Observation of coherence and partial decoherence of quantized spin waves in nanoscaled magnetic ring structures.

Experiments and simulations are reported, which demonstrate the influence of partial decoherence of spin-wave modes on the dynamics in small magnetic structures. Microfocus Brillouin light scattering spectroscopy was performed on 15 nm thick Ni81Fe19 rings with diameters from 1 to 3 microm. For the so-called "onion" magnetization state several effects were identified. First, in the pole regions of the rings spin-wave wells are created due to the inhomogeneous internal field leading to spin-wave confinement. Second, in the regions in between, modes are observed which show a well pronounced quantization in radial direction but a transition from partial to full coherency in azimuthal direction as a function of decreasing ring size. In particular for larger rings a continuous frequency variation with position is observed which is well reproduced by spin-wave calculations and micromagnetic simulations.