Magnetization Splitting And Vortex Dynamics In Magnetic Nano-Structures:Micromagnetic Simulation

Magnetic nanostructures is an active study aspect, not only for its high sensitivity function or excitations of magnetic moments for practical application, but also as good candidates in research on some fundamental and interesting magnetism physics. Their domain structures and magnetic properties are strongly related with a few intrinsic parameters, such as magnetization, exchange coefficient, and anisotropy constant. Moreover, the size, the aspect ratio, and the thickness of the magnetic nano-strusture have a dramatic impact on the magnetic properties, especially when the size is comparable to the exchange length.The distributions of magnetization orientation for both Landau and diamond domain structures in nano-rectangles have been investigated by micromagnetic simulation. Both symmetric and asymmetric magnetization splitting are found in diamond domain structure, as well as only symmetric magnetization splitting in Landau structure. The magnetization splitting can take place around both the easy axis and the hard one. These indicate that the magnetization splitting is a general behavior in both Landau and diamond domain structures. In the Landau structure, the splitting angle increases with the exchange coefficient but decreases slightly with the anisotropy constant, suggesting that the exchange interaction mainly contribute to the magnetization splitting in Landau structure. However in the diamond structure, the splitting angle increases with the anisotropy constant but decreases with the exchange coefficient, indicating that the magnetization splitting in diamond structure is mainly resulted from magnetic anisotropy. For both Landau and diamond domain structures, the magnetization splitting depends strongly on the size. In the case of the easy axis along the length direction, the magnetization splitting angle around the easy axis is enhanced with the length of the easy axis, while that around the hard axis increases with the length of the hard axis. These results can extend the understanding of the basic features of the magnetic domain microstructures.The coupling of double magnetic vortices in a nano-rectangle (diamond) structure has been studied by micromagnetic simulation. Dynamics of double vortices at the sub-GHz gyrotropic frequency is excited by applying an in-plane magnetic field of a few mT at a half of the rectangle. The translation mode eigenfrequency of the vortex increases with the exchange coefficient. The frequency of the vortex excitation can be either blue-shift or red-shift by the partially applied positive field. Remarkably, the frequency of the vortex excitation has a minimum at a critical applied field, which is related to the competition between the displacement of each vortex core equilibrium position relative to the original position and the separation of the two vortices core positions.