Head-to-head domain walls in magnetic nanostructures

A review of geometrically confined 180 degrees head-to-head domain walls is presented. The spin structures of head-to-head domain walls are systematically determined by direct imaging and magnetotransport, and quantitative domain wall type phase diagrams are obtained and compared with available theoretical predictions and micromagnetic simulations. Discrepancies to the experiment are explained by taking into account thermal excitations, and thermally-induced domain wall type transformations are observed. The coupling between domain walls via the stray field leads to changes in the wall spin structure and the stray field intensity from a wall is found to decrease as 1/r with distance. Using the measured stray field values, the energy barrier height distribution for the nucleation of a vortex core is obtained. The pinning behaviour of domain walls at geometrical variations is discussed in detail and direct quantitative measurements of the width and depth of attractive potential wells responsible for the pinning are given. Dynamic measurements of resonant wall oscillations yield the exact shape of the potential well. Finally the domain wall propagation due to field and current is briefly discussed.