Spin Polarization of Electrons Tunneling from Films of Fe, Co, Ni, and Gd

Abstract

The spin polarization of electrons tunneling from films of Fe, Co, Ni, and Gd to superconducting Al films is determined from conductance measurements. The phenomenological theory of superconducting-normal-metal tunneling is modified to describe superconducting-ferro-magnetic tunneling in a magnetic field. The experimental technique and the method of analysis of the conductance curves to obtain the electron polarization are both described. The observed polarization is positive (majority spin direction predominating) for all the metals; the values obtained were Fe, +44%; