All-Altermagnetic Tunnel Junction of RuO₂/NiF₂/RuO₂

Emerging altermagnets with zero net magnetic moment and moment-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 experimentally feasible RuO₂/NiF₂/RuO₂. By introducing an altermagnetic NiF₂ barrier, the achieved tunneling magnetoresistances of 11,704%, 2,496% and 1,892% for RuO₂/NiF₂/RuO₂ are much higher than that of 221% for RuO₂/TiO₂/RuO₂ with a nonmagnetic TiO₂ 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 TiO₂ spacer of RuO₂/TiO₂/NiF₂/TiO₂/RuO₂. Our AAMTJ inherently exhibits low consumption and zero stray field, with nonrelativistic spin splitting and 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.