Spin-orbit torque switching in MgO/CoFeB/Ta/CoFeB/MgO heterostructures with a critical current density of 10(5)A/cm(2)

摘要

Spin-orbit torque-induced magnetization switching in heavy metal/ferromagnetic metal/oxide heterostructures has been extensively studied. However, thus far, the critical current density for magnetization switching in these systems is at least similar to 10(6)A/cm(2). Here, we investigate the spin-orbit torque switching in a substrate/MgO/CoFeB/Ta/CoFeB/MgO structure where the upper CoFeB layer exhibits a strong perpendicular magnetic anisotropy in contrast to the relatively weak perpendicular anisotropy in the lower CoFeB layer. By varying the thickness of Ta, we observe that the critical current required for switching differs markedly. Specifically, for the sample with a 3-nm-thick Ta layer, with an external field of 100Oe applied along the current direction to break the symmetry, the critical current density is similar to 2 x 10(5)A/cm(2). This could be ascribed to the minimum coercivity and perpendicular anisotropic field in the sample with a 3-nm-thick Ta layer. (C) 2017 The Japan Society of Applied Physics