Chapter 3 - Spin-polarized tunneling

Abstract

This chapter focuses on spin-polarized tunneling in superconductors and ferromagnetic materials. The superconducting tunneling conductance technique is used for measuring the spin polarization of conduction electrons in a ferromagnetic material very different from 3d metals. Using a spin-split superconducting film remains the most unambiguous method of measuring the spin polarization of the tunnel current from a ferromagnetic metal because of the long coherence length of superconductors and the complete understanding of the theory and experimental method of superconducting tunnel spectroscopy. In spin-polarized tunneling, the polarization of the tunnel current is derived from the spin imbalance of the density of states of spin-up and spin-down conduction electrons at the Fermi energy. Spin-polarized tunneling between superconductors and ferromagnets show that the conduction electrons tunneling from ferromagnetic metals are spin polarized with degrees of polarization that are characteristic of each metal. The spin polarization of the tunnel current from ferromagnetic electrodes is extremely sensitive to surface and interface properties because of the short coherence length characteristic of the ferromagnetic state.