Magnetization jumps and critical currents in YBa2Cu3O7-δ single crystals

To study the effect of Y2BaCuO5 (211 phase) precipitates on the flux jumps which appear at very low temperatures in YBa2Cu3O7-δ single crystal magnetization curves, three crystals have been used, of which two contain the 211 phase, in different proportions; the third reference sample being devoid of these precipitates. Our results show for the first time that the regularity of flux jumps is intimately connected with flux pinning mechanisms. For a field H applied perpendicular to the c-axis, lowering the temperature down to 1.5 K, we have not observed any jump, indicating that these precipitates constitute a factor of stabilization for this system.