Anisotropic Spin-Orbit Torque through Crystal-Orientation Engineering in Epitaxial Pt

One of the main objectives of spintronics is to provide power-efficient switching of magnetic layers through electrical means, and in order to achieve this goal, alternate material systems with enhanced spin-orbit torque (SOT) must be engineered. In this work we provide evidence of anisotropy in the SOT and spin Hall effect (SHE) in epitaxial Pt(110) grown on MgO(110) single-crystal substrates, and find that the spin Hall angle and the dampinglike torque are 20% larger when current is applied along the [001] crystallographic direction as compared to [11¯0], leading to an equivalent reduction in switching current density along [001]. The anisotropy in SOT is attributed to the bulk contributions of the SHE in the Pt layer through its anisotropic resistance in this specific orientation. Measurements additionally suggest that the Rashba-Edelstein effect at the Pt/Ti interface due to the Pt(110) surface has a non-negligible effect on the spin diffusion length and SOT. By providing experimental evidence of the crystal orientation dependence of SOT-induced magnetization switching, this work helps to establish a path for energy-efficient magnetization switching through the alignment of devices with crystallographic directions of enhanced SOT generation.