Transition to a Half-Metal Leading to a Drastic Decrease in the Electrical Resistance of the High-Entropy Oxide (MgCoNiCuZn)O at High Pressure.

Abstract

High-entropy materials often exhibit properties unexpected from their simple components. Prior studies showed that as the pressure increased from 0 to ∼40 GPa, the electrical resistance of the high-entropy oxide (HEO) (MgCoNiCuZn)O decreased more than 3 orders of magnitude, far beyond the expected value based on the changes in the semiconductor bandgap and carrier mobility. To tackle this enigma, we used different density-functional theory (DFT) computational methods to study the electronic band structures of the HEO at different pressures. It was found that the DFT+<i>U</i>+2% HF method best reproduced the experimentally observed pressure-dependent characteristics of both the resistance and optical bandgaps of the HEO. The calculations revealed the complex band structures of the HEO under high pressure, exhibiting spin-up bandgaps, spin-down bandgaps, a spin-down middle bandgap, and secondary optical transition bandgaps. Some of the spin-resolved bandgaps close at high pressure, leading to a transition of the HEO from a semiconductor to a half-metal, which causes a significant decrease in the resistance above ∼20 GPa. The half-metallization was further confirmed by the Boltzmann transport property calculations. This work unveils that the HEO (MgCoNiCuZn)O is a promising pressure-sensitive spintronics material not recognized before.