Enhanced Magnetization Switching Efficiency via Orbital-Current-Induced Torque in Ti/Ta (Pt)/CoFeB/MgO Structures

초록

Spin-orbit torque (SOT), arising from spin currents induced by the spin Hall effect, enables the efficient electrical switching of magnetization. However, for practical application in spintronic devices, the switching current must be reduced. Recent studies have shown that the orbital Hall conductivity is much larger than the spin Hall conductivity in various transition metals, prompting investigations to exploit it to enhance SOT switching efficiency. Despite extensive research on orbital currents, a demonstration showing that orbital-current-induced torque (OT) surpassed conventional SOT has yet to be reported. In this Article, it is demonstrated that introducing Ti as an orbital current source significantly reduces the switching current of perpendicularly magnetized CoFeB. In Ti/Ta (Pt)/CoFeB/MgO structures, the OT originates from orbital currents generated in the Ti and subsequent conversion into spin currents via the thin Ta (Pt) layer. The OT-induced switching current in Ti/Ta (or Pt)/CoFeB/MgO is similar to 25% lower than that of a conventional SOT structure of Ta/CoFeB/MgO. This enhancement was confirmed by harmonic Hall measurements, showing an effective spin Hall angle of 0.060 in the Ti/Ta/CoFeB/MgO structure, exceeding that of the Ta/CoFeB/MgO structure (0.038). These findings pave the way for utilizing orbital currents in the development of energy efficient spintronic devices.

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