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Unexpected Effect of Field Angle in Magnetoresistance Measurements of High-Purity Nb



Loren F. Goodrich, Theodore C. Stauffer, Jolene Splett, Dominic F. Vecchia


We report on unexpected field-angle dependence of the 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'. This was observed on three polycrystalline Nb bar specimens with nominal dimensions of 64 mm × 6.7 mm × 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.
IEEE Transactions on Applied Superconductivity


Angular dependence, cryogenics, niobium, residual resistivity ratio, resistance measurement, superconductor


Goodrich, L. , Stauffer, T. , Splett, J. and Vecchia, D. (2005), Unexpected Effect of Field Angle in Magnetoresistance Measurements of High-Purity Nb, IEEE Transactions on Applied Superconductivity, [online], (Accessed April 14, 2024)
Created May 31, 2005, Updated October 12, 2021