Abstract
We have measured the current-induced voltage noise for both the thick and thin films of amorphous with strong pinning, over a broad frequency range, to study the effects of both the current I and magnetic field B on the vortex dynamics. The results show that the vortex dynamics probed by strikingly depends on the static vortex states. Irrespective of the film thickness, noise is largest at while small vortex shot noise is observed at high B in the vortex-liquid phase. The origin of large noise at is due mainly to density fluctuations of the thermally excited and subsequently grown vortex loops and dissociated vortex-antivortex pairs for three dimensions (3D) and 2D, respectively, in the presence of an applied current. In the three-dimensional vortex-solid phase, the -like noise spectra resulting from a plastic-flow motion of vortices are observed at low I over the broad field region, which is attributed to high concentration of pinning centers. With increasing I in the nonlinear regime, both the amplitude and spectral exponent β of decrease and eventually approach the values in the vortex-liquid phase.
- Received 26 October 1998
DOI:https://doi.org/10.1103/PhysRevB.61.671
©2000 American Physical Society