Thickness and temperature dependence of antiferromagnetic coupling in the Gd/Co double-wedge bilayer
Liang-Wei Lan1*, Aldrin Chang1, Wei-Ming Li2, Swati Kanojia1, Jyun-Syong Jhuang3, Wei-Sheng Chiu3, Chii-bin Wu2, Tzu-Hung Chuang3, Chien-Cheng Kuo1
1Department of Physics, National Sun Yat-sen University, Kaochsiung, Taiwan
2Department of Physics, Chung Yuan Christian University, Taoyuan, Taiwan
3National Synchrotron Radiation Center, Hsinchu, Taiwan
* Presenter:Liang-Wei Lan,
The synthetic antiferromagnetic (SAF) system has provided a platform for studying the field-free domain wall motion, making the transfer of spin-torque much more efficient and lower energy cost[1]. The proven exchange couple torque (ECT) is maximized when the two ferromagnetic layers in SAF are fully compensated [2,3]. A combination of rare-earth (RE) and transition metal (TM) is an appropriate candidate for the SAF system, especially when two elements reveal rich magnetic behaviors, like Co and Gd. Gd shows a more robust ferromagnetic phase but is of much lower Curie temperature, 292 K roughly at room temperature, than Co. A variation of the temperature can tailor the relative magnetic strength of Gd and Co and reach a fully compensated configuration. Additionally, in the ultrathin limit, the films confront the finite size effect [4], providing an alternative for modulating the magnetic strength. This study utilizes the double-wedge design with element-sensitive magnetic microscopy to perform a comprehensive and systematic study to address the mentioned issues. A Gd/Co double-wedge system was made to investigate the evolution of the magnetic domain as a function of ferromagnetic layer thickness. The photoemission electron microscopy with X-ray magnetic circular dichroism (XMCD-PEEM) in TLS-05B2 at NSRRC was used to probe the magnetic domains for Gd and Co in an element-specific manner. The out-of-plane magnetization direction of Co on Pt(111) was observed from 0 to 4 ML at RT. As the thickness of Gd increased, the out-of-plane area of Co varied. The domain image of Gd showed an opposite contrast with Co, which reveals the antiferromagnetic area. The antiferromagnetic domain evolution with the increment of Co and Gd thickness was examined by our experiment.

[1] S. H. Yang, K. S. Ryu, and S. Parkin, Nature Nanotechnology, 10, 221–226 (2015)
[2] J. Finley, and L. Q. Liu, Phys. Rev. Appl. 6, 054001 (2016).
[3] R. Bläsing, T. Ma, S. H. Yang, C. Garg, F. K. Dejene, A. T N’Diaye, G. Chen, K. Liu, and S. S. P. Parkin, Nat Commun 9, 4984 (2018).
[4] E. Weschke, H. Ott, E. Schierle, C. Schüßler-Langeheine, D. V. Vyalikh, G. Kaindl, V. Leiner, M. Ay, T. Schmitte, H. Zabel, and P. J. Jensen, Phys. Rev. Lett., 93, 157204 (2004).

Keywords: synthetic antiferromagnetic, Gd/Co, exchange coupling torque