DETERMINATION OF THE QUENCHING TEMPERATURE FOR THE VORTEX LATTICE IN FIELD-COOLING DECORATION EXPERIMENTS

Field-cooled vortex patterns obtained with magnetic decoration, repres ent an equilibrium configuration of the vortices established in the sa mple at some temperature T-q, usually well above the actual temperatur e of decoration. This ''quenching'' temperature corresponds to the ons et of pinning in the sample and its knowledge is crucial for the inter pretation of the decoration data. We developed an experimental method to determine T-q and apply it to the conventional superconductor NbSe2 and the high-T-c, superconductor Bi2Sr2CaCu2O8-delta. In the latter c ase a variation of T-q of the order of a few Kelvin within the sample has been observed.