Thermal-annealing-induced Symmetry Breaking Enables Field-Free Spin-Orbit-torque Switching of a Perpendicular Ferrimagnet

Current-induced spin-orbit torque (SOT) offers a promising approach for manipulating perpendicular magnetization in spintronic devices, enabling low-power and ultrafast applications. However, deterministic SOT switching typically requires an external in-plane magnetic field to break symmetry, complicating high-density device integration. Here, we demonstrate field-free SOT switching in the perpendicular ferrimagnet CoGd by inducting tilted magnetic anisotropy (TMA) via thermal annealing under an inplane magnetic field. The TMA's tilt angle is tunable by adjusting the annealing field strength, allowing deterministic switching when the in-plane TMA component aligns with the spin-polarization direction. This method leverages the low stray field, ultrafast spin dynamics, and high operation frequencies of ferrimagnet, offering a scalable solution for advanced spintronic devices.