Collinear Spin Current Induced by Artificial Modulation of Interfacial Symmetry

Current induced spin-orbit torque (SOT) manipulation of magnetization is pivotal in spintronic devices. However, its application for perpendicular magnetic anisotropy magnets, crucial for high-density storage and memory devices, remains nondeterministic and inefficient. Here, a highly efficient approach is demonstrated to generate collinear spin currents by artificial modulation of interfacial symmetry, achieving 100% current-induced field-free SOT switching in CoFeB multilayers with perpendicular magnetization on stepped Al₂O₃ substrates. This field-free switching is primarily driven by the out-of-plane anti-damping SOT generated by the planar spin Hall effect (PSHE), resulting from reduced interface symmetry due to orientation-determined steps. Microscopic theoretical analysis confirms the presence and significance of PSHE in this process. Notably, this method for generating out-of-plane spin polarization along the collinear direction of the spin-current with artificial modulation of interfacial symmetry, overcomes inherent material symmetry constraints. These findings provide a promising avenue for universal control of spin-orbit torque, addressing challenges associated with low crystal symmetry and highlighting its great potential to advance the development of energy-efficient spintronic devices technology.