Early stages of magnetization relaxation in superconductors

TitleEarly stages of magnetization relaxation in superconductors
Publication TypeJournal Article
Year of Publication2013
AuthorsVanevic M, Radovic Z, Kogan VG
Journal TitlePhysical Review B
Date Published04
Type of ArticleArticle
ISBN Number1098-0121
Accession NumberWOS:000316994500002
Keywordscollective flux-creep, high-temperature superconductors, MOTION, vortices

Magnetic flux dynamics in type-II superconductors is studied within the model of a viscous nonlinear diffusion of vortices for various sample geometries. We find that time dependence of magnetic moment relaxation after the field is switched off can be accurately approximated by m(t) proportional to 1 - root t/(tau) over tilde in the narrow initial time interval and by m(t) proportional to (1 + t/tau)(-1) at later times before the flux creep sets in. The characteristic times (tau) over tilde and tau are proportional to the viscous drag coefficient.. Quantitative agreement with available experimental data is obtained for both conventional and high-temperature superconductors with eta exceeding by many orders of magnitude the Bardeen-Stephen coefficient for free vortices. Huge enhancement of the drag, as well as its exponential temperature dependence, indicates a strong influence of pinning centers on the flux diffusion. Notwithstanding the complexity of the vortex motion in the presence of pinning and thermal agitation, we argue that the initial relaxation of magnetization can still be considered as a viscous flux flow with an effective drag coefficient. DOI:10.1103/PhysRevB.87.144501

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