NDLI: Unexpected effect of field angle in magnetoresistance measurements of high-purity Nb

Content Provider	IEEE Xplore Digital Library
Author	Goodrich, L.F. Stauffer, T.C. Splett, J.D. Vecchia, D.F.
Copyright Year	2002
Abstract	We report on unexpected field-angle dependence of magnetoresistance measurements of commercial, high-purity Nb discovered during our study of residual resistivity ratio (RRR) measurements. The RRR value indicates the purity and the low-temperature thermal conductivity of the Nb and is used as a specification for superconducting radio-frequency cavities. The RRR is typically defined as the ratio of the electrical resistivities measured at 273 K and 4.2 K. One way to obtain the normal-state resistivity at 4.2 K is to measure the resistivity versus magnetic field at 4.2 K and extrapolate to zero field. The field-angle dependence was measured when a specimen was rotated while the field was transverse to the specimen current. The resistance changed by about 10% as the angle varied at 8 T and the local maxima and minima of the resistance were separated by about 30/spl deg/. This was observed on three polycrystalline Nb bar specimens with nominal dimensions of 64 mm /spl times/ 6.7 mm /spl times/ 3.3 mm and voltage taps separated by 30 mm. A similar field-angle dependence was obtained on a polycrystalline Cu wire specimen. This phenomenon has implications for Nb RRR measurements and interlaboratory comparisons.
Sponsorship	Council on Superconductivity Appl. Superconductivity Conference Inc MIT
Starting Page	3616
Ending Page	3619
Page Count	4
File Size	132729
File Format	PDF
ISSN	10518223
Volume Number	15
Issue Number	2
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2005-06-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Magnetoresistance Magnetic field measurement Goniometers Niobium Thermal conductivity Electric variables measurement Electrical resistance measurement Radio frequency Electric resistance Current measurement superconductor Angular dependence niobium residual resistivity ratio resistance measurement
Content Type	Text
Resource Type	Article
Subject	Condensed Matter Physics Electronic, Optical and Magnetic Materials Electrical and Electronic Engineering

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