Abstract
After the discovery of high Tc superconductor, it was found in some specimens that they exhibited positive magnetic susceptibility in field-cooled regime when the applied field is small. This phenomenon is called paramagnetic Meissner effect now. There are several related theories, such as it-junction, and field compression. Because this phenomenon was also found in Nb disk, the theory of it-junction associated with d-wave superconductivity might be doubtful. In this study, we have done a series of magnetic measurement of several samples including high Tc films, Nb films and a YB@Cuft-, single crystal. In the measurement, we get both the zero-field-cooled and the field-cooled curves of magnetization with respect to temperature. We extract the field-cooled magnetization at T=5K and get the curve of field-cooled magnetization at T=5K with respect to the applied field. We find that the zero-field-cooled susceptibility is positive near Tc. Since there is no field to compress during the cooling, the the ry of field compression might also be doubtful. We suggest that another explanation might be needed. In addition, the linearity with positive slope of the saturated FC magnetization with respect to fields at high fields is first found in this study. For films, this linearity and positive field-cooled susceptibility are found at both low and high fields. For single crystal, they are found only when the applied field is sufficiently high.