Magnetic Reversal Nuclei. Part V. Propagation of Large Barkhausen Discontinuities

In a Ni-Fe wire in which a preferred direction of magnetization is created by application of tension, stable regions of antisaturated magnetization can be produced by short application of high local fields. These nucleus regions will not grow after removal of the local field, although the direction and magnitude of the uniform external field favors growth. This is explained by the fact that their demagnetizing field lowers the total field in the neighborhood below the value $H_0$, which in former papers was recognized to be the minimum field value at which propagation would proceed spontaneously. Propagation will start from a nucleus region if the external field is raised to a value $H_S^{}{}_{}{}^{\prime }$, where $H_S^{}{}_{}{}^{\prime }$ has to fulfill the condition: $H_S^{}{}_{}{}^{\prime }=H_0+H_d$. $H_d$, the demagnetizing field of the nucleus, was calculated from its dimensions. The approximate size of a natural nucleus in a stressed wire was determined from the starting field $H_S$ of that wire; it had a length of a few mm and a diameter of several $\mu$.