An anisotropic model for describing the critical state of hard superconductors subjected to crossed and rotating magnetic fields is proposed.

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The magnetic response of anisotropic irreversible type-II superconductors is investigated theoretically. Using an elliptic vertical law for the electric field E as a function of the current density J, we have reproduced available experimental magnetization curves of YBCO samples with the c axis lying in the sample plane. Specifically, we could reproduce quantitatively and interpret correctly the appearance of additional extrema and segments with relatively small slopes of the virgin magnetization curves when the direction of the applied magnetic field differs from the principal axes. The notable deformation of magnetization curves in a tilted magnetic field is connected to the strong coupling between the components of the magnetic induction.

Articles you may be interested inAnalysis of magnetic response of critical state in second-generation high temperature superconductor YBa 2 Cu 3 O x wire

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The study of electric field distributions induced by flux creep in type-II superconducting films allows for important insight into the mechanism of vortex dynamics, the temporal evolution of flux and current distributions, and the occurrence of local losses. Most studies are based on the assumption that a phenomenological materials law, which has been extracted from macroscopic transport measurements, can be also applied to the local electric field during magnetization decay. We evaluate this ansatz by reconstructing the threedimensional-induced E i and potential E p electric fields from experimentally measured time dependence of the flux density distribution. The results are quantitatively compared with solutions of the nonlinear and nonlocal equation of motion for the flux penetration, where the Maxwell equations as well as a materials law are utilized to obtain a two-dimensional E i,2D and E p,2D . We focus our analysis on the electric field distributions on a partially penetrated magnetized state of an epitaxial YBa 2 Cu 3 O 6.95 film.

Experimental results of a type-II superconductor, undergoing slow oscillations in a static magnetic field, have been theoretically investigated. The theoretical description considers the occurrence of flux-line cutting since the critical currents have a parallel component to the magnetic induction B. For this purpose, the elliptic flux-line-cutting critical-state model has been employed to calculate the magnitude B and orientation α(x) of the magnetic induction. Hysteresis loops, at different initial magnetic states and, at relatively small and large amplitudes of oscillation, are calculated numerically and compared with experimental data of a Nb disk. The complex behavior of the hysteresis loops is associated with the magnetic induction consumption. Our results are compared with those obtained employing the generalized double critical-state model. Our elliptic model is not restricted by the isotropic condition, that establishes that the electric field E is parallel to the current density J, but considers an induced anisotropy by flux line cutting. The limits of applicability of the elliptic model are discussed.