All-Altermagnetic Tunnel Junction of RuO 2 /NiF 2 /RuO 2

Abstract Emerging altermagnets with zero net magnetic moment and momentum-dependent spin splitting offer a promising avenue for antiferromagnetic spintronic devices; yet their integration into magnetic tunnel junctions has been hindered by reliance on ferromagnetic electrodes (introducing stray fields) or by limited functionality (non-tunable magnetoresistance without spin filtering). Here, we propose an all-altermagnetic tunnel junction (AAMTJ) paradigm composed exclusively of altermagnets—exemplified by the experimentally feasible RuO 2 /NiF 2 /RuO 2 structure. By introducing an altermagnetic NiF 2 barrier, the achieved tunneling magnetoresistances of 11,704%, 2,496%, and 1,892% for RuO 2 /NiF 2 /RuO 2 are much higher than that of 221% for RuO 2 /TiO 2 /RuO 2 with a nonmagnetic TiO 2 barrier. High spin-filtering efficiencies of ∼90% are also obtained. This architecture unlocks multistate high magnetoresistance and spin filtering via magnetization control of the electrodes and barrier, stemming from their synergistic and antagonistic alignments of momentum-dependent altermagnetic spin splitting. Importantly, high tunneling magnetoresistances are still achieved in the AAMTJ with a TiO 2 spacer in the RuO 2 /TiO 2 /NiF 2 /TiO 2 /RuO 2 configuration. Our AAMTJ inherently exhibits low consumption and zero stray field, with nonrelativistic spin splitting and a vanishing magnetic moment, combining the advantages of both ferromagnetic and antiferromagnetic tunnel junctions. This AAMTJ paradigm opens an interesting avenue within the area of high-performance altermagnet-based tunnel junctions.