Effects of 3.1-Mev Proton and 1-Gev Au-Ion Irradiation on the Magnetic Flux Noise and Critical Current

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We have used a dc superconducting quantum interference device to measure the spectral density of magnetic flux noise, (Formula presented), generated by vortex motion in crystals of (Formula presented) (YBCO) both before and after irradiation with 3.1-MeV protons and 1-GeV Au ions. In addition, we have studied the effects of irradiation on the critical current (Formula presented) of the same samples. Both types of irradiation reduced (Formula presented) at most temperatures and magnetic fields and increased (Formula presented) at all temperatures and magnetic fields. By measuring (Formula presented) versus temperature, we extract the distribution of vortex pinning energies, (Formula presented). Both crystals have peaks in (Formula presented) near 0.1 eV and 0.2 eV before irradiation, and a much reduced peak near 0.1 eV after irradiation. The noise level after either kind of irradiation was substantially higher than in an unirradiated YBCO film.



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