Revelation of Pattern formation in Single Ferromagnetic CoFeB Film by Using the Giant Spin Hall Spin Torque

摘要

Current induced torque enables magnetization switching via a spin transfer torque mechanism, viz., the spin angular momentum of conduction electrons was transferred to the local magnetization. This phenomenon exhibits an important impact on the recording technology, since the opposite (upward/downward) magnetization configurations can be assigned as "0" and "1", respectively, thus leading information to be encoded/decoded electrically [1]. Examples of which can be extensively found, such as magnetic domain wall logics and spin transfer torque random access memory (STT-RAM) in which the magnetization states can be reconfigured via a so called spin transfer torque mechanism [2]. However, the major obstacle is to increase the energy efficiency by lowering the switching current (10~(10-12) A/m~2) which co-introduces Joule heating, Oersted fields, etc. Exploring novel mechanisms and materials therefore, forms as the dominant trend for which could overcome the above barrier, such as systems with perpendicular magnetization anisotropics, and spin textures (including (anti)vortices, skyrmion). Amongst them, a recent progress have demonstrated the electrical control of magnetic memory and nonvolatile spin logics through in-plane current injection - Spin torque switching with the Giant spin Hall effect in a perpendicularly magnetized Ta/CoFeB/MgO/Ta heterostructure. Owing to the presence of giant spin Hall angle (θsh ≈ 0.12 - 0.15) of the high-resistivity β-tantalum film, the electrical current flows in β-Ta thin film hence produces an abrupt switching of the adjacent ferromagnetic CoFeB layer through the spin Hall spin torque [3].