MAGNETIC PROPERTIES OF SUPERCONDUCTING NIOBIUM-TANTALUM ALLOYS

The superconducting transition temperature and isothermal magnetization have been measured for a series of Nb-Ta alloys ranging from Nb-13 at. % Ta to Nb-83 at. % Ta. These alloys are characterized as dirty type II superconductors; the electron mean free path l lies in a range from 0.1 ξ0 to 0.3 ξ0, where ξ0 is the intrinsic coherence length. The Ginzburg-Landau parameter κ takes the maximum value of 4.1 at the composition, Nb-50 at. % Ta. In concentrated alloys with compositions 20~80 at. % Ta, the temperature dependence of the generalized Ginzburg-Landau parameter κ1(T) accords with the theory for the dirty limit. Especially, the reduced parameter at 0°K, κ1(0)/κ, is in excellent agreement with the theoretical value 1.20. This agreement between experiment and theory is attributed to the fact that the temperature dependence of both the thermodynamic critical field Hc(T) and the upper critical field Hc2(T) follows the microscopic theory. © 1968, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.