Hysteresis in the flux flow characteristics of a type II superconductor associated with the presence of normal metal precipitates

Unusual history-dependent flux flow properties are observed in a Pb_0.871Sn_0.129 alloy as tin precipitates from solution at room temperature. We find that the critical currents and flux flow curves depend upon the field history, the current history, and the orientational history of the sample. Two volume pinning force curves are observed with different force magnitudes and field locations of the force peak, depending upon whether the field is cycled to high fields or zero field before the force is measured. Flux flow noise measurements in these samples yield very low noise, consistent with our recent model, which predicts low noise in samples with closely spaced pinning centers that interrupt the flux motion. The experimental results are explained in terms of the formation of a nonequilibrium flux line lattice in the presence of precipitates, and the response of such a lattice to current, field, and orientational changes.Research Supported by U.S. ERDA Grant No. EY-76-S-02-2890. Items of equipment used in this work were provided by a Research Corporation Grant.