Flux dynamics and vortex phase diagram of the new superconductor MgB2

Citation
Hh. Wen et al., Flux dynamics and vortex phase diagram of the new superconductor MgB2, PHYSICA C, 363(3), 2001, pp. 170-178
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
PHYSICA C
ISSN journal
0921-4534 → ACNP
Volume
363
Issue
3
Year of publication
2001
Pages
170 - 178
Database
ISI
SICI code
0921-4534(20011115)363:3<170:FDAVPD>2.0.ZU;2-O
Abstract
Magnetic relaxation, critical current density and transport properties have been investigated on MgB2 bulks from 1.6 K to T-c at magnetic fields up to 8 T. A vortex phase diagram is depicted based on these measurements. Two p hase boundaries H-irr(bulk) (T) and H-irr(g)(T) characterizing different ir reversible flux motions are found. The H-irr(bulk)(T) is characterized by t he appearance of the linear resistivity. A large separation between the bul k irreversibility field at 0 K and the upper critical field H-c2(0) has bee n found, it is interpreted as either due to a quantum vortex liquid induced by strong quantum fluctuation of vortices at 0 K, or flux flow through wea k-link channels. It is further found that the magnetic relaxation rate is w eakly dependent on temperature but strongly dependent on field indicating a trivial influence of thermal fluctuation on the vortex depinning process. Therefore the phase line H-irr(bulk) (T) may be attributed to quantum vorte x melting in the rather clean system at a finite temperature. The second bo undary H-irr(g)(T) reflects the irreversible flux motion in some local regi ons due to either very strong pinning or the surface barrier on the tiny gr ains. (C) 2001 Elsevier Science B.V. All rights reserved.