Propagation of Large Barkhausen Discontinuities

Large Barkhausen discontinuities have previously been observed by Forrer and by Preisach in nickel wires and hard-drawn wires of the nickel-iron series respectively under stress. A prediction that these discontinuities occur in form of a propagation along the wire, starting at a nucleus, has now been substantiated. In the experiments an additional local field was used to start the propagation at a definite point on the wire, which was in a uniform magnetic field, and the velocity was determined by measuring the short time interval elapsing between the passage through two search coils around the wire. With a fixed value of tension on the wire, the velocity $v$ was found to vary approximately linearly with the applied uniform field $H$, so that $v=A(H-H_0)$. $A$ is the slope of the velocity-field characteristic and $H_0$ is called the critical field. Measured velocities range from 500 to 40,000 cm ${\sec }^{-1\mathrm{}}$. $H_0$ varies with composition, amount of cold working, and with the stress applied to the wire. Increasing tension reduces the critical field over the greater part of the Ni-Fe alloy composition range. The behavior of $H_0$ with increasing and decreasing tension shows the presence of elastic hysteresis. $A$ is nearly constant for changes in tension, in diameter of wire, for composition of wire, and is the same for a strip. Its value is approximately 25,000 cm ${\sec }^{-1\mathrm{}}$ ${\mathrm{gauss}}^{-1\mathrm{}}$.