Ultrastrong Unconventional Spin Current via Noncollinear Spin-Orbit Filtering

Spin-orbitronics harnesses spin-orbit coupling to generate pure spin currents for energy-efficient information processing, particularly through the spin-orbit torque (SOT) that drives magnetization switching. However, achieving efficient SOT switching of perpendicular magnetization, which is crucial for high-density applications, remains challenging due to the difficulty in generating spin currents with both high conductivity and out-of-plane polarization in conventional, industry-compatible spin sources, such as heavy metals. Here, we overcome this limitation by demonstrating a noncollinear spin-orbit filtering effect at the surface termination of conventional spin sources. This effect selectively transmits electrons based on the relative alignment between their spin vectors and the interfacial Rashba-Edelstein field. By implementing this strategy in platinum (Pt) epitaxial films with ( n 10 ) orientations ( n = 2 – 4 ), we achieve exceptionally strong z -polarized spin currents. The resulting out-of-plane spin Hall conductivity reaches a record value of 0.75 × 10 5 ( ħ / 2 e ) Ω − 1 m − 1 , surpassing all previous approaches, and enables robust field-free switching of perpendicular magnetization. Notably, the field-free switching is precisely controlled by engineering the crystal point group symmetry from C 1 v to C 4 v . Our work establishes a general framework for transforming conventional high-symmetry materials into out-of-plane spin sources, paving the way for highly efficient and scalable spintronic memory technology.