VP23-01 Orbitronics for Energy-Efficient Magnetization Switching
Creators: Yuxuan Yao
Daoqian Zhu
Qingtao Xia
Jianing Liang
Yuhao Hao
Zhiyang Peng
Jiaxu Li
Chen Xiao
Renyou Xu
Wenwen Wang
Xiantao Shang
Shiyang Lu
Dapeng Zhu
Hongxi Liu
Kaihua Cao and Weisheng Zhao
Publisher: name: IEEE
Year: 2025

Spin-orbit torque (SOT), as a promising writing method for magnetic random-access memory (MRAM), has garnered widespread interest for over a decade [1,2]. Heavy metals, such as β-W, have been broadly adopted as spin current sources, but suffer from a drastic drop of charge-to-spin conversion efficiency at a limited thickness [3]. This poses challenges for simultaneously satisfying SOT efficiency, etching-stop margins, and back-end-of-line (BEOL) compatibility. Orbitronics brings new opportunities for addressing these issues by bringing novel material options [4,5]. Here, we systematically investigate the charge-to-spin conversion efficiency θH in X/Pt/CoFeB/MgO multilayers (X = Ta, Cr, W, Ru are chosen due to their predicted large orbital Hall conductivity [6]). We report an enhanced θH of 0.168 in Ta/Pt/CoFeB and θH of 0.1 in Ru/Pt/CoFeB compared to the Pt, attributed to the large orbital Hall effect (OHE). The quantified θH for Cr/Pt and W/Pt SOT bilayers is smaller than that of Pt(10) when the thickness of X and Pt layers are fixed to 8 nm/2 nm, as shown in Fig. 1, because of the orbital current may not saturate in the limited thickness [7,8]. We also show that the Ta/Pt bilayer can achieve efficient current-induced magnetization switching in Ta(8-12 nm)/Pt(2 nm)/Co(0.65 nm) heterostructures with perpendicular magnetic anisotropy. The switching current density Jc for the device with tTa = 11.7 nm is only ~1.3×1011 A/m2, as shown in Fig. 2. For the switching current Ic, it firstly increases with tTa because the SOT channel becomes thicker, and then decreases because of the increased θH. Consequently, the Ic for Ta(8)/Pt(2) and Ta(12)/Pt(2) remains nearly the same, thus helping solve the etching-stop issue. Further, the Hall-bar devices were post-annealed at 400°C for 30 minutes. The SOT-induced switching remains robust, and the Jc is just slightly increased though the anisotropic field is substantially enhanced to over 0.9 T, which is of practical interest for BEOL-compatible SOT-MRAM. Our results shed light on the development of high-performance SOT-MRAM leveraging the freedom of orbital angular momentum.References: 1. Z. Guo, et al., Proceedings of the IEEE, Vol. 109, p. 1398-1417 (2021) 2. Y. Yao, et al., Materials Futures, Vol. 2, p. 032302 (2023) 3. C. Pai, et al., Applied Physics Letters, Vol. 101, p. 122404 (2012) 4. D. Lee, et al., Nature Communications, Vol. 12, p. 6710 (2021) 5. Y. Choi, et al., Nature, Vol. 619, p. 52-56 (2023) 6. L. Salemi, P. Oppeneer, Physical Review Materials, Vol. 6, p. 095001 (2022) 7. H. Hayashi, et al., Communications Physics, Vol. 6, p. 32 (2023) 8. S. Lee, et al., Communications Physics, Vol. 4, p. 234 (2021)
Spin-orbit torque (SOT), as a promising writing method for magnetic random-access memory (MRAM), has garnered widespread interest for over a decade [1,2]. Heavy metals, such as β-W, have been broadly adopted as spin current sources, but suffer from a drastic drop of charge-to-spin conversion efficiency at a limited thickness [3]. This poses challenges for simultaneously satisfying SOT efficiency, etching-stop margins, and back-end-of-line (BEOL) compatibility. Orbitronics brings new opportunities for addressing these issues by bringing novel material options [4,5]. Here, we systematically investigate the charge-to-spin conversion efficiency θH in X/Pt/CoFeB/MgO multilayers (X = Ta, Cr, W, Ru are chosen due to their predicted large orbital Hall conductivity [6]). We report an enhanced θH of 0.168 in Ta/Pt/CoFeB and θH of 0.1 in Ru/Pt/CoFeB compared to the Pt, attributed to the large orbital Hall effect (OHE). The quantified θH for Cr/Pt and W/Pt SOT bilayers is smaller than that of Pt(10) when the thickness of X and Pt layers are fixed to 8 nm/2 nm, as shown in Fig. 1, because of the orbital current may not saturate in the limited thickness [7,8]. We also show that the Ta/Pt bilayer can achieve efficient current-induced magnetization switching in Ta(8-12 nm)/Pt(2 nm)/Co(0.65 nm) heterostructures with perpendicular magnetic anisotropy. The switching current density Jc for the device with tTa = 11.7 nm is only ~1.3×1011 A/m2, as shown in Fig. 2. For the switching current Ic, it firstly increases with tTa because the SOT channel becomes thicker, and then decreases because of the increased θH. Consequently, the Ic for Ta(8)/Pt(2) and Ta(12)/Pt(2) remains nearly the same, thus helping solve the etching-stop issue. Further, the Hall-bar devices were post-annealed at 400°C for 30 minutes. The SOT-induced switching remains robust, and the Jc is just slightly increased though the anisotropic field is substantially enhanced to over 0.9 T, which is of practical interest for BEOL-compatible SOT-MRAM. Our results shed light on the development of high-performance SOT-MRAM leveraging the freedom of orbital angular momentum.References: 1. Z. Guo, et al., Proceedings of the IEEE, Vol. 109, p. 1398-1417 (2021) 2. Y. Yao, et al., Materials Futures, Vol. 2, p. 032302 (2023) 3. C. Pai, et al., Applied Physics Letters, Vol. 101, p. 122404 (2012) 4. D. Lee, et al., Nature Communications, Vol. 12, p. 6710 (2021) 5. Y. Choi, et al., Nature, Vol. 619, p. 52-56 (2023) 6. L. Salemi, P. Oppeneer, Physical Review Materials, Vol. 6, p. 095001 (2022) 7. H. Hayashi, et al., Communications Physics, Vol. 6, p. 32 (2023) 8. S. Lee, et al., Communications Physics, Vol. 4, p. 234 (2021)