Magnetic bubbles and their observation in the electron microscope

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Abstract
In favourable circumstances magnetic domains can be made to move very rapidly through a ferromagnetic material in response to an applied magnetic field. Recently this phenomenon has been exploited in a novel situation where cylindrical magnetic domains or magnetic ‘bubbles’ are used to store and manipulate information in a binary form. Because of their small size and high mobility bubbles may be arranged to form a memory which has a high storage density and which can be quickly accessed. In recent years much effort has gone into developing suitable materials to support these bubbles and into the design of optimum device configurations. Obviously there have been many accompanying investigations into the physics of bubble domains and methods of observing them. One of the important observational techniques, particularly for small bubbles, is electron microscopy which gives information on bubble structure which is unobtainable by any other method. This review seeks first to explain what magnetic bubbles are, secondly to discus briefly suitable materials and the workings of bubble devices and finally to outline the theory of observing bubbles in the electron microscope and the results of some experimental observations.