The effect of magnetic impurities and barriers on the magnetization and critical current of fine filament NbTi composites

It is known that the highest critical currents in fine-filament NbTi conductors are obtained when the filaments are closely spaced. However, the filaments in a composite with a high-parity copper matrix tend to be coupled via the proximity effect as the filament spacing is reduced leading to large magnetization at low fields. To reduce the proximity coupling, trial billets of NbTi were fabricated with Cu-30% Ni matrix, Cu-0.5% Mn matrix and one with a Ni barrier around the filaments. Wires drawn from these billets have shown that this interfilament coupling can be suppressed for very-small filament separations. A full-sized commercial billet with Cu-0.5% Mn matrix demonstrated that high-critical-current-density conductors with filament size approximately 1-5 mu m can be fabricated which show no interfilament coupling at low fields.