Boosting the high bias TMR in ferromagnet/superconductor hybrids with spin-orbit interaction

Spin-resolved electron symmetry filtering is a key mechanism behind giant tunneling magnetoresistance (TMR), providing room temperature functionality in magnetic tunnel junctions (MTJs). However, it breaks down under applied bias, reducing the TMR above 0.5 V. Here we show a new approach based on spin orbit coupling (SOC) controlled interfacial states in vanadium, providing a strong TMR boost under applied bias in V/MgO/Fe/MgO/Fe/Co structures [1]. The observed increase of TMR is modelled with two nonlinear resistances in series, with the low bias conductance of the first (V/MgO/Fe) being boosted by the SOC-controlled interfacial states, while the second (Fe/MgO/Fe) depends on the alignment of the ferromagnetic layers. At low temperatures, the TMR reduction has been mitigated by using resonant tunneling through quantum well states in thin layers. We have also studied the conductance features of our junctions in the superconducting regime of vanadium (below 4 K), finding periodic features consistent not only with this quantum well states, but also with Andreev reflection processes giving rise to long-range triplet Cooper pairing, which is a promising feature in the emerging field of superconducting spintronics. [1] C. González-Ruano et. al. Adv. Electron. Mater. 2100805 (2021).