Large Spin Polarization from symmetry-breaking Antiferromagnets in Antiferromagnetic Tunnel Junctions

Efficient detection of magnetic states is essential for the development of antiferromagnet-based spintronic devices. Although finite tunneling magnetoresistance (TMR) has been observed in tunnel junctions with antiferromagnetic (AFM) electrodes, most research has focused on junctions with two identical AFM electrodes, where matching spin-split Fermi surfaces is key. It remains uncertain whether AFMs can produce a net spin polarization, making them suitable as spin polarizers or detectors. In this study, we fabricate single-sided antiferromagnetic tunnel junctions with one AFM electrode (Mn3Sn) and one ferromagnetic (FM) electrode (CoFeB), detecting spin-polarized tunneling from the AFM via the FM layer. At cryogenic temperatures, we observe high TMR (>100% at 10 K) in these asymmetric junctions, indicating significant spin polarization from Mn3Sn, despite its nearly negligible magnetization. This observation aligns with recent theoretical predictions that broken symmetry in non-collinear AFMs removes spin degeneracy in their band structure. Our findings provide compelling evidence that AFMs can enable spin-polarized electrical transport.