The spin dynamics in narrow ferromagnetic rings is studied in the frequency range from 45MHzto20GHz at room temperature. Our broadband spectrometer allows us to monitor the ferromagnetic resonance of characteristic spin configurations as a function of an external field μ0H. We observe hysteresis and irreversible jumps of the resonance frequencies which we attribute to onion-to-vortex and vortex-to-reversed-onion transitions.

Magnetization processes of microstructured NiFe rings are studied by the fringe-field-induced local Hall effect and numerical model calculations. The changes in reversible and irreversible magnetization of single rings are detected with very high resolution. We observe that the type of magnetic transition depends on the ratio between the inner and outer ring diameter. For narrow rings, sharp transitions from so-called “onion” to the “vortex” state are observed. In rings with smaller inner diameter, the transitions are more complex. The creation of local vortices and their spatial movement by applying an external magnetic field are detected.

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