Transport critical current density and dimensional crossover in superconducting Nb/NbZr multilayers

Nojima, Tsutomu; Kinoshita, Masayuki; Nakano, Shigeru; Kuwasawa, Y.

doi:10.1016/0921-4534(93)90538-2

Cited by 16 publications

(9 citation statements)

References 12 publications

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“…Measurements of the twist-pitch dependence of the magnetization for multifilament Nb-Ti/Cu composites which are in agreement with Eq. ͑8͒ have been obtained by Akune et al 49 Since we did not observe the anomalous behavior of H c2 (T) which is seen in multilayer Nb/Nb-Ti and Nb/Nb-Zr having equal Nb and Nb-alloy thicknesses, 50,51 we conclude that the nucleation of superconductivity always occurs within the Nb47Ti matrix, 43,52 even when both the pin and superconductor thicknesses are much less than N . Thus the results of Mota et al for proximity-coupled Cu and Ag should also be valid for Nb1Ti, even when the applied field is below the upper critical field of the Nb1Ti pins and when the pin thickness and separation are less than N .…”

Section: B Pinning By Planar Defects With Nonzero Thicknesssupporting

confidence: 57%

Flux-pinning mechanism of proximity-coupled planar defects in conventional superconductors: Evidence that magnetic pinning is the dominant pinning mechanism in niobium-titanium alloy

1996

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We propose that a magnetic pinning mechanism is the dominant flux-pinning mechanism of proximitycoupled, planar defects when the field is parallel to the defect. We find compelling evidence that this pinning mechanism is responsible for the strong flux-pinning force exerted by ribbon-shaped ␣-Ti precipitates and artificial pins in Nb-Ti superconductors, instead of the core pinning mechanism as has been hitherto widely believed. Because the elementary pinning force f p (H) is nonmonotonic when it is optimum ͑i.e., when the defect thickness t and the proximity length N have comparable dimensions͒, the total pinning force F p (H) generally does not show temperature scaling. Characteristic changes in the magnitude and shape of F p (H) at constant T but at different t/ N ͑e.g., different Nb-Ti wire diameters͒ are also direct consequences of the pinning mechanism. The optimum flux-pinning state is a compromise between maximizing f p and getting the highest number density of pins. For a given defect composition this state is reached when tϳ N /3, while for varying defect composition the peak F p gets higher when N is made shorter. Artificial pinning center Nb-Ti wires having short N pins appear to be vital for obtaining high J c at high fields because only then is the elementary pinning force optimized at small pin thicknesses which permit a high number density of vortex-pin interactions and a large bulk pinning force. We find verification of our predictions in experimental F p (H,T,t) data obtained on special laboratory-scale artificial pinning-center Nb-Ti wires.

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Section: B Pinning By Planar Defects With Nonzero Thicknesssupporting

confidence: 57%

Flux-pinning mechanism of proximity-coupled planar defects in conventional superconductors: Evidence that magnetic pinning is the dominant pinning mechanism in niobium-titanium alloy

1996

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“…Nojima et al [6] have suggested that a possible mechanism is the transition from proximity-coupled Nb layers (through the Nb-alloy) to decoupled Nb layers, which they claim occurs at B, (see Figs. 2 and 3).…”

Section: Resultsmentioning

confidence: 96%

“…Since &2 (8) and J, (8) have cusps at 0 ' [41- [6], we moved intentionally away from true parallel to reduce systematic errors due to possible misalignment.…”

Section: Sample Fabrication Andmentioning

confidence: 99%

“…There has been renewed interest in the properties of layered metallic superconductors in recent years, both in their upper critical field [11-[41 and critical current behavior [5], [ 6 ] , mostly because of their analogous smcture to high Tc compounds. Our work focuses on understanding (and improving) flux pinning in NbTi wires--especially wire using artificial pinning centers (APCs) [7], [8].…”

Section: Introductionmentioning

confidence: 99%

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Flux pinning in NbTi/Nb multilayers

McCambridge

Rizzo

Ling

et al. 1995

IEEE Trans. Appl. Supercond.

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We made thin film-multilayers of NbTi and Nb (dmTi = 20 nm and dNb = 3-9 nm). samples were characterized by electrical transport measurements between 4.2 K and T,, in magnetic fields up to 6 T. We present Jc as a function of the device geometry and orientation of the field. For some multilayers, Jc had a large peak whose onset occurs near * 0.2 He2. We suggest this peak effect is caused by a softening of the tilt modulus. Measured critical current densities at 4.2 K of 16 kA/mm2 at 3 T and 8 kA/mm2 at 5 T are among the highest achieved in the NbTi system.

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“…Reviews of experimental studies of flux pinning in multilayers are given in Ref. [6,7]. Since the increase of J, in the peaks can reach 100% at high fields [5], understanding the nature of this effect and the ability to control it are of great practical importance.…”

Section: Introductionmentioning

confidence: 99%

Multiple peaks in the angular and field dependence of the critical currents in Nb-47wt%Ti/Cu multilayers

Kadyrov

Cooley

Gurevich

et al. 1997

IEEE Trans. Appl. Supercond.

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The effect of Nb-Ti layer thickness d, on the angular and field dependencies of J, in Nb-47wt.% TVCu multilayers was investigated. J, exhibits several peaks in the field and angular dependencies for superconductor and pin layer thickness comparable to the coherence and proximity lengths. The shape of the J,(B) curve strongly depends on the thickness of Nb-Ti layer. A single peak is present for d, > 10 nm and multiple peaks (two and three) are observed in a sample with ds :=lo nm. The low field peak is temperature independent, while the high-field peaks have a pronounced temperature dependence. We suggest that a crossover between dominant pinning mechanisms and orientational transitions in the vortex lattice is responsible for the observed behavior of J,(B).

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Transport critical current density and dimensional crossover in superconducting Nb/NbZr multilayers

Cited by 16 publications

References 12 publications

Flux-pinning mechanism of proximity-coupled planar defects in conventional superconductors: Evidence that magnetic pinning is the dominant pinning mechanism in niobium-titanium alloy

Flux-pinning mechanism of proximity-coupled planar defects in conventional superconductors: Evidence that magnetic pinning is the dominant pinning mechanism in niobium-titanium alloy

Flux pinning in NbTi/Nb multilayers

Multiple peaks in the angular and field dependence of the critical currents in Nb-47wt%Ti/Cu multilayers

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