  The authors have measured the magnetic response of 33 individual cold
mesoscopic gold rings, one ring at a time. The response of some sufficiently
small rings has a component that is periodic in the flux through the ring and
is attributed to a persistent current. Its period is close to h/e, and its sign
and amplitude vary between rings. The amplitude distribution agrees well with
predictions for the typical h/e current in diffusive rings. The temperature
dependence of the amplitude, measured for four rings, is also consistent with
theory. These results disagree with previous measurements of three individual
metal rings that showed a much larger periodic response than expected. The use
of a scanning SQUID microscope enabled in situ measurements of the sensor
background. A paramagnetic linear susceptibility and a poorly understood
anomaly around zero field are attributed to defect spins.
