The Theory of Cylindrical Magnetic Domains

The recent development of a technique for the propagation of isolated magnetic domains in an arbitrary direction in anisotropic ferromagnetic thin films by P. C. Michaelis created a renewed interest in the use of domain propagation for device purposes. 1 The technique used by Michaelis for propagating domains along the easy axis is quite different from that used for propagation along the hard axis. During discussions on the possible application of these techniques, A. H. Bobeck, U. F. Gianola, R. C. Sherwood, and W. Shockley suggested that for general symmetrical domain propagation the direction of magnetization must lie normal to the plane of the film2. The recognition that rare earth orthoferrites have the required properties came in response to this suggestion. 3 Experimental work on the application of this type of 3287 3314 TI-IE BELL SYSTEM TECHNICAL JOURNAL, DECEMBER 1969 domain motion device was then begun. Although at the present time this work has been largely concentrated on the orthoferrites, there exist other materials, such as the hexagonal ferrites and manganese bismuth, having the required properties. The present work directs attention to structures in which the properties of the material used require the magnetization to lie normal to the surface of the plate. The modes of operation of devices constructed from such structures are classified according to the effect of wall motion coercivity. In the case of very high wall motion coercivity, the application of shaped applied fields determines the initial domain configuration which is then maintained by coercivity.