6 Experimental Results 6.3 Investigation of the lifetime of quantized spin waves in nano-scaled mag- netic ring structures

The investigation of the magnetic excitation spectrum of magnetic nano-structures is of large im-portance for the fundamental understanding of the magnetization dynamics as well as for techno-logical applications. The demands concerning speed and reliability for future logic and data storage devices are pushing the operating frequency towards the GHz-regime – the typical time-scale of spin waves, the fundamental excitations of the magnetization. Since the discovery of the spin-wave quantization effect in patterned magnetic thin films [1, 2] many works focused on the research of eigen-excitations in magnetic media with a reduced dimensionality. The amplitude profile, the discrete frequencies and the quantization conditions of spin-wave eigenmodes in stripes [1–4], rectangles [4,5], disks and ellipses [6,7] are now well understood and allow nowadays even for an engineering of the spin-wave eigenmode spectrum in such a small magnetic structure taking into account issues of geometric shape, multilayer stacks, and even magnetic domain structure. The magnetization dynamics of rings magnetized in the onion state show a large richness of possi-ble eigenmodes. Quantization of spin waves takes place not only due to the confinement in radial and azimuthal direction in the so-called equatorial regions at 90 ◦ and 270 ◦ (see inset in Fig. 1 for the definition of the angular positions) but also in spin-wave wells in the so-called pole regions a