Spin-orbit torque switching from spin-momentum locked surface states of amorphous BiSe
ORAL
Abstract
Given the recent observation of spin-momentum locked surface states in amorphous Bi2Se3, the textbook three dimensional topological insulator in its crystalline form, it is natural to couple these states to a ferromagnetic layer to manipulate the magnetization for use in potential spintronic applications.
Due to the spin-momentum locked surface states, an electrical current flowing posseses a net spin-polarization, which we use to switch an adjacent ferromagnetic layer using spin-orbit torque. We grow heterostructures of amorphous Bi2Se3 on top of a sputtered Ta/Co/Pt magnetic layer stack, which has perpendicular magnetic anisotropy. We investigate the spin-orbit torque efficiency of the Bi2Se3 by using standard harmonic hall and hysteresis loop shift measurements with devices in Hall-cross geometry. Finally, we are exploring the ultrafast magnetization dynamics by patterning the material stack and depositing an Auston switch on a LT-GaAs substrate, that allows the generation of ps-current pulses, while the magnetic response is observed using time resolved MOKE measurements.
For amorphous Bi2Se3-thicknesses <10nm we find a spin Hall angle that is larger compared to those of conventional heavy metals. The spin-orbit torque efficiency is furthermore decreasing for increasing Bi2Se3-thickness, indicating a dominant contribution of the spin-momentum locked surface states.
Our results have important consequences to technological applications since the growth conditions of amorphous Bi2Se3 are much less stringent than its crystalline counterpart.
Due to the spin-momentum locked surface states, an electrical current flowing posseses a net spin-polarization, which we use to switch an adjacent ferromagnetic layer using spin-orbit torque. We grow heterostructures of amorphous Bi2Se3 on top of a sputtered Ta/Co/Pt magnetic layer stack, which has perpendicular magnetic anisotropy. We investigate the spin-orbit torque efficiency of the Bi2Se3 by using standard harmonic hall and hysteresis loop shift measurements with devices in Hall-cross geometry. Finally, we are exploring the ultrafast magnetization dynamics by patterning the material stack and depositing an Auston switch on a LT-GaAs substrate, that allows the generation of ps-current pulses, while the magnetic response is observed using time resolved MOKE measurements.
For amorphous Bi2Se3-thicknesses <10nm we find a spin Hall angle that is larger compared to those of conventional heavy metals. The spin-orbit torque efficiency is furthermore decreasing for increasing Bi2Se3-thickness, indicating a dominant contribution of the spin-momentum locked surface states.
Our results have important consequences to technological applications since the growth conditions of amorphous Bi2Se3 are much less stringent than its crystalline counterpart.
–
Publication: Paul Corbae et al. "Evidence for topological surface states in amorphous Bi2Se3". In: arXiv preprint arXiv:1910.13412 (2019). doi: https://doi.org/10.48550/arXiv.1910.13412.
Presenters
-
Felix J Kohr
University of California, Berkeley
Authors
-
Felix J Kohr
University of California, Berkeley
-
Paul Corbae
University of California, Berkeley, University of California, Santa Barbara
-
Debanjan Polley
University of California, Berkeley, Lawrence Berkeley National Laboratory
-
Frances Hellman
University of California, Berkeley