Mitigation of Gilbert Damping in the CoFe/CuO<sub><i>x</i></sub> Orbital Torque System

Charge-spin\ninterconversion processes underpin the generation of\nspin–orbit torques in magnetic/nonmagnetic bilayers. However,\nefficient sources of spin currents such as 5<i>d</i> metals\nare also efficient spin sinks, resulting in a large increase of magnetic\ndamping. Here we show that a partially oxidized 3<i>d</i> metal can generate a strong orbital torque without a significant\nincrease in damping. Measurements of the torque efficiency ξ\nand Gilbert damping α in CoFe/CuO<sub><i>x</i></sub> and CoFe/Pt indicate that ξ is comparable in the two systems.\nThe increase in damping relative to a single CoFe layer is Δα\n< 0.002 in CoFe/CuOx and Δα ≈ 0.005–0.02\nin CoFe/Pt, depending on CoFe thickness. We ascribe the nonreciprocal\nrelationship between Δα and ξ in CoFe/CuO<sub><i>x</i></sub> to the small orbital–spin current ratio generated\nby magnetic resonance in CoFe and the lack of an efficient spin sink\nin CuO<sub><i>x</i></sub>. Our findings provide new perspectives\non the efficient excitation of magnetization dynamics via the orbital\ntorque.