Observation of dendritic flux instabilities in YNi2B2C thin films

Magneto-optical imaging and magnetization measurements performed on thin films of the borocarbide superconductor YNi2B2C reveal the occurrence of magnetic flux instabilities upon reducing the applied magnetic field towards the remanent state. In contrast to other low-T-c materials such as Nb and MgB2, where similar instabilities occur in both increasing and decreasing magnetic fields, dendritic flux patterns are observed in YNi2B2C for decreasing fields only. Also in the magnetization measurements, a distinct asymmetry is evident between increasing and decreasing fields. The effect does not depend on the sweep rate of the field, but is strongly dependent on the maximum field applied before reduction. The observation of spontaneous flux instabilities in this additional family of low-temperature superconductors suggests that the responsible mechanism is universal to this class of materials. (C) 2004 American Institute of Physics.