Bidirectional spin-filtering effects in altermagnetic spin field-effect transistors

Realizing ideal and bidirectionally controllable spin-filtering effects in a single material is essential for the advancement of short-channel spin field-effect transistors (spin-FETs). Such advancements can significantly enhance logical operation capabilities, functional diversity, signal processing prowess, stability, and integration density while reducing power consumption. However, it remains challenging. In this study, using first-principles calculations, we demonstrate that the spin-FET based on the altermagnetic monolayer Ca(CoN)2 with spin–layer coupling can achieve perfect and controllable spin filtering depending on the transport direction. Notably, at zero gate voltage, the spin-FET exhibits a remarkable 100% spin-filtering efficiency (SFE) for spin-up and spin-down electrons along the [100] and [010] transport directions, respectively. Interestingly, due to the spin–layer coupling inherent in the monolayer Ca(CoN)2, the application of gate voltage can effectively modulate the SFE and improve the current in the [110] transport direction. Specifically, a positive (or negative) gate voltage enhances the SFE to 100% of spin-down (or spin-up) currents. Our findings provide viable strategies for the development of high-performance spintronic devices based on altermagnetic materials.