Magnetic Energy Formulas and their Relation to Magnetization Theory

Present theories of magnetization are based largely on energy formulas. These are incomplete because they rely on a calculation of magnetization work in the absence of strain and of strain work in the absence of magnetization. The present paper summarizes and relates to magnetization theory a calculation, already published elsewhere, in which magnetization and strain are assumed from the start to be present simultaneously; furthermore forces are calculated directly, without use of energy arguments until the properties special materials are considered. An important result is that the separation of the force on part of a body into a "magnetic" force and a force derivable from "stresses" can be accomplished in more than one way. the theory confirms the traditional results for fluids; but for elastic solids, it yields terms not present in the formulas of the traditional theory. These terms may be important in the magnetization process. For a uniformly magnetized ellipsoid they lead to a nonuniform magnetostriction "form effect" with a mean strain equal to the strain calculated by Becker.