Oscillatory transformative domain wall inner structure of the depinning domain wall around a notched ferromagnetic wire

We have investigated the domain wall (DW) depinning behavior around the symmetric notches in ferromagnetic nanowires by means of a micromagnetic simulation. We observed that the depinning field decreases as the size of the notch increases. The change in the ratio of the height to the length of the bottom of the triangular notch is also considered, and a relatively insensitive variation of the depinning field is observed with for ratios greater than 2. When the depinning field strength is varied, the DW internal structure is found to change during the depinning process. At a lower depinning field (< 4 mT), the DW keeps its initial transverse wall structure whereas at a higher depinning field (> 4 mT), the DW is depinned with a transformation of the inner structure with an antivortex soon after the DW has escaped from the notch due to the Walker breakdown phenomenon. Very interestingly, with any external field, the depinned DW with antivortex inner structure is observed to move back to the original notch position. This is explainable because the notch acts as an attractive pinning potential for the DW.