Altermagnetic-RuO2-based all-magnetic tunnel junction: Giant and multistate tunneling magnetoresistances with perfect spin filtering

Abstract

Altermagnets generate momentum-dependent spin-polarized currents without net magnetization, offering an intriguing platform for spintronic applications. However, altermagnet-based tunneling devices often possess limited magnetoresistance tunability or rely on conventional, highly spin-polarized ferromagnetic (FM) electrodes with stray fields. Here, we propose an all-magnetic tunnel junction paradigm by integrating experiment-feasible altermagnetic (AM) RuO2 electrodes with a FM/antiferromagnetic (AFM) CrOCl barrier. Utilizing density functional theory combined with the non-equilibrium Green's function methods, we demonstrate that the RuO2/CrOCl/RuO2 junction achieves multistate, nonvolatile spin transport through synergistic and antagonistic magnetization alignments between the AM source and the FM/AFM barrier. Remarkably, this design yields an exceptionally high tunneling magnetoresistance (TMR) of 1.8 × 105% and perfect spin filtering efficiency of ∼100%. The TMR is broadly tunable from 42% to 504% with a monolayer barrier and from 1% to ∼105% with a bilayer barrier. The resistance-area products from 0.74 × 10−3–4.5 × 10−3 Ω μm2 (monolayer) to 3.1 × 10−3–5.7 Ω μm2 (bilayer) lie within the practical range for magnetic memory applications. Our work establishes the fusion of AM electrodes with FM/AFM barriers as a feasible strategy to unlock multiple controllability and get rid of FM electrodes, opening avenues for high-performance multi-bit memory and reconfigurable logic devices.