This study examined a pair of permanent magnets rotating above a tape-shaped single grain YBa2Cu3O8 (YBCO) superconducting sample (SS) with and without an applied bias current. The root-mean-square voltages (Vrms) induced by the forced movements of the vortices inside the SS were measured. At SS temperatures higher than the critical temperature (Tc) , the induced Vrms was a constant, as expected from Faraday’s law. However, at a temperature in the superconducting transition region, the induced Vrms is a sensitive function of both the motion of the magnet and the bias current applied to the SS. At temperatures below the transition region, the induced Vrms
did not drop to zero immediately. Instead, it dropped only to a particular value and then decreased as the temperature decreased. The experimental results obtained at temperatures in the superconducting transition region can be understood by considering the superposition of the two induced voltages. One is induced according to Faraday’s law, and the other one is induced by the flux flow inside the SS, which is caused by the bias current. At temperatures below the transition region, an explanation of how the magnetic field of a moving magnet passes through the superconductor is provided, and is consistent qualitatively with the experimental results. In this explanation, some of the magnetic field is assumed first to fill in and then to be pulled out from all sides of the SS in accordance with Bean’s model as the moving magnet passes through the SS from above.
Physical Review B (Condensed Matter and Materials Physics) 72(17), 172510(4pages)