HIGH-TC SUPERCONDUCTING FILM IN A TRANSVERSE AC MAGNETIC-FIELD - LOSSES AND EFFECT OF LOWER CRITICAL-FIELD

AC losses as a function of the amplitude of the AC transverse magnetic field are measured on both poly- and monocrystalline YBa2Cu3O7-delta superconducting films. The data are consistent with the calculation ba sed on the Bean critical state model adapted to a thin film perpendicu lar to a magnetic field. An influence of the 'lower critical field' H( c1)' (which first penetrates the sample) is observed on the monocrysta lline films, the value of H(c1) being about 0.1 times the 'true' H(c1) as known for bulk crystals. The technique described provides a simple method of determining critical current density and penetration fields in high-T(c) films.