Study of the bulk and interfacial origin of orbital torque in Co/Cu/ HfO2 heterostructure

초록

Orbital torque (OT) has recently emerged as a key mechanism for magnetization control in light metals with weak spin orbit couplings. OT is generally understood to originate from two distinct source, the bulk orbital Hall effect (OHE) and the interfacial orbital Rashba-Edelstein effect (OREE) which have typically been considered separately and their relative contributions to torque generation have remained unclear. In this work, we investigate Cu thickness of OTs and suggest qualitative evidence that both OHE and OREE. Furthermore, X-ray absorption spectroscopy reveals the presence of a Cu/CuOx near the Cu/HfO2 interface, providing the necessary structural condition for OREE. These results demonstrate that OT in Cu is not governed by a single mechanism but instead arises from a cooperative interplay between interfacial and bulk orbital processes. Our findings establish Cu as a robust platform for orbital current modulation and offer new insight into the origin of OT in light metals.

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