Field-free Spin–Orbit\nTorque Perpendicular\nMagnetization Switching Induced by Metallic Multilayers

The realization of the all-electrical manipulation of\nperpendicular\nmagnetization switching is essential for next-generation information\nstorage technologies and spintronic devices. Current-induced spin–orbit\ntorque (SOT) has attracted tremendous research interest. However,\nthis approach usually relies on external magnetic field to achieve\ndeterministic switching, which greatly limits SOT devices moving toward\npractical applications. Here, we report the measurement of SOT from\nthe [Pt/Au] multilayer with composition gradient along the thickness\ndirection. The multilayer exhibits a much larger SOT efficiency than\npure Pt, and current-induced field-free magnetization switching has\nbeen realized in Co/[Pt/Au] heterostructures. Anomalous Hall resistance\nloop shift measurements indicate that the [Pt/Au] multilayer can produce\nspin current with <i>z</i>-direction polarization. Moreover,\nthe results of the control experiments show that the Pt/Au interface\nis the primary cause of the <i>z</i>-direction polarized\nspin current for triggering field-free switching, whereas the compositional\ngradient effect is peripheral. We speculate that the field-free switching\noriginates from the synergetic interface effect and Dzyaloshinskii–Moriya\ninteraction. Our work not only paves the way for SOT devices toward\npractical application but also provides novel insights into the mechanisms\ngoverning current-induced deterministic perpendicular magnetization\nswitching.