Dependence of critical current densities in composite conductors with ultrafine filaments on the magnetic field application

Critical current densities of Nb/sub 3/Sn composite conductors with ultrafine filament (d/sub f/=36.7 nm approximately 145 nm) have been observed to depend on the magnetic history of the composite. Magnetic fields were applied as follows. (A) (1) The bias field is increased to higher values and then reduced to B/sub 0/, (2) the bias field is increased directly from zero to B/sub 0/; and (3) the composite is cooled down within B/sub 0/. (B) After establishing B/sub 0/, a second field B/sub m/ is temporarily superimposed parallel or antiparallel to B/sub 0/ and then removed. Then the critical current density is measured by increasing the current. A new cycle of B/sub m/ of the same sign may follow, with the process being repeated.