Naturally oxidized copper (${\mathrm{CuO}}_x$) was cited as an exceptionally strong orbital current source despite the keen debate over the concept of orbital current. Here, we report unambiguous experimental evidence for the absence of a detectable orbital current torque in the Fe/Pt/${\mathrm{CuO}}_x$ trilayers. Using a magnetic metal detector of Fe thin film with a negligible self-induced torque, the dampinglike torque due to Pt/${\mathrm{CuO}}_x$ bilayers is clarified to entirely arise from the spin Hall spin current of the Pt. As the Pt thickness increases, the torque for Fe/Pt/${\mathrm{CuO}}_x$ and Fe/Pt/MgO increases coherently and monotonically, as exactly expected from the spin Hall effect of Pt and the drift-diffusion model of spin angular momentum. These findings suggest little generation of orbital current from the Pt/${\mathrm{CuO}}_x$ interface.

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• Spin Hall effect
• Spin-orbit torque
• Device fabrication
• Ferromagnets
• Thin films
• Energy-dispersive x-ray spectroscopy
• Magnetization measurements
• Sputtering