Large unidirectional spin Hall magnetoresistance in FeNi/Pt/Bi₂Se₃ trilayers by Pt interfacial engineering

Unidirectional spin Hall magnetoresistance (USMR) has emerged as a promising candidate for magnetoresistive random-access memory (MRAM) technology. However, the realization of high signal-to-noise output signal in USMR devices has remained a challenge, primarily due to the limited USMR effect at room temperature. In this study, we report a large USMR effect in FeNi/Pt/Bi₂Se₃ trilayers through interfacial engineering with Pt to optimize the spin current transmission efficiency and electron-magnon scattering. Our devices exhibit a USMR value that is an order of magnitude higher than previously reported systems, reaching 30.6 ppm/MA/cm² at room temperature. First-principles calculations and experimental observations suggest that the Pt layer not only preserves the spin-momentum locked topological surface states in Bi₂Se₃ at the Fermi-level but also generates additional Rashba surface states within the Pt itself to enhance the effective SOT efficiency. Furthermore, we demonstrate that the two-terminal USMR-MRAM devices show robust output performance with 2^nd harmonic resistance variation around 0.11 Ω/mA. Remarkably, the performance of these devices further improves at elevated temperatures, highlighting their potential for reliable operation in a wide range of environmental conditions. Our findings pave the way for future advancements in high-performance, energy-efficient spintronic memory devices.