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Upper critical field measurements of the A15 type compounds Nb~3Au,Nb3Au0.7Pt0.3 and Nb3Pt having Tc values of 10.7, 13.0 and 8.7K, respectively, show Hc2(0) values of 235, 295 and 125 kG, respectively. The data for the compounds containing Au fit closely calculations for a dirty type II superconductor with no paramagnetic limiting, but data for Nb3Pt are slightly above these calculations. 相似文献
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The anisotropy of Hc2 for single crystal Nb3Sn and V3Si in the low temperature tetragonal phase was measured in high magnetic fields. At ~ 8K, δ = [Hc2[100]-Hc2[110])/Hc2] ≈0.05 for Nb3Sn and δ ≈ 0.02 for V3Si. The data do not show evidence of a highly anisotropic Fermi surface for Nb3Sn or V3Si. 相似文献
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Measurements of the upper critical field, Hc2(T), in single crystal Nb3Sn were extended to 30 tesla (300 kG) with dc fields produced by a Hybrid magnet. Observations of Hc2(T) were made for materials which remain in the cubic (c) phase and those which show a martensitic transformation at the tetragonal (t) phase. Hc2(T) measurements of Nb3Sn for a pure crystal for which the de Haasvan Alphen (DHVA) effect was observed and for polycrystalline (t) phase and (c) phase materials are also reported. Measured values of Hc2(4.2 K) and calculated values of Hc2(0) are: 1) along the [100] direction for our earlier Nb3Sn, Hc2(4.2 K) = 26 T for the (c) phase and 21.5 T for the (t) phase; Hc2(0) = 29T for the (c) phase and 24 T for the (t) phase; 2) along the [100] direction for the DHVA material Hc2(4.2 K) = 18 T and Hc2(0) = 20 T; 3) for polycrystalline Nb3Sn (t) phase material Hc2(4.2 K) = 23 T and Hc2(0) = 25 T and for (c) phase material Hc2(4.2 K) = 26 T and Hc2(0) = 29 T. The values of (dHc2/dT)T=Tc vary from 2.4T/K for the highest Hc2(T) material to 1.6T/K for the DHVA material. The anisotropy for various Nb3Sn single crystal materials is small and independent of temperature from Tc to 0.1 Tc. δTc between the (c) and (t) phase is <0.3 K. Within experimental error excellent fits of Hc2(T) with theory are obtained assuming a dirty or clean Type II superconductor with no Pauli paramagnetic limiting. Experimental details and strong-coupling effects are discussed. When strong-coupling is included, the effects of any paramagnetic limiting would be small and not detectable within our present experimental error. Brief comments also are made concerning Hc2 of V3Si. 相似文献
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