Flux properties in Bi-2212 single crystals studied by spin-probe ESR

Flux properties in Bi2Sr2CaCu2O8+x (Bi-2212) single crystals are studied by spin-probe method. ESR line widths of a very thin layer of DPPH free radic al on the surface of the crystals begin to increase upon the superconductin g transitions. At further low temperatures below irreversibility lines, dis tinct hysteresis is observed between ESR profiles for field increase and de crease. The resonance fields and intensities also indicate characteristic c hanges. Close correlations between ESR anomalies and vortex behaviors are d iscussed, comparing results of as-grown and optimally doped crystals. (C) 2 000 Elsevier Science B.V. All rights reserved.