DIAMAGNETIC PROPERTIES OF RBXC60 FINE POWDERS

The temperature and field dependence of AC - susceptibility chi has be en measured for two RbXC60 fine powders. For x=3, chi(T) obtained in a DC magnetic field H approximate to 1kOe, corresponds to the Meissner state of separate grains, which size is less than the London penetrati on depth lambda. Experimentally obtained lambda(T) perfectly accounts for BCS dependence in dirty limit. In the case of x greater than or eq ual to 3 (a little excess of Rb) the fast quenching from 250 degrees C raises the shielding 10 times, while a room temperature annealing dec reases chi, which finally reaches the same value as in the case of x=3 . This reversible change of chi is ascribed to the intergrain screenin g currents.