Magnetization and flux creep in thin YBa2Cu3O7−δ films of various thickness

Sheriff, E.; Prozorov, Ruslan; Yeshurun, Y.; Shaulov, A.; Koren, G.; Chabaud-Villard, C.

doi:10.1063/1.366169

Cited by 18 publications

(17 citation statements)

References 21 publications

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“…This dependence is very similar to that measured by Jooss et al 13 Other authors also report the increase of j as function of film thickness d, but with a maximum at dϷ100 nm followed by a much more rapid drop of j. 15,36,37 Proposed explanations 15,13 have been the increase of the effective penetration depth from ab towards 2 ab 2 /d for films thinner than 2 ab , 38 a bad film morphology and illconnected islands for dϽ100 nm, 36 and differences in defect structure between the thinner and the thicker films. 37 We note that the fact that films from different sources display maximum j for widely different film thicknesses, 100 nm and 250 nm, respectively, exclude that the relative magnitude of d and ab is at the origin of the increase of j(d).…”

Section: Discussionsupporting

confidence: 80%

Strong pinning in high-temperature superconducting films

et al. 2002

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Detailed measurements of the critical current density j c of YBa 2 Cu 3 O 7Ϫ␦ films grown by pulsed laser deposition reveal the increase of j c as a function of film thickness. Both this thickness dependence and the field dependence of the critical current are consistently described using a generalization of the theory of strong pinning of Ovchinnikov and Ivlev ͓Phys. Rev. B 43, 8024 ͑1991͔͒. From the model, we deduce values of the defect density (10 21 m Ϫ3 ) and the elementary pinning force, which are in good agreement with the generally accepted values for Y 2 O 3 inclusions. In the absence of clear evidence that the critical current is determined by linear defects or modulations of the film thickness, our model provides an alternative explanation for the rather universal field dependence of the critical current density found in YBa 2 Cu 3 O 7Ϫ␦ films deposited by different methods.

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Section: Discussionsupporting

confidence: 80%

Strong pinning in high-temperature superconducting films

et al. 2002

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“…7͒ observed at T ഛ 77 K by other groups. This thickness effect seems to be inherently determined by the lower activation energy associated with thinner films, which is confirmed by the observation of considerable increase of relaxation rate dM / dt in the thinner YBCO films at T ജ 70 K. 29 Although a quantitative comparison requires more detailed experimental studies, this experimental observation of J c -t curves agrees well qualitatively with the theoretical simulation of J c -t curves by considering the TAFM effect on the original CP model. 30 If the deviation of J c -t from the J c ϰ t −1/2 curve is caused mainly by TAFM, much enhanced effect is anticipated in the applied H since it reduces pinning potential and facilitates TAFM.…”

supporting

confidence: 77%

Effect of temperature and magnetic field on the thickness dependence of the critical current density ofYBa2Cu3O7−x
Wang
¹
,
Wu
²

