# Room-temperature high spin–orbit torque due to quantum confinement in sputtered BixSe(1–x) films

## Abstract

The spin–orbit torque (SOT) that arises from materials with large spin–orbit coupling promises a path for ultralow power and fast magnetic-based storage and computational devices. We investigated the SOT from magnetron-sputtered BixSe(1–x) thin films in BixSe(1–x)/Co20Fe60B20 heterostructures by using d.c. planar Hall and spin-torque ferromagnetic resonance (ST-FMR) methods. Remarkably, the spin torque efficiency (θS) was determined to be as large as 18.62 ± 0.13 and 8.67 ± 1.08 using the d.c. planar Hall and ST-FMR methods, respectively. Moreover, switching of the perpendicular CoFeB multilayers using the SOT from the BixSe(1–x) was observed at room temperature with a low critical magnetization switching current density of 4.3 × 105 A cm–2. Quantum transport simulations using a realistic sp3 tight-binding model suggests that the high SOT in sputtered BixSe(1–x) is due to the quantum confinement effect with a charge-to-spin conversion efficiency that enhances with reduced size and dimensionality. The demonstrated θS, ease of growth of the films on a silicon substrate and successful growth and switching of perpendicular CoFeB multilayers on BixSe(1–x) films provide an avenue for the use of BixSe(1–x) as a spin density generator in SOT-based memory and logic devices.

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## Acknowledgements

We thank P. Crowell for proofreading the manuscript and M. Kawaguchi for helpful discussions on data analysis. We also thank T. Peterson and G. Stecklein for their help with the PPMS measurements. This work was supported by C-SPIN, one of six STARnet programme research centres. This work utilized (1) the College of Science and Engineering (CSE) Characterization Facility, University of Minnesota (UM), supported in part by the NSF through the UMN MRSEC programme (no. DMR-1420013), and (2) the CSE Minnesota Nano Center, UM, supported in part by the NSF through the NNIN programme. A.M. was supported by the King Abdullah University of Science and Technology (KAUST).

## Author information

Authors

### Contributions

J.P.W., M.DC. and M.J. designed the experiments. J.-Y.C., M.J. and D.Z. grew the samples. M.DC., M.J., Z.Z., H.L., D.Z. and Y.L. designed the experimental set-up. M.DC., H.L. and Z.Z. performed the fabrication of the devices and electrical measurements. J.P.W. proposed the study of the grain-dependent quantum confinement effect on the sputtered BixSe(1–x) films. R.G., T.L. and A.M. carried out the theoretical modelling. D.R.H. and K.A.M. performed the STEM. M.DC., D.Z. and P.Q. did data analysis. M.DC. and J.P.W. wrote the manuscript, and all the authors discussed the results, contributed to the draft of the manuscript and commented on the final version. J.P.W. coordinated the overall project.

### Corresponding author

Correspondence to Jian-Ping Wang.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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## Supplementary information

### Supplementary Information

Supplementary sections 1–11, Supplementary Table 1, Supplementary Figures 1–10, Supplementary References 1–15

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DC, M., Grassi, R., Chen, J. et al. Room-temperature high spin–orbit torque due to quantum confinement in sputtered BixSe(1–x) films. Nature Mater 17, 800–807 (2018). https://doi.org/10.1038/s41563-018-0136-z

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