Barkhausen Effect. III. Nature of Change of Magnetization in Elementary Domains

Abstract

Transverse Barkhausen effect. It is found that the small sudden changes in magnetic moment which take place when material is magnetized, have components perpendicular as well as parallel to the direction of the magnetic field. Quantitative measurements of the transverse and longitudinal effects (changes in moment perpendicular and parallel to the direction of the field) show that the longitudinal effect is the larger when the magnetization is small and that the transverse effect is larger when the magnetization is large. Materials examined are (polycrystalline) annealed iron, hard-worked iron, and perminvar.Domain theory of ferromagnetism. The results are interpreted in terms of the domain theory, according to which ferromagnetic materials consist of small regions or domains always magnetized to saturation. Changes in magnetization are accomplished only by changes in the directions of magnetization in the domains. Sudden changes from one to another of the natural directions of magnetization in the crystal give rise to the Barkhausen effect, and in general have definite transverse and longitudinal components, the former now observed for the first time. The experiments show that when the gross magnetization (that of the substance as a whole) is small, the application of an additional magnetic field causes reversal of the direction of magnetization in the domains for which this direction was initially nearly antiparallel to the field. Experiments on annealed iron with high gross magnetization indicate, on the contrary, that the direction of magnetization in a domain may be altered through 90\ifmmode^\circ\else\textdegree\fi{}.