History dependence of the magnetization of thin HTSC films: an explanation for distorted SQUID signals

Abstract The magnetizations of thin film disk-shaped type-II superconductors in perpendicular magnetic fields are considered by aid of Mikheenko's critical state model which has been corrected by Zhu for the case of a time-varying periodic field. This paper presents the application of this scheme to an arbitrary nonperiodic time dependence H ( t ). We calculate the influence of field inhomogeneities in a magnetometer on the current density distribution of a disk-shaped type-II superconductor. The resulting SQUID pickup signals and magnetic moments are compared to measurements performed on a 200 nm thick YBa 2 Cu 3 O 7 film in the irreversible regime of the phase diagram. Theory and experime…