (1/2,1/2,1/2) propagation vector, an order that survives the extreme configurational disorder, with short range order subsisting even at room temperature. The phase transition is continuous over an extended temperature range. The insights from neutron scattering will be presented in the light of Mössbauer spectroscopy,[2] calorimetry,[1-3] and muon spin resonance.[3]