Abstract
Spin Hall effect, an electric generation of spin current, allows for efficient control of magnetization. Recent theory revealed that orbital Hall effect creates orbital current, which can be much larger than spin-Hall-induced spin current. However, orbital current cannot directly exert a torque on a ferromagnet, requiring a conversion process from orbital current to spin current. Here, we report two effective methods of the conversion through spin-orbit coupling engineering, which allows us to unambiguously demonstrate orbital-current-induced spin torque, or orbital Hall torque. We find that orbital Hall torque is greatly enhanced by introducing either a rare-earth ferromagnet Gd or a Pt interfacial layer with strong spin-orbit coupling in Cr/ferromagnet structures, indicating that the orbital current generated in Cr is efficiently converted into spin current in the Gd or Pt layer. Our results offer a pathway to utilize the orbital current to further enhance the magnetization switching efficiency in spin-orbit-torque-based spintronic devices.
Highlights
Spin Hall effect, an electric generation of spin current, allows for efficient control of magnetization
The orbital Hall effect (OHE) has distinctive features compared to the Spin Hall effect (SHE); first, the OHE originates from momentum-space orbital textures, so it universally occurs in multi-orbital systems regardless of the magnitude of SOC12
To demonstrate the OHE in Cr and associated orbital Hall torque (OHT), we investigate the current-induced spin-torque in Cr/FM heterostructures for two different FMs of coupling of the Gd (Co) and Ni
Summary
Orbital Hall torque generated by orbital current in Cr. To demonstrate the OHE in Cr and associated OHT, we investigate the current-induced spin-torque in Cr/FM heterostructures for two different FMs of Co and Ni. Efficiency[31], ξDLT 1⁄4 ð2e=_ÞðMStFMBDLT=JPtÞ where, MS is the saturation magnetization, tFM is the FM thickness, and JPt is the current density flowing in Pt (Supplementary Note 3), between the Co/Pt and Ni/Pt samples differs by a factor of two. This indicates that interface transmission (Tint) plays a critical role in determining ξDLT in these samples, where the spin current is primarily generated by the SHE in the Pt layer[32]. Note that we analyze the tCr dependence of ξDLT using a methodh of analiyzing the SHE-induced SOT31, ξDLT $
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