SURFACE-BARRIER AND MAGNETIC HYSTERESIS OF AC PERMEABILITY IN YBACUO SINGLE-CRYSTAL

The nature of hysteretic behavior of the flux line lattice (FLL) contr ibution to ac magnetic permeability (mu(v)) is analyzed for the case o f YBa2Cu3Ox single crystal (at applied magnetic field H perpendicular to c axis). It is shown that hysteresis loops mu(v)(H) corresponding t o different temperatures (T = 70-84 K) are scaled to a universal curve in normalized coordinates. Such a behavior is interpreted in terms of the FLL interaction with the crystal surface. The explicit relationsh ip between mu(v) and magnetic induction B is found for the near-surfac e region of the superconductor. It is shown that the mu(v)(H) loops ar e closely related to the hysteresis of B at cycling of applied magneti c field. The latter hysteresis stems from the Bean-Livingston surface barrier. The estimates demonstrate strong suppression of the surface b arrier in YBa2Cu3Ox crystal in comparison to that expected for the ide al surface. As a result, the lower branch of the hysteresis loop corre sponding to the increasing field is very close to the equilibrium mu(v )(H) curve and the surface barrier appreciably affects only the upper branch when magnetic flux leaves the sample. The comparison of theoret ical predictions and experimental data provides an opportunity to refi ne the actual range of stability H-max(B)-H-min(B) for the FLL at fixe d B for YBa2Cu3Ox crystal in the case of H perpendicular to c. (C) 199 8 Elsevier Science B.V. All rights reserved.