Symmetry-reduced topological interface for unleashing a multidirectional spin-orbit torque

Current-induced spin-orbit torque at heavy metal/ferromagnet interfaces plays a critical role in modern spintronics. The challenges in relevant research are to enhance the conversion efficiency and generate unconventional torque components. Here, we propose a simple protocol to meet such demands by engineering symmetrical structures, specifically by a wedge-shaped topological material interface in Bi2Te3/CoFeB heterostructures. The symmetry of the topological interface is manipulated to lead to unconventional emergences of both the out-of-plane and in-plane spin polarizations. Torque measurements show that these polarizations have conversion efficiencies up to 10%, characterized by the nonreciprocal ferromagnetic resonance spectra and the distinctive torque profile. The observed enhancement in the unconventional spin-orbit torque is attributed to the wedge-oriented symmetry reduction of the spin-momentum locking structure of interfacial Dirac fermions. This advance opens avenues for designing geometrically characteristic spintronics devices, demonstrating the potential of using multidirectional spin-orbit torques for forthcoming nanotechnological applications. Spin-orbit coupling offers the possibility to generate, control, and detect spin currents for applications of spin-based information. The authors introduce symmetry-induced engineering of the spin-orbit torque in heterostructures based on ferromagnets and topological materials. These results disclose novel perspectives on non-volatile memories and non-conventional computing.