Interpretation of High Coercivity in Ferromagnetic Materials

Abstract

In the generally accepted theory of the ordinary magnetization curves of ferromagnetics, due to Becker, Kersten and many others, and fully described by Becker and Doring1., coercivity is related to the amplitude of internal stress variations through their effect on domain boundary movement. Although there can be little doubt as to the correctness of the basic ideas, or to their wide applicability, the treatment cannot account for coercivities of 500 oersted, and more, which are obtained in modern permanent magnet materials, without arbitrary and improbable assumptions about the magnitude and character of the internal stress variations. It occurred to one of us some years ago that for those alloys of the dispersion-hardening type for which the higher coercivities are found, an entirely different type of explanation might be possible, and some preliminary calculations gave promising results. This line of inquiry was interrupted by the War, and no more than vague references to it have been published2, though it has been discussed verbally and in correspondence with others interested. A systematic attack on the problem was resumed at the beginning of 1946, and a full account of the work has now been prepared. In view of the inevitable delays in publication a brief account may be appropriate here. It may be stated quite frankly that the immediate stimulus to this communication has been two short and admirable papers by Néel³, which have just appeared, and which show that he has been thinking along similar lines with particular reference to powder magnets.