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Titolo: CRITICALCURRENT, MAGNETIZATION RELAXATION AND ACTIVATIONENERGIES 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: 34,
volume: 241,
anno: 1995,
pagine: 353  374
 SICI:
 09214534(1995)241:34<353:CMRAAF>2.0.ZU;22
 Fonte:
 ISI
 Lingua:
 ENG
 Soggetto:
 HIGHTC SUPERCONDUCTORS; HIGHTEMPERATURE SUPERCONDUCTORS; UPPER CRITICALFIELD; FLUXCREEP; II SUPERCONDUCTORS; Y2BA4CU8O16 FILMS; INVERSION SCHEME; CURRENTDENSITY; THINFILMS; DEPENDENCE;
 Tipo documento:
 Article
 Natura:
 Periodico
 Settore Disciplinare:
 Science Citation Index Expanded
 Citazioni:
 38
 Recensione:
 Indirizzi per estratti:



 Citazione:
 H.H. Wen et al., "CRITICALCURRENT, MAGNETIZATION RELAXATION AND ACTIVATIONENERGIES FOR YBA2CU3O7 AND YBA2CU4O8 FILMS", Physica. C, Superconductivity, 241(34), 1995, pp. 353374
Abstract
By means of highsensitivity capacitance torque magnetometers we havemeasured the superconducting current j(s) and the dynamic magneticmoment relaxation of YBa2Cu3O7 and YBa2Cu4O8 films of typically 100 nm thickness at temperatures between 2 K and Tc in magnetic fields up to 6 T. For the measurements of the dynamic relaxation rate Q = dlnj(s)/dln(dB(e)/dt) magneticfield 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 (Be = 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, Be) and and(T, Be) data are used to determine the current dependent activation energy U(j, T, Be) 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, Be) function derived from the experimental data by means of the GIS can remarkably well be described with the collectivecreep interpolation formula U(j) = (Uc/mu)[ (j(c)/j)(mu)1] with mu approximate to 0.6 for currents j > 0.15j(c)(T =0, Be) where j(c)(T = 0, Be) is the critical current at T = 0, and with Uc depending on Be. At lower current densities U(j, T = 0, Be)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 fluxmotion 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