Time-resolved observation of domain-wall driven beyond the Walker field by vertical spin currents

We present time-resolved, non-averaged measurements of the displacement of magnetic domain-walls (DWs) driven by vertical spin-polarized currents in track-shaped magnetic tunnel junctions. In these structures we observe very high DW velocities (600 m/s) at relatively small current densities (< 10^7 A/cm^2), those velocities being greater than both the typically observed velocities with in-plane injected currents and the predicted velocities in the Walker breakdown DW propagation regime. We show that the efficient spin-transfer torque combined with a short propagation distance can effectively avoid the Walker breakdown process, and achieve deterministic, reversible and fast (~ 1 ns) DW-mediated magnetic switching.