Orbital torque originating from orbital Hall effect in Zr

We investigate current-induced torques generated by Zr. We show that the generation efficiency of the current-induced torque increases with increasing the thickness of the Zr layer in Ni81Fe19/Zr and Ni/Zr bilayers, which indicates that the observed current-induced torque originates from the bulk of the Zr layer. We find that the sign of the current-induced torques is opposite to that expected from the spin Hall effect but is consistent with that expected from the orbital Hall effect in the Zr layer. Furthermore, we find that the torque efficiency increases with increasing the thickness of the ferromagnetic layer, which is consistent with the prediction of long-range orbital transport in ferromagnets. These observations demonstrate that the orbital Hall effect in the Zr layer is the main source of the current-induced torque. This finding highlights the important role of orbital transport in generating current-induced torques, advancing the understanding of angular momentum dynamics in solid-state devices with 4d transition metals.