Figure 1.

(a) SEM image of a 100 nm wide NiFe nanowire with Au pads for electrical contacts, and MFM image (inset) showing a DW pinned on the 50 nm wide constriction. (b) The DW motion is detected using a resistance measurement, probing both the AMR and the MMR, and a constant field is applied to the sample. A DW is introduced in the constriction, where it gets pinned for a while. The pinning time is stochastic, varying from experiment to experiment. Here are shown two examples of measurements realized using the same experimental conditions, but leading to different pinning times t₁ and t₂. (c) AFM and MFM images of a 200 nm wide FePt/Pd/FePt nanowire. The MFM image shows a single DW pinned on a 80 nm wide constriction. (d) Variation of the GMR as a function of time, associated to the motion of the DW between the two contacts. Here again, the two different pinning times obtained by repeating the measurement illustrate the stochastic behaviour of DW depinning.