Magnetic imaging of the paramagnetic Meissner effect in the granular high-T_c superconductor Bi₂Sr₂CaCu₂O_x

Abstract

We have imaged the spatial distribution of magnetic flux on a granular sample of the high-temperature superconductor Bi2Sr2CaCu2Ox using a scanning SQUID microscope. Our results establish the presence of spontaneous orbital magnetic moments which were suggested to be the origin of the paramagnetic response of these materials. The signature of the orbital magnetic moments is a rather broad distribution of local magnetic fields at the surface of the sample. A simple model for the distribution is presented.