Controllable field-free switching of perpendicular magnetization through bulk spin-orbit torque in symmetry-broken ferromagnetic films

TLDR

Field‑free manipulation of perpendicular magnetization is essential for ultralow‑power spintronic devices, yet a centrosymmetric single‑layer ferromagnetic film cannot be switched directly by electrical current alone. The study demonstrates repeatable bulk spin‑orbit torque switching of perpendicularly magnetized CoPt single‑layer films by introducing a thickness‑direction composition gradient that breaks inversion symmetry. Bulk SOT switching is achieved by a thickness‑direction composition gradient that breaks inversion symmetry in the CoPt alloy single‑layer films. Experimental results show that bulk SOT‑induced effective fields drive domain‑wall motion and magnetization switching, that field‑free perpendicular switching polarity can be reversibly controlled in IrMn/Co/Ru/CoPt heterojunctions via exchange bias and interlayer coupling, and that this composition‑gradient approach offers a promising strategy for energy‑efficient memory and logic devices.

Abstract

Abstract Programmable magnetic field-free manipulation of perpendicular magnetization switching is essential for the development of ultralow-power spintronic devices. However, the magnetization in a centrosymmetric single-layer ferromagnetic film cannot be switched directly by passing an electrical current in itself. Here, we demonstrate a repeatable bulk spin-orbit torque (SOT) switching of the perpendicularly magnetized CoPt alloy single-layer films by introducing a composition gradient in the thickness direction to break the inversion symmetry. Experimental results reveal that the bulk SOT-induced effective field on the domain walls leads to the domain walls motion and magnetization switching. Moreover, magnetic field-free perpendicular magnetization switching caused by SOT and its switching polarity (clockwise or counterclockwise) can be reversibly controlled in the IrMn/Co/Ru/CoPt heterojunctions based on the exchange bias and interlayer exchange coupling. This unique composition gradient approach accompanied with electrically controllable SOT magnetization switching provides a promising strategy to access energy-efficient control of memory and logic devices.