THE EFFECT OF THE ELECTRON-PHONON INTERACTION ON THE SPIN SPLITTING OF ELECTRON-ENERGY BANDS IN AN ITINERANT-ELECTRON FERROMAGNET

We report our discovery that the exchange splitting of the electron energy bands in the ferromagnetic state of a metal can be affected by the effect of the electron-phonon interaction and that, whereas the sign and magnitude of such a phonon effect depend sensitively on the electronic structure around the Fermi surface of the metal, the magnitude can be comparable with that of the ordinary Stoner exchange splitting. This conclusion was obtained by examining how the phonon frequencies, and therefore the phonon free energy, change with the spin splitting of the energy bands of the screening electrons in an itinerant electron ferromagnet. By carrying out a numerical calculation with a model electronic density of states, we demonstrate the importance of considering this effect in accounting for the observed magnetization and its temperature dependence in a ferromagnetic metal.