Magnetic structure determination of the first high pressure, high entropy oxide

High entropy oxides (HEOs) are a family of materials with extreme configurational disorder – but how their entropic forces interact with external conditions such as high pressure remains an unexplored arena. We have succeeded in synthesising the first high pressure, high entropy oxide. The material, which forms at 15 GPa, has the nominal composition (Cr,Mn,Fe,Co,Ni)4O5, and crystallises in the orthorhombic Cmcm space group, making it one of the first non-cubic HEOs. Early characterisation shows remarkably complex magnetic order, with enigmatic features that cannot be disentangled without more advanced techniques. X-ray absorption spectroscopy shows mixed site occupancies, while confirming a trend of suppressed configurational entropy in HEOs composed of 3d transition metals. Our proposed experiment will utilise neutron powder diffraction to solve the material’s magnetic structure, and explore its evolution as a function of temperature. The chemical complexity and magnetic nature of our system makes neutron diffraction an invaluable tool to answer these pressing questions. Our results will represent a significant contribution to our understanding of the evolution of properties in HEOs, and the interactions between magnetism and disorder in complex materials.