Giant tunneling magnetoresistance in altermagnetic heterostructures via multi-stage spin-filtering

Altermagnets, which combine the advantages of ferromagnetic spin splitting and antiferromagnetic zero stray field, have been regarded as a promising platform for spintronic applications. However, it is challenging to achieve high tunneling magnetoresistance (TMR) in altermagnet-based tunnel junctions due to the momentum-dependent spin splitting. By leveraging the intrinsic spin-dependent tunneling asymmetry of altermagnetic (AM) insulators, we investigate spin-polarized transport properties in altermagnetic tunnel junctions (AMTJs) with fully altermagnetic heterostructure barriers using first-principles quantum-transport calculations. Specifically, we design and compare [110]-oriented heterostructured AMTJs composed of IrO2/CoF2/MF2/CoF2/IrO2 (M = Fe, Mn) with a homogeneous CoF2-barrier reference. Our results show that the FeF2-based heterostructure achieves giant TMR ratios of up to 196,468%, while the MnF2-based counterpart yields substantial values up to 2,322%, far exceeding the modest 14% obtained for the homogeneous CoF2 barrier system. Mechanistically, this enhancement originates from a multi-stage spin-filtering effect enabled by the heterostructured barriers, which breaks the single transport-mode constraint of homogeneous barriers through the symmetry-selective superposition of spin states. These findings highlight the potential of staggered altermagnetic heterostructures to overcome the single-mode transport limitation of conventional MTJs, providing a robust pathway toward next-generation high-performance altermagnetic spintronic devices.