Quantitative description of a very high critical current density Nb-Ti superconductor during its final optimization strain. II. Flux pinning mechanisms

Journal Article · Fri Dec 15 04:00:00 EST 1989 · Journal of Applied Physics; (USA)

DOI:https://doi.org/10.1063/1.343625· OSTI ID:7268940

Meingast, C; Larbalestier, D C ^[1]

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1. Applied Superconductivity Center, University of Wisconsin-Madison, Madison, Wisconsin 53706 (US)

Flux pinning by {alpha}-Ti precipitates has been studied in a carefully made Nb 48 wt. % Ti composite having very high critical current density and a macroscopically rather uniform precipitate array. The pinning was studied as a function of field (0--15 T) and temperature (2.3 K---{ital T}{sub {ital c}}) for a ratio of the precipitate thickness ({ital t}{sub ppt}) and the coherence length ({xi}) which was varied between 10 and 0.1 by a large drawing strain. Surprisingly, the maximum bulk pinning force ({ital F}{sub {ital p}}) occurred for {ital t}{sub ppt}/2{xi}{approx equal}0.1 and a precipitate spacing about one-eighth the fluxon spacing, suggesting that the flux pinning occurs at clusters of precipitates. In contrast to earlier studies, strict temperature scaling of {ital F}{sub {ital p}} was not observed; the peak of the pinning force shifted to lower reduced fields as the temperature increased. The effect was largest for the finest scale microstructure. This nonscaling is interpreted in terms of two pinning mechanisms having different field and temperature dependencies. At low reduced fields, and at temperatures close to {ital T}{sub {ital c}}, the core interaction ({delta}{ital H}{sub {ital c}}) dominates. At higher reduced fields and low reduced temperatures, pinning due to variations in {kappa} also contributes to {ital F}{sub {ital p}}. Clusters of very fine {alpha}-Ti ribbon precipitates give rise to these variations in {ital H}{sub {ital c}} and {kappa}. A comparison of the specific pinning force with the core interaction model was made close to {ital T}{sub {ital c}}, where the {delta}{ital H}{sub {ital c}} pinning mechanism dominates. Good agreement was obtained for all precipitate thicknesses, indicating that the pinning can be quantitatively described by the core interaction and the direct summation models.

• OSTI ID: 7268940
• Journal Information: Journal of Applied Physics; (USA), Journal Name: Journal of Applied Physics; (USA) Vol. 66:12; ISSN 0021-8979; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
656100 -- Condensed Matter Physics-- Superconductivity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALLOYS
CRITICAL CURRENT
CURRENTS
ELECTRIC CURRENTS
ELEMENTS
MAGNETIC FIELDS
MAGNETIC FLUX
METALS
NIOBIUM ALLOYS
PRECIPITATION
PROXIMITY EFFECT
SCALING LAWS
SEPARATION PROCESSES
SUPERCONDUCTORS
TEMPERATURE DEPENDENCE
TITANIUM
TITANIUM ALLOYS
TRANSITION ELEMENTS
ULTRALOW TEMPERATURE