Magnetic Bubble Materials

The bubble domain memory was first reported by Bobeck (1) in 1967. His concept was based on the fact that a cylindrical magnetic domain, that is, a small region of reversed magnetic polarity in an otherwise com­ pletely magnetized plate of material, is stable over a convenient range of applied field. The stable cylindrical domain can be moved in the plate under the influence of magnetic field gradients, or it can remain at rest in the plate under a modest uniform applied field. It was, in fact, the behavior of cylindrical domains when viewed through a polarizing micro­ scope under the influence of perturbing magnetic fields that led Bobeck to dub them "bubble domains." The literature on the behavior of mag­ netic bubbles and bubble domain memory design is now quite extensive (2-7) and is not discussed here, but two advantages of the bubble domain memory should be mentioned. First, since the bubble is stable in the pre­ sence of a small field that can be supplied by a permanent magnet, the bubble domain memory is nonvolatile; that is, the information in the memory is not lost when the power to the memory is off. Second,. the bubble diameter can be reduced to about one micrometer so the packing density for information can be quite high. Storage densities of a megabit per square centimeter are now seen in advanced engineering designs. From the standpoint of the materials scien tist, preparation of the memory element for a bubble domain device presents a many-faceted problem that extends over several technical fields. the materials scientist must have a good knowledge of the physics of'magnetic materials, as well as the chemistry of preparation of magnetic materials, bulk crysta:l growth