Spin transfer switching and spin polarization in magnetic tunnel junctions with MgO and AlO x barriers

We present spin transfer switching results for MgO based magnetic tunneling junctions (MTJs) with large tunneling magnetoresistance (TMR) ratio of up to 150% and low intrinsic switching current density of 2 - 3 × 10 6 A ∕ cm 2 . The switching data are compared to those obtained on similar MTJ nanostructures with AlO x barrier. It is observed that the switching current density for MgO based MTJs is 3 to 4 times smaller than that for AlO x based MTJs, and that can be attributed to higher tunneling spin polarization (TSP) in MgO based MTJs. In addition, we report a qualitative study of TSP for a set of samples, ranging from 0.22 for AlO x to 0.46 for MgO based MTJs, and that shows the TSP (at finite bias) responsible for the current-driven magnetization switching is suppressed as compared to zero-bias tunneling spin polarization determined from TMR.