Large Barkhausen Discontinuities and Their Propagation in Ni-Fe Alloys

The velocity of propagation of large Barkhausen discontinuities has been investigated as a function of circular field, longitudinal field, torsion and tension for a cold drawn 10 percent Ni-Fe alloy wire 0.0334 cm in diameter. Curves relating velocity of propagation and circular field were found to be similar to curves relating velocity of propagation and longitudinal field, thus suggesting that the functional relationship between velocity and circular field is identical with that between velocity and longitudinal field. These relationships were explained when it was found by two different experimental studies that only the component of the resultant field, impressed on the wire, in the direction of the principal strain axis of elongation is important in determining the velocity of propagation. The component perpendicular to this direction of maximum elongation produces no appreciable effect on the velocity. A method of heat treating 70 percent Ni-Fe alloy wire 0.0321 cm in diameter has been developed which made it possible to investigate the relationship between velocity of propagation and longitudinal field over much greater ranges of field and velocity than was possible for untreated wire. Over a range of field strengths of 2.23 oersteds the velocity was observed to vary from 1000 cm sec.^-1 to 140,750 cm sec.^-1. The relationship between velocity and field for this wire is definitely not linear. Discontinuities in which the change in induction was accurately equal to the total change in induction between saturation in the two directions were observed for these heat treated wires.