Abstract
Vortex avalanche phenomenon enhanced by thermomagnetic instabilities suppresses critical current in MgB2 films. This effect is investigated at 4.2K by spectral noise power measurements up to 1kHz with a dc superconducting quantum interference device apparatus. 1∕fγ behavior is shown at low frequencies in magnetic fields and feeding currents below jc. γ increases from 1 to 2 at increasing magnetic field, typical of fluxon avalanche processes. A peak in the power spectrum frequency behavior, observed only in magnetic field, is attributed to vortex–antivortex annihilations. Thermal instabilities disappear when an efficient thermal link to the He bath is attained and no vortex avalanche extra-noise is observed.
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