  We have observed spontaneous magnetic moments with random signs in c-axis
oriented thin films of the high-Tc cuprate superconductor YBCO, imaged with a
scanning SQUID microscope. These moments arise when the samples become
superconducting, and appear to be associated with non-ferromagnetic defects in
the films. In contrast with granular high-Tc samples, which also show
spontaneous magnetization with random signs, these samples shield
diamagnetically.
