Spin polarized tunneling and mixed spin states in the EuS conduction band

Abstract

Electron spin polarization and emission current from a W-EuS field emission experiment are discussed. A new theoretical model is presented, in which the EuS conduction band consists of pure spin states and mixed spin states, each weighted with a temperature dependent spectral weight (reduced density of states). They govern the tunnel process at the W-EuS interface (spin filter). It turns out that the polarizing effect of this spin filter is less than 100% at temperatures T below the Curie temperature of EuS, except at T = 0. Models, in which the conduction band consists of pure spin states only (spin up, respectively, spin down) fail to explain the spin polarization dependence on T, though they correctly describe the T dependent behavior of quantities, where the measurement averages over all spin directions, e.g. tunnel current density, absorption edge shift.