THE EPR STUDY OF THE MAGNETIC-FLUX DISTRIBUTION ON THE SURFACE OF A SUPERCONDUCTING YBA2CU3OY SINGLE-CRYSTAL

The study is performed of the 9.3 GHz EPR signal in the 0.06 mm diphenyl picrilhydrazil grain set in the center of a high - T(c) YBa2Cu3Oy single crystal lamina. Below the superconducting transition temperature T(c) = 92 K the shift and broadening of the paramagnetic resonance line are observed, the line width and position being depended on the cooling conditions and external magnetic field direction. The results obtained may be well described within the critical state model and the value J(c) = = 1.2.10(6) A/cm2 at T = 4.2 K is found. The high sensitivity of the measurement procedure to the magnetic flux inhomogeneity allows to reveal the presence of the strong inhomogeneity in the critical current density distribution in single crystals.