Collapse of the magnetization by the application of crossed magnetic fields: observations in a commercial Bi:2223/Ag tape and comparison with numerical computations

We report on the effects of crossed magnetic fields on a commercial Bi:2223/Ag tape superconductor. The large magnetic moments which are generated in the specimen by the application or change of an external magnetic field (denoted H-z) directed perpendicularly to the plane of the tapes, hence along the c-axis of the crystallites, are considerably reduced in magnitude when subsequently a magnetic field (denoted H-y) directed along the plane of the tape, hence along the ab plane of the crystallites, is impressed and removed and made to undergo several half cycles of oscillations in the opposite direction. We find that a few cycles cause the magnetic moment to rapidly depart from the critical state major hysteresis envelope and reach asymptotically the reversible diamagnetic Meissner moment M-rev, which is aligned in the out-of-plane direction of the tape (c-axis). We observe that the application of crossed fields, first along the c-axis, then along the ab plane, effectively suppresses the bulk pinning magnetic moment, and quenches the associated persistent currents circulating in the ab plane. Our numerical computations, based on the finite element method and using an E-J power law to model the superconductor, can reproduce qualitatively the experimental data. In the numerical model, the current density flows perpendicularly to the plane within which the two components of the magnetic field vary. These investigations show that the observed decay in magnetization results from the complicated modification of current distribution due to the application of crossed magnetic fields within the sample cross section.