Field-Free Spin–Orbit Torque Magnetization Switching in a Single-Phase Ferromagnetic and Spin Hall Oxide

Current-induced spin–orbit torque (SOT) offers substantial promise for the development of low-power, nonvolatile magnetic memory. Recently, a single-phase material concurrently exhibiting magnetism and the spin Hall effect has emerged as a scientifically and technologically interesting platform for realizing efficient and compact SOT systems. Here, we demonstrate external-magnetic-field-free switching of perpendicular magnetization in a single-phase ferromagnetic and spin Hall oxide SrRuO₃. We delicately altered the local lattices of the top and bottom surface layers of SrRuO₃, while retaining a quasi-homogeneous, single-crystalline nature of the SrRuO₃ bulk. This leads to unbalanced spin Hall effects between the top and bottom layers, enabling net SOT performance within single-layer ferromagnetic SrRuO₃. Notably, our SrRuO₃ exhibits the highest SOT efficiency and lowest power consumption among all known single-layer systems under field-free conditions. Our method of artificially manipulating the local atomic structures will pave the way for advances in spin-orbitronics and the exploration of new SOT materials.