Domain wall based nanosecond-scale switching process in perpendicularly magnetized STT-MRAM cells

We study the duration of the switching events in perpendicular magnetized spin-transfer-torque magnetic random access memory cells. We focus on the sub-threshold thermally activated switching in optimal applied field conditions. From the electrical signatures of the switching, we infer that once the nucleation has occurred, the reversal proceeds by a domain wall sweeping though the device at a few 10 m/s. The smaller the device, the faster its switching. We present an analytical model to account for our findings. The domain wall velocity is predicted to scale linearly with the current for devices much larger than the wall width. The wall velocity depends on the material parameters, such that the best performing devices in term of low switching current density will be the ones that host the domain walls with the lowest mobilities.