British Association Discussions: Magnetic Alloys and Problems of Metallic Structure

Abstract

THE general character of the variation of magnetization of ferromagnetics with field is well known. Different materials differ widely in their low-field characteristics, and in recent years there have been enormous advances in the production of materials with improved properties for particular technical applications. For permanent magnet materials, for example, the value of (BH)max on the demagnetization curve (a measure of the effectiveness, being approximately inversely proportional to the volume of material required to produce a given external field in a given volume) is greater by a factor of about 5 in the modern iron-nickel-aluminium alloys (developed since 1931) than in tungsten steel, the best permanent magnet material available twenty years ago. For 'soft' magnetic materials the improvements have been no less spectacular, notably through the development of iron-nickel alloys. For the most part, the improved materials have been the result of systematic empirical research. An understanding of the factors determinative of magnetic characteristics is, however, clearly desirable, not only from a purely scientific point of view, but also from the point of view of the control, and further development, of technically desirable properties. In this article a brief account is given of the present outlook on the general theoretical problems involved, and also of recent experimental work illustrative of the manner in which the fundamental problems may be attacked.