Evidence for individual vortex pinning in ceramic YBa2Cu3O7−δ

Abstract
We measured the pinning force density Fp in high quality YBa2Cu3 O7−δ ceramics as a function of the temperature and magnetic field up to 5 T. The results indicate that near 60 K the magnetic vortices are pinned individually. This implies that at this temperature the main pinning mechanism involves localized pinning centers separated by short distances rather than twin boundaries.