Giant Orbital-to-Spin Conversion for Efficient Current-Induced Magnetization Switching of Ferrimagnetic Insulator

It has long been believed that the attachment of twoheavy metalssuch as Ta and Pt with opposite spin Hall angles results in a weakenednet torque generation efficiency in magnetization switching devices.Here, we report a giant orbital-to-spin conversion in Ta/Pt/Tm3Fe5O12 (TmIG) heterostructures. We showthat the torque generation efficiency is enhanced by an order of magnitudein the Ta/Pt/TmIG trilayer compared to that in the Pt/TmIG bilayer.This enhancement is further evidenced by the fact that the criticalcurrent density for the magnetization switching of the Ta/Pt/TmIGis an order of magnitude smaller than that of the Pt/TmIG. It is foundthat the orbital current generated from Ta through the orbital Halleffect (OHE) is converted to the spin current in the interior of Pt.Our discovery offers an extraordinary approach to enhance the torquegeneration for magnetization switching of insulators and providesan important piece of information for orbitronics.