2007
Phys. Rev. B
23
1
4
0
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In order to shed light on the puzzling thickness ͑t͒ dependence of the critical current density ͑J c ͒ in YBa 2 Cu 3 O 7−x ͑YBCO͒ films at 77 K and self-field, we have investigated J c -t behavior as a function of temperature ͑T͒ and applied magnetic field ͑H͒ in the thickness range that is within the modified Larkin length L c . It has been found that the J c -t behavior can be well described by the collective pinning ͑CP͒ model as monotonically decreasing J c ϳ t −1/2 when thermal assisted flux motion ͑TAFM͒ is suppressed at low T close to zero. TAFM becomes increasingly important at elevated temperatures and causes deviation of the J c -t from the CP model in the thickness range below the magnetic penetration depth. The deviation is more pronounced at smaller thickness and increases with T and H. Consequently, a completely reversed J c -t from monotonically decreasing to monotonically increasing occurs when TAFM dominates in high T and H ranges. This result suggests that the monotonic decreasing J c -t behavior is an intrinsic property of uniform YBCO films, while extrinsic effects such as material nonuniformity can greatly complicate it.The strong dependence of critical current density ͑J c ͒ on the thickness ͑t͒ of high-T c superconducting ͑HTS͒ films has presented a tough question that challenges our understanding of basic physics governing electric transport properties in HTS films. 1-5 Basically, J c measured at 77 K and self-field ͑SF͒ on films of HTS materials, such as YBa 2 Cu 3 O 7−x ͑YBCO͒, decreases monotonically with increasing film thickness. A basic question is whether this J c -t behavior is simply caused by material inhomogeneity through thickness or related to an intrinsic property of superconductors. It should be realized that the major J c reduction occurs in the thickness range below ϳ0.6 m, where microstructure degradation is not a major concern. Interestingly, the J c data reported on a large number of YBCO film samples 5-7 made with different techniques fall more or less on the curve of J c ϳ t −1/2 at 77 K and SF, which agrees with the prediction of weak collective pinning model ͑CP͒ for superconducting films thinner than the longitudinal collective pinning length L c ͑Larkin length͒. 8 In the CP model, a quantized magnetic flux line ͑FL͒ with a length of L Ͻ L c is rigid and cannot bend to accommodate different pinning centers nearby. When the dominant pinning centers are randomly distributed point defects, the pinning force ͑F p ͒ exerted on a FL scales as L 1/2 while the Lorentz force scales as L. This leads to the J c ϳ t −1/2 behavior. As L exceeds L c , the FL resumes its elasticity and bends itself to accommodate the pinning center, resulting in a thickness-independent J c .Although the CP model fits the SF J c -t relatively well at 77 K, some questions remain. The first question is about the order of magnitude of the L c . The original L c for a weak collective pinning system is calculated from L c Ϸ r p ͑J 0 / J c ͒ 1/2 , where r p is the pinning center interaction radius and J...

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“…However, when data are taken in a series of films or foils of variable thickness t, J c ͑defined as I c /Wt, where W is the foil width͒ is generally observed to increase with decreasing t. More precisely, Joiner and Kuhl 6 reported an exact linear dependence J c vs 1/t in PbBi foils. A similar behavior is retrieved in YBCO films, when the thickness is larger than about 2 ab , 7 for example, J c tϳ10 A/cm in the low-field limit at 70 K. 8 The fact that J c tϭconst in samples otherwise prepared in the same way could be immediately and most simply interpreted by stating that K c ϭI c /2Wϭconst.…”

Section: Introductionmentioning

confidence: 62%

Critical currents in the anisotropic superconductor2H−NbSe2:Evidence for an upper bound of the surface critical-current density

Lazard¹,

Mathieu²,

Plaçais³

et al. 2002

Phys. Rev. B

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According to the Mathieu-Simon continuum theory of the vortex state, a large nondissipative supercurrent can flow over a small depth from a rough surface, up to an easily estimated critical value K c (A/m) of the surface current density. It is shown that K c must saturate at high fields in an anisotropic crystal when the surface roughness is increased, and the corresponding upper bound only depends on fundamental parameters of the material. Measurements in 2H-NbSe 2 crystals confirm this saturation effect quantitatively, as well as the proposed idea that, in a large class of soft samples, the critical current should be entirely accounted for by surface K c currents.

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Magnetization and flux creep in thin YBa2Cu3O7−δ films of various thickness

Cited by 18 publications

References 21 publications

Strong pinning in high-temperature superconducting films

Strong pinning in high-temperature superconducting films

Effect of temperature and magnetic field on the thickness dependence of the critical current density ofYBa2Cu3O7−x
Wang
¹
,
Wu
²

2007
Phys. Rev. B
23
1
4
0
View full text Add to dashboard Cite

Critical currents in the anisotropic superconductor2H−NbSe2:Evidence for an upper bound of the surface critical-current density

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Magnetization and flux creep in thin YBa2Cu3O7−δ films of various thickness

Cited by 18 publications

References 21 publications

Strong pinning in high-temperature superconducting films

Strong pinning in high-temperature superconducting films

Effect of temperature and magnetic field on the thickness dependence of the critical current density ofYBa2Cu3O7−xWang1, Wu2 2007Phys. Rev. B23140View full textAdd to dashboardCite

Critical currents in the anisotropic superconductor2H−NbSe2:Evidence for an upper bound of the surface critical-current density

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Effect of temperature and magnetic field on the thickness dependence of the critical current density ofYBa2Cu3O7−x
Wang
¹
,
Wu
²

2007
Phys. Rev. B
23
1
4
0
View full text Add to dashboard Cite