Manipulation of magnetization by electric-current-induced spin-orbit torque (SOT) is of great importance for next generation of magnetic memory and logic because of its merits in energy-efficient and high-speed operation. Implement of SOT in spintronics devices made of metallic multilayers requires both large spin Hall angle and high conductivity (i.e. high spin Hall conductivity) in a material. Compared with the conventional heavy metal like Pt, W etc., two-dimensional transition metal dichalcogenides (TMDs) are appealing because of their tunability in phase, symmetry, conductivity, spin-orbit coupling and non-trivial energy band topology. It has been emerged as a new platform for studying the interplay between different degrees of freedom like charge and spin (or pseudospin). Although numerous reports revealed the relatively large spin Hall angle in TMDs including MoS₂ and WTe₂ etc., there are two crucial issues that need to be solved before application: the relatively low conductivity and the difficulty in controllably fabricating thin films in a large scale. Using high conductive Dirac semimetal with spin-momentum locking in its topological surface states might be a solution, however, studying of SOT in such system is still missing.

Recently, Dr. Hongjun Xu, Prof. Guoqaing Yu and Prof. Xiufeng Han from the M02 group at the Institute of Physics, Chinese Academy of Sciences, has successfully fabricated large-area, high quality PtTe₂ thin films with controllable thicknesses and study the SOT in this type-II Dirac semimetal material for the first time. Learning from the case of PtSe₂, uniform and homogenous [001]-oriented PtTe₂ thin films are transformed from Pt thin films by annealing them in tellurium vapor. Similar to the results of single-crystal PtTe₂ nano flakes, the PtTe₂ thin films are highly conductive at room temperature (~ 10⁶ S/m). Because of their stability in ambient condition, the as-grown PtTe₂ thin films can be transferred into another sputtering system for making spintronics stacks. After a systematic studying of SOT in the PtTe₂/Py stacks with the ST-FMR method, large SOT efficiency was found: for the case of 5 nm PtTe₂ the corresponding spin Hall angle is around 0.09-0.15 which is 1.5-2 times large than the value in the control sample of 4 nm Pt. A nonmonotonic behavior in the thickness dependence of SOT efficiency implies that the SOT in PtTe₂ might originate from two different sources including bulk and surface contributions. A large spin Hall conductivity (0.2-1.6 × 10⁵ ℏ/2e Ω^-1m^-1) is established in PtTe₂ which is the largest one among TMDs reported so far and even comparable to the values of Bi₂Se₃, a representative topological insulator. Further work in perpendicular magnetic moment switching confirmed the higher efficiency of charge-spin conversion in PtTe₂ than Pt. It suggests that PtTe₂ and Dirac semimetal is compelling for low-power SOT devices and other applications related to charge-spin interconversion. This work paves the way for employing PtTe₂-like TMDs for wafer-scale spintronic device applications [H. J. Xu, J. W. Wei, H. G. Zhou, J. F. Feng, T. Xu, H. F. Du, C. L. He, Y. Huang, J. W. Zhang, Y. Z. Liu, H.-C. Wu, C. Y. Guo, X. Wang, Y. Guang, H. X. Wei, Y. Peng, W. J. Jiang, G. Q. Yu,* and X. F. Han, High Spin Hall Conductivity in Large-Area Type-II Dirac Semimetal PtTe₂, Adv. Mater. 10 (2020) 2000513]。.

The work was supported by the Ministry of Science and Technology of China [No. 2017YFA0206200], the National Science Foundation [NSFC Nos. 11874409, 11674373, 51801087, 11804380], and the Chinese Academy of Sciences [QYZDJ-SSW-SLH016].

Article link：https://onlinelibrary.wiley.com/doi/full/10.1002/adma.202000513?af=R