Tunneling conductance spectra of a metal/ferromagnet junction within a two-band model

Abstract

We present a theory based on a scattering matrix approach to explain the tunneling spectroscopy of a metal/ferromagnet junction. The isotropic one-band free electron model was used to describe the energy dispersion relation of the electrons in a metal layer, while two-band approximation was used to examine the electronic dispersion relation within the ferromagnetic material. s-band and d-band coupling were considered using the two-band approximation. In this work, interfacial spin-flip scattering was neglected. The energy dispersion and tunneling conductance spectra were calculated to study the effect of the coupling strength between the two bands. With no coupling, the energy band will have the crossing point between the bands. In contrast, a gap is opened up at the crossing points. It was found that the size of the gap depends on the coupling strength. Some kinks occurred in the energy band corresponding to the crossing points. The rich features of conductance spectra occurring in the metallic regime have the effects more significant than those occurring in the tunneling regime. In both regimes the conductance spectrum becomes largest if the effective mass of free electrons in the majority of the bands in the ferromagnetic material is approximately in the same order as that of the free electrons in metals.