A NEW LOWER CRITICAL FIELD AND ANOMALY OF MAGNETIZATION CURVE IN HIGH TcY1Ba2Cu3O7−δ BULK SUPERCONDUCTORS

Abstract

The magnetization behaviors of single phase Y1Ba2Cu3O7−δ bulk superconductors have been studied by measurement of the DC susceptibility. It is found that there are two lower critical field. One which is near 10 Oe at 77K is defined as a weak lower critical field and denoted by HclJ. dHc1J/dT is about 0.2 Oe/K near Tc. Another is still called as usual lower critical field, Hcl. It is 60 Oe at 77K and dHc1/dT is about 4.6 Oe/K. The detailed measurement of DC magnetization shows also that an anomaly of the magnetization curve appears between HclJ and Hc1. The amplitudes of anomalous peak and valley have some difference depending on how samples are prepared. The mechanism of Hc1J appearance and the anomaly of the magnetization has been discussed in “Soft Sponge Model” which will be published in Chin. J. Low Temperature Physics.