Strain-tuned room-temperature spin valve effect in the HfCr2N4 monolayer

Traditional van der Waals spin valves, usually comprising of a nonmagnetic monolayer sandwiched between two ferromagnetic monolayers, present a significant challenge for precise synthesis in contemporary experimental techniques. Can spin valves be implemented with a monolayer compound instead of a van der Waals multilayer heterostructure? Here, we propose a room-temperature HfCr2N4 monolayer spin valve based on density functional theory and Boltzmann transport theory. The HfCr2N4 monolayer is a ferromagnetic half-metal with a high Curie temperature above room temperature. The transition from half-metal to semiconductor can be achieved by manipulating the relative orientation of magnetizations of the Cr atomic layers. Interestingly, the biaxial strain applied in the xy plane is an effective strategy to switch the magnetic configurations. The magnetic ground state of the HfCr2N4 monolayer converts to the antiferromagnetic configuration under -4% strain. Remarkably, the HfCr2N4 monolayer exhibits a substantial room-temperature magnetoresistance ratio of 572%, attributed to variations in band gaps and carrier mobilities. Our findings pave the way for designing future room-temperature monolayer spin valve devices.