Bias-controlled multistate spintronics with giant TMR and polarity switch via localized spin states in 2D half-metals

The relentless downscaling of integrated circuit systems imposes critical demands on spintronic technologies, particularly requiring superior storage density and efficient tunability beyond conventional magnetic-field approaches. A notable challenge persists in realizing multistate spintronic devices with electrical control at nanoscale. Here, we propose a breakthrough strategy for achieving bias-controlled giant tunneling magnetoresistance (TMR) for multistate memory applications. Our design uses two-dimensional (2D) half-metals hosting strongly localized spin states (LSSs) at the Fermi level as two ferromagnet layers in magnetic tunnel junctions (MTJs). Multiple memory states emerge from bias-driven alignment/misalignment of LSSs on two sides, generating sudden tunneling pathway changes and distinguishable TMR. First-principles quantum transport simulations on MTJs based on 2D VCl₃ and FeCl₂ reveal unprecedented bias-controlled and widely modulable TMR ratios spanning -194 to 2677% and -130 to 37,424%, respectively, accompanied by rare polarity switch capabilities. Our work opens a promising route for realizing electrical control of multistate spintronics.