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AC Measurements on Hard Superconductors
Author(s) -
Ullmaier H. A.
Publication year - 1966
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.19660170220
Subject(s) - condensed matter physics , pinning force , superconductivity , magnetic field , vortex , current density , critical field , critical current , voltage , current (fluid) , flux pinning , type ii superconductor , materials science , field (mathematics) , physics , mechanics , thermodynamics , mathematics , quantum mechanics , pure mathematics
Cylindrical samples of PbIn, NbZr, and NbTa were exposed to a longitudinal, static magnetic field with a collinear alternating field, and the voltages produced in pick up coils wound around the samples were observed on an oscilloscope. The shape of the voltage‐time curves can be adequately explained by considering a surface sheath which is able to carry a certain critical surface current and a bulk region where the pinning forces dominate the magnetic behavior. It is shown that an analysis of the voltage‐time curves obtained yields values for the critical surface current and the bulk critical current density which are in good agreement with static measurements. While the bulk critical current density goes to zero when the external field reaches the upper critical field H c2 , the surface currents can be seen up to a field H c3 > H c2 . Values of the bulk critical current density obtained were then used to determine the pinning force per unit volume and the pinning force on a single vortex line, as a function of the vortex line density.