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.