Dynamic vortex-antivortex interaction in a single cross-tie wall

A fascinating property of micromagnetism comes from the possibility to control the domain and vortex configuration through the sample shape and size. For instance, in a rectangular platelet a configuration containing a stable combination of two vortices and an antivortex can be created. Such a single cross-tie wall can be understood as being a coupled micromagnetic system with three static solitons. Here we report on its magnetization dynamics including the vortex-antivortex interactions [1]. The spectrum of eigenmodes is investigated as well as the effect of different vortex core orientations. These are important for the magnetization dynamics since they determine the sense of rotation for the gyrotropic motion. Since three cores are present in total 23 = 8 configurations are possible. On the left side of the figure micromagnetic simulations of the vortex (left, right) and antivortex displacements upon field pulse excitation are shown for the first 16 ns. It is clearly observed that different types of configurations lead to completely different dynamic behaviors. The origin is the dynamic coupling of the cores which is mediated by the exchange coupling through the adjacent domain walls. This coupling is significant and introduces unexpected effects, such as the quenching of gyrotropic motion for the antivortex in certain core configurations. Another consequence is the absence of simple eigen modes describing the vortex gyration. The experimental investigation of the vortex core dynamics by means of time-resolved photoemission electron microscopy using x-ray magnetic dichroism as a contrast mechanism allows to determine the actual core configuration although the lateral core size is below the spatial resolution of the microscope. This is done by comparing the experimentally determined core displacements with the micromagnetically simulated ones as shown on the right side of the figure.