Large orbital torque with concurrent mitigation of magnetic damping in titanium/rare-earth lutetium metallic heterostructures

Improving the spin–orbit torque efficiency is essential for achieving high-performance and low-power spintronic devices. However, enhancing torque efficiency inevitably intensifies spin pumping, which leads to an increase in the magnetic damping of the system. In this work, we demonstrate that Ti/rare-earth Lu/Permalloy (Py) metallic heterostructures generate large orbital torque without significantly increasing damping. Utilizing the spin-torque ferromagnetic resonance technique, the torque efficiency is measured to be approximately −0.228, which is comparable to that of the Ti/Pt/Py system. Furthermore, while delivering substantial orbital torque, the Gilbert damping constant of the Ti/Lu/Py metallic heterostructure increases by less than 5% compared to that of Ti/Py. In contrast, the damping in Ti/Pt/Py increases by approximately 82.6%. This difference arises because Lu exhibits an extremely small inverse spin Hall effect. Our findings indicate that light-metal/rare-earth Lu heterostructures hold great promise for realizing orbitronic devices that achieve both high efficiency and low damping.