Field driven domain wall dynamics in ferromagnetic nanostripes

I report on the dynamics of magnetic domain walls (DW) in ferromagnetic nanostripes. The investigations were carried out using the giant magnetoresistance effect, while the DW moved in a soft magnetic NiFe layer. This technique enabled me to verify for the first time the so called Walker Breakdown process in single shot measurements. Additionally I investigated the influence of an in plane transverse field (perpendicular to the movement direction of the DW) on the DW dynamics. It turned out that the DW mobility can be significantly increased, because of a change of the DW shape due to the effect of the transverse field. In the course of the single shot experiments I discovered a new kind of DW motion. Under the influence of a transverse field or in comparably wide nanostripes the DW is stretched along its movement direction. This longitudinal elongated DW is only dynamically stable and is a result of the interplay between the exchange energy and the demagnetization energy. The influence of the nanostripe real shape, in particular the shape of the cross section, on the DW behavior was investigated in another part of this thesis. It turned out that one finds different so called critical Walker fields in the same sample. This critical field depends theoretically on geometric and material parameters and thus should be the same for one sample. I could explain these findings with different stray field contribution in the region of the DW in dependence on the magnetization configuration inside the wall. In a last part I investigated the influence of a transverse field on the DW pinning process. Due to geometric imperfections of the nanostripe, e.g. edge roughness, the DW can be pinned to such a defect. I showed that a transverse field decreases the pinning probability of weak pinning sides. However, for strong pinning sites the probability can show complicated dependencies on the DW pinning process.


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