Large Magnetoresistance and Perfect Spin-Injection Efficiency in Two-Dimensional Strained VSi2N4-Based Room-Temperature Magnetic-Tunnel-Junction Devices

Two-dimensional (2D) materials provide a promising platform for exploring spintronic devices. How-ever, the low Curie temperature of most 2D magnetic materials limits their development and application. Based on density-functional theory and the nonequilibrium-Green's-function formalism, we present a sys-tematic simulation study of room-temperature strained VSi2N4-based magnetic tunnel junctions (MTJs), using a high-accuracy Heyd-Scuseria-Ernzerhof (HSE) functional. In contrast to Perdew-Burke-Ernzerhof results, a spin-conductance match is observed in Ag/VSi2N4-VSi2N4/Ag MTJs at the HSE06 level. Thus, a 1200% tunnel-magnetoresistance (TMR) ratio and a perfect spin-injection efficiency are theo-retically predicted in Ag/VSi2N4-VSi2N4/Ag MTJs. Interestingly, the coexistence of a Weyl semimetal and a half-metal state is found in 1.965% tensile-biaxial-strained monolayer VSi2N4. In addition, a slight compressive strain leads to a boost of the TMR ratio by 2 orders of magnitude, up to 105% in strained VSi2N4-based MTJs. Other MTJs based on VSi2P4, VSi2As4, and NbSi2N4 are investigated. Our results show that these spin-polarized magnetic silicide compounds, with Curie temperatures close to room temperature, are promising candidates for next-generation spintronic devices.