Spin-orbit torque driven by interfacial chemistry in topological BiSb/NiFe bilayers with Ti insertion

Talluri Manoj; Zhenchao Wen; Jun Uzuhashi; Tadakatsu Ohkubo; Hiroaki Sukegawa; Chandrasekhar Murapaka; Brian York; Xiaoyong Liu; Quang Le; Seiji Mitani

Conference poster Spin-orbit torque driven by interfacial chemistry in topological BiSb/NiFe bilayers with Ti insertion

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Talluri Manoj, Zhenchao Wen, Jun Uzuhashi, Tadakatsu Ohkubo, Hiroaki Sukegawa, Chandrasekhar Murapaka, Brian York, Xiaoyong Liu, Quang Le, Seiji Mitani. Spin-orbit torque driven by interfacial chemistry in topological BiSb/NiFe bilayers with Ti insertion. https://doi.org/10.48505/nims.5051

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In this work, BiSb thin films with a NiFe ferromagnetic layer were prepared to explore the impact of Ti spacer insertion on SOT efficiency. Remarkably, the Ti spacer layer enhanced SOT efficiency, persisting after aging and annealing, offering insights into interfacial interdiffusion for improved spintronics applications.
Two samples, BiSb/NiFe and BiSb/Ti/NiFe, were compared under different conditions, i.e., as-deposited, room-temperature aged for 45 days, and annealed at 400 K for 1 h. After deposition of BiSb, RHEED patterns revealed semi-polycrystalline growth, with improved crystallinity observed after annealing. The AFM image displayed a remarkably flat surface with an average roughness of 0.7 nm for the as-deposited 8-nm-thick BiSb thin film. Thickness-dependent resistivity measurements for the BiSb thin films illustrated the emergence of topological surface states, with increased resistivity in thicker films. XRD spectra confirmed the existence of a robust (001)-texture of the BiSb thin films, particularly in films thicker than 8 nm. Subsequently, ST-FMR measurements demonstrated an enhanced SOT efficiency of 1.2, achieved in the sample with a Ti spacer layer, which is around 4 times higher than in the sample without the Ti layer. The enhancement of SOT efficiency could be attributed to protecting topological surface states and preventing interdiffusion due to the Ti insertion. Microstructural analysis from cross-sectional STEM indicated an improved crystallinity in the Ti-inserted sample after annealing. Elemental analysis revealed the role of Ti in suppressing interdiffusion and preserving topological properties, contributing to the substantial increase in the SOT efficiency.

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