No abstract

Micron-sized ferromagnetic permalloy disks having an in-plane vortexlike configuration are excited by a fast-rise-time magnetic-field pulse perpendicular to the plane. The excited modes are imaged using timeresolved magneto-optic Kerr microscopy and Fourier transformation. Two types of modes are observed: modes with circular nodes and modes with diametric nodes. The frequency of the modes with circular nodes increases with the number of nodes. In contrast, the frequency of the modes with diametric nodes decreases with the number of nodes. This behavior is explained accurately by an analytical model.

Thin-circular lithographically defined magnetic elements with a spin vortex configuration are excited with a short perpendicular magnetic field pulse. We report the first images of excited magnetic eigenmodes up to third order, obtained by means of a phase sensitive Fourier transform imaging technique. Both axially symmetric and symmetry breaking azimuthal eigenmodes are observed. We observe strong oscillations of the magnetization in the central part of the magnetic elements. The experimental data are in good agreement with micromagnetic simulations.

Within the framework of the Landau-Lifshitz-Gilbert equation, using permalloy parameters, we study the statics and dynamics of flat circular magnetic nano-structures with an in-plane magnetic vortex configuration, putting particular emphasis on the vorticity of the magnetic state and on the (perpendicular) polarisation of the vortex center, which may be shifted with respect to the center of the circle. These binary degrees of freedom can in principle be used to manipulate two independent bits of information.Studying switching processes induced by in-plane and out-of plane field pulses we find that it is possible to switch the vorticity of the magnetic dot on a time scale of 40 ps in strong enough and short enough perpendicular external field pulses (B ext z ≈ 0.5 T, duration ≈ 40 ps). But for realistically small values of the Gilbert damping, only the vorticity can be switched this fast, and it turns out that it is better to dismiss the center of the circle totally, concentrating on flat 'nano-rings' with an inner radius R 1 and an outer radius R 2 . On these 'nano-rings' the vortex state is more stable, and with respect to the switching of the vorticity these structures have similar properties as circular dots.

No abstract