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Titolo:
CRITICAL-CURRENT, MAGNETIZATION RELAXATION AND ACTIVATION-ENERGIES FOR YBA2CU3O7 AND YBA2CU4O8 FILMS
Autore:
WEN HH; SCHNACK HG; GRIESSEN R; DAM B; RECTOR J;
Indirizzi:
FREE UNIV AMSTERDAM,FAC PHYS & ASTRON,DE BOELELAAN 1081 1081 HV AMSTERDAM NETHERLANDS FREE UNIV AMSTERDAM,FAC PHYS & ASTRON 1081 HV AMSTERDAM NETHERLANDS
Titolo Testata:
Physica. C, Superconductivity
fascicolo: 3-4, volume: 241, anno: 1995,
pagine: 353 - 374
SICI:
0921-4534(1995)241:3-4<353:CMRAAF>2.0.ZU;2-2
Fonte:
ISI
Lingua:
ENG
Soggetto:
HIGH-TC SUPERCONDUCTORS; HIGH-TEMPERATURE SUPERCONDUCTORS; UPPER CRITICAL-FIELD; FLUX-CREEP; II SUPERCONDUCTORS; Y2BA4CU8O16 FILMS; INVERSION SCHEME; CURRENT-DENSITY; THIN-FILMS; DEPENDENCE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
38
Recensione:
Indirizzi per estratti:
Citazione:
H.H. Wen et al., "CRITICAL-CURRENT, MAGNETIZATION RELAXATION AND ACTIVATION-ENERGIES FOR YBA2CU3O7 AND YBA2CU4O8 FILMS", Physica. C, Superconductivity, 241(3-4), 1995, pp. 353-374

Abstract

By means of high-sensitivity capacitance torque magnetometers we havemeasured the superconducting current j(s) and the dynamic magnetic-moment relaxation of YBa2Cu3O7 and YBa2Cu4O8 films of typically 100 nm thickness at temperatures between 2 K and T-c in magnetic fields up to 6 T. For the measurements of the dynamic relaxation rate Q = dlnj(s)/dln(dB(e)/dt) magnetic-field sweep rates were varied between 0.5 and 40mT/s. At low fields (typically 0.5 T) the dynamical relaxation rate exhibits a plateau at Q approximate to 0.06 in YBa2Cu3O7 and 0.04 in YBa2Cu4O8. At high fields (B-e = mu(0)H(e) approximate to 6 T) the plateaus have completely disappeared and Q increases almost linearly with increasing temperature. At all fields a sharp increase up to Q congruent to 1 is observed when the irreversibility line is approached. By means of the generalized inversion scheme (GIS), the j(s)(T, B-e) and and(T, B-e) data are used to determine the current dependent activation energy U(j, T, B-e) for thermally activated flux creep. Although the GIS does not make any a priori assumptions about the explicit functionaldependences on T and j, the U(j, T = O, B-e) function derived from the experimental data by means of the GIS can remarkably well be described with the collective-creep interpolation formula U(j) = (U-c/mu)[ (j(c)/j)(mu)-1] with mu approximate to 0.6 for currents j > 0.15j(c)(T =0, B-e) where j(c)(T = 0, B-e) is the critical current at T = 0, and with U-c depending on B-e. At lower current densities U(j, T = 0, B-e)does not diverge as j(-0.6) but shifts gradually to a weaker 1n(j(c)/j) dependence. At low temperatures the current and relaxation data cannot be explained in terms of a thermally activated flux-motion model. Quantum creep has an influence up to similar to 13 K.

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Documento generato il 18/01/20 alle ore 10:35:11