Enhanced spin-orbit torques in rare-earth Pt/[Co/Ni]2/Co/Tb systems
Wong, Qi Ying
Law, Wai Cheung
Gan, Wei Liang
Lim, Gerard Joseph
Lew, Wen Siang
Date of Issue2019
School of Physical and Mathematical Sciences
We report the enhanced spin-orbit torque (SOT) effect due to the rare-earth metal Tb in a Pt/[Co/Ni]2/Co/Tb multilayer with perpendicular magnetic anisotropy (PMA). Due to the large spin-orbit coupling in Tb, the effective dampinglike efficiency, ξeffDL, is determined to be 0.55 for 9-nm Tb as compared to ξeffDL=0.18 for the reference Pt/[Co/Ni]2/Co/Ta stack. A relatively large effective spin Hall efficiency of Tb, θeffSH,Tb, is determined to be −0.480 for Tbwith a 9-nm thickness through a Hz-biased harmonic measurement. Enhanced magnetization switching efficiency is observed with increasing Tb thickness, affirming the sizable antidamping torque responsible for deterministic switching. Furthermore, due to a more substantial interfacial coupling in Co/Tb interface than in Co/Ta interface, strong angular dependence of the dampinglike and fieldlike terms is, but diminishes with increasing Tb thickness. These results affirm that Tb plays a significant role in tuning the SOT efficiency in these structures as the increased Tb concentration leads to an enhancement of the effective spin Hall angle and switching efficiency.
Physical Review Applied
© 2019 American Physical Society. All rights reserved. This paper was published in Physical Review Applied and is made available with permission of American Physical Society.