Spin-orbit torque magnetometry: methods and figures of merit for spin-orbit torque characterization

Tian-Yue Chen¹, Tsung-Yu Tsai¹, Hsin-I Chan¹, Wei-Bang Liao¹, Neil Murray¹, Chi-Feng Pai^1*

¹Materials Science and Engineering, National Taiwan University, Taipei, Taiwan

* Presenter:Chi-Feng Pai, email:cfpai@ntu.edu.tw

Since the discovery of in-plane current induced spin-orbit torques (SOTs) in heavy metal/ferromagnetic metal bi-layer systems in early 2010’s, the quest for better SOT characterization approaches and measurement techniques has never stopped. One of the reasons why SOT-related research has been growing such rapidly is perhaps due to the simplicity of characterization technique and device layout. Using one of the most popular approaches, harmonic voltage measurement, which was proposed by Pi et. al. in 2010 [1] and later refined by Kim et. al. in 2013 [2], researchers are allowed to quantify both damping-like and field-like SOTs through an elegant AC signal detection scheme using simple device with Hall-bar geometry. The capability of characterizing SOT efficiency and even observing SOT switching in micron-sized Hall-bar devices has made SOT research more and more popular during the past few years.

However, it is also now clear that the observed SOT switching and SOT-induced dynamics are mostly related to domain nucleation and chiral domain wall propagation in the magnetic heterostructure-of-interest [3], especially in the micron-sized samples with the magnetization not being single domain. This chiral domain wall-related feature actually provides us alternatives for SOT characterization based on domain wall propagation and domain expansion in patterned magnetic heterostructures, such as spin Hall torque magnetometry by Emori et. al. in 2014 [4] and hysteresis loop shift measurement by Pai et. al. in 2016 [5]. In this presentation, I will show that the concept of SOT characterization in patterned, micron-sized samples can be employed to un-patterned samples as well. The possibility of performing SOT characterization using as-prepared films without further fabrication processes will eventually increase the overall SOT research throughput for many researchers in the field of spin-orbitronics [6].

References

[1] U. H. Pi, K. W. Kim, J. Y. Bae, S. C. Lee, Y. J. Cho, K. S. Kim, and S. Seo, Appl. Phys. Lett. 97, 162507 (2010).
[2] J. Kim, J. Sinha, M. Hayashi, M. Yamanouchi, S. Fukami, T. Suzuki, S. Mitani, and H. Ohno, Nat. Mater. 12, 240 (2013).
[3] O. J. Lee, L. Q. Liu, C. F. Pai, Y. Li, H. W. Tseng, P. G. Gowtham, J. P. Park, D. C. Ralph, and R. A. Buhrman, Phys. Rev. B 89, 024418 (2014).
[4] S. Emori, E. Martinez, K. J. Lee, H. W. Lee, U. Bauer, S. M. Ahn, P. Agrawal, D. C. Bono, and G. S. D. Beach, Phys. Rev. B 90, 184427 (2014).
[5] C. F. Pai, M. Mann, A. J. Tan, and G. S. D. Beach, Phys. Rev. B 93, 144409 (2016).
[6] T. Y. Tsai, T. Y. Chen, C. T. Wu, H. I. Chan, and C. F. Pai, Sci. Rep. 8, 5613 (2018).

Keywords: spin-orbit torque, spin-transfer torque, spintronics, MRAM, topological insulator