  Ta/CoFeB/MgO trilayers with perpendicular magnetic anisotropy are expected to
play a key role in the next generation of current and electric field switched
memory and logic devices. In this study we use Kerr microscopy alongside
electrical transport measurement to gain insight into the underlying switching
mechanisms of such devices. We find switching to be a stochastic, domain wall
driven process, the speed of which is strongly dependent on the switching
current. Kerr imaging shows domain nucleation at the edge of the device which
modelling reveals is likely assisted by the perpendicular component of the
Oersted field. Further domain growth, leading to magnetisation reversal may be
assisted by spin torques.
