Properties of proximity effect and filament coupling in NbTi wires

Filament coupling induced by the proximity effect was studied through AC susceptibility measurements an Cu-matrix NbTi multifilamentary wires. The sample wires having different interfilamentary spacings ranging from 0.35 to 1.04 /spl mu/m and various twist pitches were prepared from the VAMAS (Versailles Project on Advanced Materials and Standards) reference sample H-1, which has a filament number of 931. The measurements were carried out in each of the two different field directions, parallel and perpendicular, to the wire axis. It has been found that the value of perpendicular field to suppress the proximity effect coupling is two orders of magnitude larger than that of the parallel field. In the perpendicular field, the twist of the wires affects the occurrence of the coupling: the filaments couple at higher temperature and higher field with longer twist pitch. On the contrary, the twist pitch dependence of the coupling has not been observed in a parallel field. In addition, the effect of transport current on the coupling has been examined.>