Figure 4. Cumulative probability functions P(t) of depinning at constant magnetic fields, for various DC currents.

These curves show the bipolar effect due to the spin transfer torque on the depinning probability. In both FePt and NiFe systems the current-field equivalence can be generalized for the three kind of depinning processes, (a, f): simple path, (b, g): serial paths, (c, h): alternative paths. Figs. (d, e) and (i, k) shows the characteristic pinning time in the case of the simple path behavior, as a function of the applied field (d) and the applied currents (e) for FePt and (i,k) NiFe. The symbols represent experimental results and the solid lines illustrate a linear fit on a log scale.