A study of spin-dependent electron inelastic mean free path and spin excitations in ferromagnetic metals.

摘要

We explore the spin dependence of the inelastic mean free path of an excited electron and spin excitations in ferromagnetic transition metals. In chapter 1, we present simple one band Hubbard model calculations of the dependence of the inelastic mean free path (IMFP) on the spin direction and energy. The excited electron is assumed to reside in a plane wave state, while the metal electrons are modeled within the framework of a one band Hubbard model. We consider scattering by both Stoner excitations and by spin waves, and outline their relative importance in various energy ranges. In addition, we explore the dependence of the inelastic mean free path on the number of holes in the spin polarized energy bands of the substrate.; In chapter 2, we present explicit calculations based on the realistic model, for propagation in the bulk of the ferromagnetic metals Fe and Ni. The substrate electrons are modeled within the framework of an empirical tight binding description of the 3d, 4s and 4p bands combined with intra atomic Coulomb interactions between electrons in the 3d shell. The analysis of spin flip contributions to the inelastic mean free path incorporates the role of spin wave emission. We discuss the energy variation of the spin asymmetry in the mean free path, along with other issues. We find for electrons a few eV above the vacuum level that the mean free path of minority spin electrons is very short.; In chapter 3, we present theoretical calculations of the contribution to the spin polarized electron energy loss (SPEELS) spectrum of ferromagnetic Ni. We find, save for the wave vector transfer near the center of the Brillouin zone, the spin wave loss feature is obscured by low lying Stoner excitations, in contrast to Fe. Our calculations show that in inelastic neutron scattering studies of spin waves in Ni, the spin wave loss peak dominates. The physical reason for this difference is discussed.