Fast Deterministic Bipolar Switching in Orthogonal Spin Torque Devices via the Control of the Relative Spin Polarizations

We model 100 ps pulse switching dynamics of orthogonal spin transfer (OST) devices that employ an out-of-plane polarizer (OPP) and an in-plane polarizer (IPP). Simulation results indicate that increasing the spin polarization ratio, $C_{P\, }= \quad P_{IPP}/P_{OPP}$, results in deterministic switching of the free layer without over-rotation (360 degree rotation). By using spin torque asymmetry to realize an enhanced effective $P_{IPP}$, we experimentally demonstrate this behavior in OST devices. Modeling predicts that decreasing the effective demagnetization field can substantially reduce the minimum $C_{P}$ required to attain deterministic bipolar switching, while retaining low critical switching current, $I_{p\, }=$ 500 $\mu $A.