Strong higher-order angular dependence of spin-orbit torque in W/CoFeB bilayer

被引:7
作者
Park, Eun-Sang [1 ,2 ]
Lee, Dong-Kyu [3 ]
Xue, Fei [4 ,5 ]
Min, Byoung-Chul [2 ]
Koo, Hyun Cheol [1 ,2 ]
Haney, Paul M. [4 ]
Kim, Kyoung-Whan [2 ]
Lee, Kyung-Jin [6 ]
机构
[1] Korea Univ, KU KIST Grad Sch Converging Sci & Technol, Seoul 02841, South Korea
[2] Korea Inst Sci & Technol, Ctr Spintron, Seoul 02792, South Korea
[3] Korea Univ, Dept Mat Sci & Engn, Seoul 02841, South Korea
[4] NIST, Phys Measurement Lab, Gaithersburg, MD 20899 USA
[5] Univ Alabama Birmingham, Dept Phys, Birmingham, AL 35294 USA
[6] Korea Adv Inst Sci & Technol KAIST, Dept Phys, Daejeon 34141, South Korea
基金
新加坡国家研究基金会;
关键词
CURRENT-DRIVEN DYNAMICS; PERPENDICULAR MAGNETIZATION; LOW-POWER; SYMMETRY;
D O I
10.1103/PhysRevB.107.064411
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
The symmetry of normal metal/ferromagnet bilayers allows spin-orbit torques (SOTs) to simultaneously have two distinct angular dependences on the magnetization direction m. The most well-studied forms of SOT consist of the conventional fieldlike and dampinglike torques, which we label as "lowest-order" SOT. There are additional SOT forms associated with spin polarization different from that of the lowest-order SOT, and which contain an extra factor of m dependence. We label these as "higher-order" SOT. Understanding SOT-driven magnetization dynamics requires detailed information about the full angular dependence. In this paper, we measure both the lowest-order and higher-order angular dependences of SOTs in three types of bilayers, Pt/Co, Ta/CoFeB, and W/CoFeB, using harmonic Hall measurements. It is found that the higher-order SOT is negligible for Pt/Co and Ta/CoFeB, whereas it is dominant over the lowest-order one for W/CoFeB. Macrospin simulations show that the higher-order SOT can significantly affect the magnetization dynamics, which is qualitatively in line with SOT-induced switching experiments.
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页数:9
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