Effect of antidot on magnetization dynamics of permalloy nanowire

A systematic investigation of the magnetization dynamics of a rectangular shaped permalloy nanowire with an antidot is carried out using the micromagnetic simulations. The dynamic response of the nanowire without antidot exhibited two resonance modes corresponding to the bulk and edge modes. When an antidot was introduced within the nanowire, three prominent resonance modes are observed, namely, the branch mode, bulk mode, and the edge mode. The branch mode appeared at relatively higher frequency due to the spin excitations in the branches, bulk mode originated due to excitations in the region between antidot and edges of the nanowire, and the edge mode occurred due to localized inhomogeneity at the edges. When the antidot width is varied by maintaining a constant magnetic field, the frequency spectrum for bulk mode remains unchanged, whereas, we observed a shift in the resonance frequency of the branch mode. In contrast, when the length of the antidot is varied, there is a decrease in frequency observed in both branch mode and bulk mode. When the magnetic field is varied at constant antidot dimensions, the resonance frequency of the branch mode as well as the bulk mode increased. We observed that the changes in the resonance frequencies of different modes are majorly governed by the competing spin interactions influenced by the shape anisotropy and demagnetising fields during the excitation of the resonance modes. Additionally, these modes are also quite sensitive to the dimensions of the antidot. We show that by carefully adjusting the antidot geometry, the dynamic behaviour of these ferromagnetic nanowires could be tailored which is suitable for the microwave devices, magnetic sensors, and tunable magnonic filters.