Comprehensive Study of the Current-Induced Spin–Orbit Torque Perpendicular Effective Field in Asymmetric Multilayers
Baoshan Cui,
Zengtai Zhu,
Chuangwen Wu,
Xiaobin Guo,
Zhuyang Nie,
Hao Wu,
Tengyu Guo,
Peng Chen,
Dongfeng Zheng,
Tian Yu,
Li Xi,
Zhongming Zeng,
Shiheng Liang,
Guangyu Zhang,
Guoqiang Yu,
Kang L. Wang
Affiliations
Baoshan Cui
Songshan Lake Materials Laboratory, Dongguan 523808, China
Zengtai Zhu
Songshan Lake Materials Laboratory, Dongguan 523808, China
Chuangwen Wu
Songshan Lake Materials Laboratory, Dongguan 523808, China
Xiaobin Guo
School of Physics & Optoelectric Engineering, Guangdong University of Technology, Guangzhou 510006, China
Zhuyang Nie
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Hao Wu
Songshan Lake Materials Laboratory, Dongguan 523808, China
Tengyu Guo
Songshan Lake Materials Laboratory, Dongguan 523808, China
Peng Chen
Songshan Lake Materials Laboratory, Dongguan 523808, China
Dongfeng Zheng
Songshan Lake Materials Laboratory, Dongguan 523808, China
Tian Yu
College of Physics, Sichuan University, Chengdu 610064, China
Li Xi
Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China
Zhongming Zeng
Nanofabrication Facility, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China
Shiheng Liang
Faculty of Physics and Electronic Science, Hubei University, Wuhan 430062, China
Guangyu Zhang
Songshan Lake Materials Laboratory, Dongguan 523808, China
Guoqiang Yu
Songshan Lake Materials Laboratory, Dongguan 523808, China
Kang L. Wang
Department of Electrical Engineering, University of California, Los Angeles, CA 90095, USA
The spin–orbit torques (SOTs) in the heavy metal (HM)/ferromagnetic metal (FM) structure hold promise for next-generation low-power and high-density spintronic memory and logic applications. For the SOT switching of a perpendicular magnetization, an external magnetic field is inevitable for breaking the mirror symmetry, which is not practical for high-density nanoelectronics applications. In this work, we study the current-induced field-free SOT switching and SOT perpendicular effective field (Hzeff) in a variety of laterally asymmetric multilayers, where the asymmetry is introduced by growing the FM layer in a wedge shape. We show that the design of structural asymmetry by wedging the FM layer is a universal scheme for realizing field-free SOT switching. Moreover, by comparing the FM layer thickness dependence of (Hzeff) in different samples, we show that the efficiency (β =Hzeff/J, J is the current density) is sensitive to the HM/FM interface and the FM layer thickness. The sign of β for thin FM thicknesses is related to the spin Hall angle (θSH) of the HM layer attached to the FM layer. β changes its sign with the thickness of the FM layer increasing, which may be caused by the thickness dependence of the work function of FM. These results show the possibility of engineering the deterministic field-free switching by combining the symmetry breaking and the materials design of the HM/FM interface.
