Copper-doped sputtered BiSb topological insulators for field-free perpendicular magnetization switching via out-of-plane spin polarization

Haotian Duan; Hongna Gu; Zeyi Zhu; Zishuang Li; Yi Huang; Lina Chen; Mengdi Yin; Lijun Ni; Kankan Xu; Xuefeng Wang; Yongbing Xu; Bo Liu; Tiejun Zhou; Ronghua Liu

doi:10.1103/s1v5-qrtc

Copper-doped sputtered BiSb topological insulators for field-free perpendicular magnetization switching via out-of-plane spin polarization

Haotian Duan ¹, Hongna Gu¹, Zeyi Zhu¹, Zishuang Li¹, Yi Huang ¹, Lina Chen^2,3, Mengdi Yin^1,6, Lijun Ni⁴, Kankan Xu⁵ et al.

Xuefeng Wang ^5,6, Yongbing Xu^5,6, Bo Liu⁷, Tiejun Zhou⁷, and Ronghua Liu ^1,6,*

¹State Key Laboratory of Spintronics and School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
²School of Science, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
³National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China
⁴College of Nuclear Equipment and Nuclear Engineering, Yantai University, Yantai 264005, China
⁵School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
⁶State Key Laboratory of Spintronics, Nanjing University, Suzhou 215163, China
⁷State Key Laboratory for Spintronic Devices and Technologies, Hangzhou 311305, China

^*Conatact author: rhliu@nju.edu.cn

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Phys. Rev. Materials 10, 064201 – Published 2 June, 2026

DOI: https://doi.org/10.1103/s1v5-qrtc

Abstract

Spin-orbit torque (SOT) magnetoresistive random-access memory (MRAM), a nonvolatile memory technology, exhibits promising prospects for advancing memory devices. However, it still faces pivotal challenges in achieving high SOT efficiency and realizing deterministic field-free switching in perpendicular magnetization SOT devices. Herein, we propose an effective strategy to realize high-efficiency field-free switching with an ultralow critical current density $(J_{c} = 3.9$ $MA / c m^{2})$ by doping copper (Cu) into the topological insulator (TI) ${Bi}_{0.9} {Sb}_{0.1}$ (BiSb). The cosputtered Cu-BiSb alloy film achieves a high conventional transverse spin polarization efficiency $(ξ_{y, DL} = 0.53)$ . In contrast to undoped BiSb, it exhibits a significant fieldlike torque induced by spin currents with out-of-plane spin polarization $(ξ_{z, FL} = 0.55)$ . This unconventional spin polarization enables deterministic field-free switching of perpendicular magnetization with as low as $J_{c} \sim 4$ $MA / c m^{2}$ in Cu-BiSb/Pt/Co/Pt heterostructures. Our work provides critical support for the development of TI-based, high-performance, and integrable SOT-MRAM devices.

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Copper-doped sputtered BiSb topological insulators for field-free perpendicular magnetization switching via out-of-plane spin polarization

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Copper-doped sputtered BiSb topological insulators for field-free perpendicular magnetization switching via out-of-plane spin polarization

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