Spin-Dependent Tunnelling from Transition-Metal Ferromagnets

Abstract

Spin-dependent tunnelling from ferromagnetic Ni, Co, and Fe, is theoretically examined and it is shown that the tunnelling current is predominantly due to $s$ electrons, despite the much greater density of $d$ states in these metals. $s-d$ hybridization leads to a positive (parallel to the majority $d$ electrons) polarization within ordinary Stoner (Hartree-Fock) theory, and it was found that it was insufficient to explain the experiment. However, if the self-energy due to spin-wave emission is included, good agreement with experiment for reasonable parameters was obtained. Hence, it is concluded that the band-theoretical description of the magnetism of these metals is compatible with the recent experiments of Tedrow and Meservey, provided that the dominant many-body effects are properly taken into account.