Bulk spin-orbit torque-driven spin Hall nano-oscillators using PtBi alloys
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| Main Authors: | , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866912481535852544 |
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| author | Shashank, Utkarsh Kumar, Akash Parvini, Tahereh Sadat Heyen, Hauke Zeng, Lunjie Yankovich, Andrew B. Rajabali, Mona Olsson, Eva Münzenberg, Markus Åkerman, Johan |
| author_facet | Shashank, Utkarsh Kumar, Akash Parvini, Tahereh Sadat Heyen, Hauke Zeng, Lunjie Yankovich, Andrew B. Rajabali, Mona Olsson, Eva Münzenberg, Markus Åkerman, Johan |
| contents | Spin-orbit-torque-driven auto-oscillations in spin Hall nano-oscillators (SHNOs) offer a transformative pathway toward energy-efficient, nanoscale microwave devices for next-generation neuromorphic computing and high-frequency technologies. A key requirement for achieving robust, sustained oscillations is reducing the threshold current ($I_{\text{th}}$), strongly governed by spin Hall efficiency ($θ_{\text{SH}}$). However, conventional strategies to enhance $θ_{\text{SH}}$ face trade-offs, including high longitudinal resistivity, interfacial effects, and symmetry-breaking torques that limit performance. Here, we demonstrate a substantial enhancement of the bulk spin Hall effect in PtBi alloys, achieving over a threefold increase in $θ_{\text{SH}}$, from 0.07 in pure Pt to 0.24 in Pt$_{94.0}$Bi$_{6.0}$ and 0.19 in Pt$_{91.3}$Bi$_{8.7}$, as extracted from DC-bias spin-torque ferromagnetic resonance. The enhanced $θ_{\text{SH}}$ originates from bulk-dominated, extrinsic side-jump scattering across all PtBi compositions. Correspondingly, we observe a 42\% and 32\% reduction in $I_{\text{th}}$ in 100 nm SHNOs based on Co$_{40}$Fe$_{40}$B$_{20}$(3 nm)/Pt$_{94.0}$Bi$_{6.0}$(4 nm) and Co$_{40}$Fe$_{40}$B$_{20}$(3 nm)/Pt$_{91.3}$Bi$_{8.7}$(4 nm), respectively. Structural characterization reveals reduced Pt crystallinity, along with emergence of preferred crystallographic orientations upon introducing higher Bi concentrations. Together, these results position PtBi alloys as a compelling alternative to conventional 5$d$ transition metals, enabling enhanced $θ_{\text{SH}}$ and significantly lower $I_{\text{th}}$, thus opening new avenues for energy-efficient neuromorphic computing and magnetic random access memory. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_10219 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Bulk spin-orbit torque-driven spin Hall nano-oscillators using PtBi alloys Shashank, Utkarsh Kumar, Akash Parvini, Tahereh Sadat Heyen, Hauke Zeng, Lunjie Yankovich, Andrew B. Rajabali, Mona Olsson, Eva Münzenberg, Markus Åkerman, Johan Mesoscale and Nanoscale Physics Applied Physics Spin-orbit-torque-driven auto-oscillations in spin Hall nano-oscillators (SHNOs) offer a transformative pathway toward energy-efficient, nanoscale microwave devices for next-generation neuromorphic computing and high-frequency technologies. A key requirement for achieving robust, sustained oscillations is reducing the threshold current ($I_{\text{th}}$), strongly governed by spin Hall efficiency ($θ_{\text{SH}}$). However, conventional strategies to enhance $θ_{\text{SH}}$ face trade-offs, including high longitudinal resistivity, interfacial effects, and symmetry-breaking torques that limit performance. Here, we demonstrate a substantial enhancement of the bulk spin Hall effect in PtBi alloys, achieving over a threefold increase in $θ_{\text{SH}}$, from 0.07 in pure Pt to 0.24 in Pt$_{94.0}$Bi$_{6.0}$ and 0.19 in Pt$_{91.3}$Bi$_{8.7}$, as extracted from DC-bias spin-torque ferromagnetic resonance. The enhanced $θ_{\text{SH}}$ originates from bulk-dominated, extrinsic side-jump scattering across all PtBi compositions. Correspondingly, we observe a 42\% and 32\% reduction in $I_{\text{th}}$ in 100 nm SHNOs based on Co$_{40}$Fe$_{40}$B$_{20}$(3 nm)/Pt$_{94.0}$Bi$_{6.0}$(4 nm) and Co$_{40}$Fe$_{40}$B$_{20}$(3 nm)/Pt$_{91.3}$Bi$_{8.7}$(4 nm), respectively. Structural characterization reveals reduced Pt crystallinity, along with emergence of preferred crystallographic orientations upon introducing higher Bi concentrations. Together, these results position PtBi alloys as a compelling alternative to conventional 5$d$ transition metals, enabling enhanced $θ_{\text{SH}}$ and significantly lower $I_{\text{th}}$, thus opening new avenues for energy-efficient neuromorphic computing and magnetic random access memory. |
| title | Bulk spin-orbit torque-driven spin Hall nano-oscillators using PtBi alloys |
| topic | Mesoscale and Nanoscale Physics Applied Physics |
| url | https://arxiv.org/abs/2507.10219 |