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.

We study the dynamics of flat circular permalloy nanomagnets for 1.) magnetic vortex and 2.) single-domain configurations using micromagnetic simulation. Dynamical studies for isolated vortex structures show that both the vorticity and the polarity of the out-of-plane component can be switched fast (50-100 ps). Micromagnetic simulations of the switching process in thin cylindrical Permalloy(Py) nanoparticles with an initial stable singledomain state show nearly homogeneous single-domain behavior followed by excitation of spin waves. The magnetism of small ferromagnetic structures has become increasingly important e.g. for nonvolatile random access memories (MRAMs) [1]. Nanostructured Permalloy is a possible candidate for such devices. As it is an essential feature in the technology of magnetic recording to read and write magnetic states as fast as possible we study the dynamics of flat circular permalloy nanomagnets with magnetic vortex or singledomain configuration using micromagnetic simulations.There are four equivalent vortex states since the vorticity (clockwise/counterclockwise) and the central polarization (up or down) are independent. The possibility of storing and switching two bits of information instead of only one makes these vortex structures quite interesting.It is known from [3] that the vorticity of a magnetic dot can be switched in ≈ 40 ps with strong enough and short enough perpendicular out-ofplane field pulses.In the present work, we consider 1.) the question, whether also the polarization can be switched reproducibly and as fast as the vorticity.Therefore the results of a micromagnetic simulation performed with OOMMF, [4], on a cylindrical Py dot with diameter 300 nm and 10 nm thickness are shown. We have used Py param- * Tel.: +49-941/9432605; Fax: +49-941/9434544; E-mail address: andreas.killinger@physik.uni-regensburg.de eters (M s = 800000 A m for the saturation magnetisation, A = 1.3 * 10 −11 J m for the exchange stiffness and α = 0.008 for the Gilbert damping). The initial magnetisation configuration is a (relaxed) vortex state. We apply a typical out-ofplane field pulse (100 ps duration) of B z = 0.2 T, plus B x = 0.002 T to induce torque at x = y ≈ 0.