We report on magnetic measurements of fluxoid transitions in mesoscopic, superconducting aluminum rings. The transitions are induced by varying the flux enclosed by the ring until instabilities are reached. In a temperature range near Tc, only a single fluxoid enters or leaves at a time, leading to a final state above the ground state. Upon lowering the temperature, several fluxoids enter or leave at once, and the final state approaches the ground state, which can be reached below approximately 0.5 Tc.
We propose a model for the evolution during the transition process which, although oversimplified, reproduces successfully the qualitative behavior found in the experiment. An essential ingredient in the model is heating due to the decay of the initial metastable state. The model enables us to envision the detailed evolution of the system variables during the decay and isolate the influence of different model parameters, such as heat capacity, electromagnetic and order parameter time constants, and thermal fluctuations.