Micromagnetic simulation of 360° domain walls in thin Co films

A moving mesh finite element technique is applied to simulate the formation and annihilation of 360 degrees wall structures in thin Co films. Adaptive refinement and coarsening of the finite element mesh controls the discretization error during the simulation of domain wall movement. Elements are refined in regions with high variation of the magnetization, whereas elements are taken out where the magnetization is uniform. The calculated Neel walls have very wide tails and have an extension of about 15-20 nm. The motion of domain walls through the sample gives rise to the formation of 360 degrees domain walls. They are formed when a Bloch line in a domain wall is caught at a nonmagnetic defect in the sample. Pinholes with an extension greater than 6 nm are sufficient to trap a Bloch line. The width of the 360 degrees walls is found to be in the range of 40 to 50 nm. The stability of the 360 degrees walls depends on the strength of the pinning of the Bloch lines. The field required to annihilate the 360 degrees walls increases linearly with the size of the nonmagnetic defect. (C) 2000 American Institute of Physics. [S0021-8979(00)81608-4].