Hysteresis losses and magnetic phenomena in ribbons of type II superconductors in the noncollinear regime

Abstract

We have measured hysteresis losses, W (ho, hb' H bO ) ' in ribbons ofVTi and Nb subjected to oscillating magnetic fields of various amplitudes ho directed transverse to a static bias magnetic field H bO ' hence the name, noncollinear regime. A second bias field hb along ho may also be introduced. HbO and ho are directed along the length and width of the ribbon respectively or vice versa (90· rotation). The families of data curves are compared with the predictions of double criticalstate models where (i) dB I dx = ± F p (B )1 B governs the critical gradients of the magnetic induction and (ii) dO Idx = ± Fp(B )F(O )/B 2, the spatial variation of the orientation of the sheets offlux lines, with 0 = OalongH bo . The effect on W(ho,hb ,H bO ) ofchoosingF(O ) = l/tan 0, k and k I( 1 + 10 1)2 is illustrated and the latter is seen to yield the best agreement. The locus of the magnetization along the length and width of the samples, (M II ) and (M 1 ), have been monitored separately and simultaneously during the cycles of ho(t) for various ho andH bo with hb = ° or h o . These observations, in particular the curves of the magnetization along H bO ' constitute severe tests of any model. The corresponding curves generated by the model using F (0) = k I( 1 + 10 1)2 are presented. The physical origin of F(O) is explored.

Flux-cutting and flux-transport effects in type-II superconductor slabs in a parallel rotating magnetic field

“…[23,24]. The elliptic model also describes the behavior of < M y > (H y ) and < M z > (H y ) in crossed fields H y and H z [19,25], which was observed in the experiments on a VTi ribbon with nonmagnetic initial state [14,26]. Here, the good agreement with the experiment was achieved by using a relatively large anisotropy parameter J c /J c⊥ = 6.…”

“…The discovery of the phenomenon known as quasisymmetrical collapse of magnetization [1], which is observed in superconductors subjected to crossed magnetic fields and well interpreted within the simple Bean's critical-state model [2,3], has been a turning point in the understanding of the magnetic behavior of hard (irreversible type-II) superconductors. Until then, the generalized double critical-state model (GD-CSM) [4,5,6,7,8], which is based on fundamental physical concepts such as flux transport and fluxline-cutting [9,10], was successfully employed to explain a variety of experiments where flux cutting occurs [11,12,13,14,15,16]. An important feature of the GDCSM is the assumption that flux cutting and flux depinning do not affect each other.…”

“…Until then, the generalized double critical-state model (GD-CSM) [4,5,6,7,8], which is based on fundamental physical concepts such as flux transport and fluxline-cutting [9,10], was successfully employed to explain a variety of experiments where flux cutting occurs [11,12,13,14,15,16]. An important feature of the GDCSM is the assumption that flux cutting and flux depinning do not affect each other.…”

Magnetic response of hard superconductors subjected to parallel rotating magnetic fields

“…In particular, the DCSM explains satisfactorily the hysteresis losses of hard superconductors, which undergo slow oscillations in a static magnetic field 6 or are subjected to a time varying magnetic field orthogonal to a static bias field. 7 The double critical-state model was improved by Clem and Pérez-González [8][9][10][11][12][13][14] by allowing the existence of metastable zones where the magnitude of one or both current densities, perpendicular (J Ќ ) and parallel (J ʈ ) to the magnetic induction B, are smaller than the corresponding critical value. Within the framework of the generalized double critical-state model ͑GDCSM͒ the electric fields, which result from time-varying B profiles, obey Faraday's law and continuity across boundaries; this is not generally satisfied by the original DCSM.…”

A Semi-Infinite Superconductor with Monotonous Tc Variation

“…The new parameter J ck ðBÞ determines the threshold for the onset of flux-line cutting in the vortex array [4]. The double criticalstate model explains several experimental results observed in classical hard superconductors [11][12][13][14]. The extension of this double critical-state model to include the surface barrier effects has been considered in [15][16][17][18][19][20].…”