Hard axis magnetic field dependence on current-induced magnetization switching in MgO-based magnetic tunnel junctions : Topical issue on new trends in spin transfer physics

We conducted a detailed study of hard axis magnetic field (Hhard) dependence on current-induced magnetization switching (CIMS) in MgO-based magnetic tunnel junctions (MTJs) with various junction sizes and various uniaxial anisotropy fields. The decreases in critical current density (Jc) and the intrinsic critical current density (Jc0) estimated from the pulse duration dependence on Jc in CIMS are observed when applying Hhard for all MTJs. The decrease in energy barrier of CIMS is also observed except for the largest sample. These results indicate that the reduction of Jc is attributable to both the increase of spin-transfer efficiency and the decrease in energy barrier in the case of applying Hhard. The Jc0 decreases with increase in the mutual angle between the direction of magnetization and the easy axis (θf), which is consistent with the theoretical prediction proposed by Slonczewski. The degree of the reduction of Jc0 for the same value of Hhard decreases with decreasing size of MTJs. This behavior is considered to be related to not only decrease in Of due to the increase in anisotropy field in MTJs, but also to the increase in the variance of the initial angle of magnetization due to the thermally activated magnon excitation. The stable switching endurance related to CIMS was observed in a wide range of MTJ sizes when applying Hhard. Moreover, we proposed a new architecture and a new switching method considering write disturbance. These results would be useful for application to spin memory and other spin-electronic devices.