For the first time the influence of irradiation-induced columnar defects (0.5 GeV I-ions) on flux line pinning in Bi-2212 crystals has been investigated by means of the high-resolution magneto-optical Faraday effect. By irradiating only a part of each sample, the local change in the flux pinning has been determined. Irradiated and nonirradiated parts have been investigated simultaneously under the same experimental conditions. At T = 5 K and μ0Hext = (0 4 300) mT a large enhancement of jc m is found in the irradiated region. The observation of the time dependence of the flux density distribution yields small values for the pinning potential U, supporting the model of two-dimensional pancake vortex pinning.
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