We study ns scale spin-torque-induced switching in perpendicularly magnetizedtunnel junctions (pMTJ). Although the switching voltages match with themacrospin instability threshold, the electrical signatures of the reversalindicate the presence of domain walls in junctions of various sizes. In theantiparallel (AP) to parallel (P) switching, a nucleation phase is followed byan irreversible flow of a wall through the sample at an average velocity of 40m/s with back and forth oscillation movements indicating a Walker propagationregime. A model with a single-wall locally responding to the spin-torquereproduces the essential dynamical signatures of the reversal. The P to APtransition has a complex dynamics with dynamical back-hopping whose probabilityincreases with voltage. We attribute this back-hopping to the instability ofthe nominally fixed layers.
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