  Current-induced spin-transfer torques (STT) and spin-orbit torques (SOT)
enable the electrical switching of magnetic tunnel junctions (MTJs) in
nonvolatile magnetic random access memories. In order to develop faster memory
devices, an improvement of the timescales underlying the current driven
magnetization dynamics is required. Here we report all-electrical time-resolved
measurements of magnetization reversal driven by SOT in a three-terminal MTJ
device. Single-shot measurements of the MTJ resistance during current injection
reveal that SOT switching involves a stochastic two-step process consisting of
a domain nucleation time and propagation time, which have different genesis,
timescales, and statistical distributions compared to STT switching. We further
show that the combination of SOT, STT, and voltage control of magnetic
anisotropy (VCMA) leads to reproducible sub-ns switching with a spread of the
cumulative switching time smaller than 0.2 ns. Our measurements unravel the
combined impact of SOT, STT, and VCMA in determining the switching speed and
efficiency of MTJ devices.
