All-Altermagnetic Tunnel Junction of RuO₂/NiF₂/RuO₂

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 \sim90% 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.