THE ROLE OF THE ELECTRON-PHONON INTERACTION IN THE ANOMALOUS VOLUME AND ELASTICITY BEHAVIOR OF AN ITINERANT-ELECTRON FERROMAGNET

The principal objective of this paper is to show that the long puzzling, anomalous volume and elasticity behaviors of some itinerant electron ferromagnets, which are called Invars, can be understood if we consider the effects of the electron-phonon interaction. Such a novel role of phonons originates from the fact that phonon frequency of a metal depends on magnetization, as well as volume, of the metal. We point out how our conclusion is supported by the recent observation of negative Gruneisen constants in an Invar system, Fe-Pt, by Manosa et al. [J. Phys.: Condens. Matter 3, 2273 (1991)]. in the course of such study, we obtain interesting new results also on the joint effects of the electron-phonon interaction and the magneto-volume interaction on other fundamental physical quantities, such as magnetic susceptibility, magnetic expansivity, compressibility, pressure dependence of magnetization, and temperature dependence of magnetization, in addition to thermal expansion coefficient, of an itinerant electron ferromagnet.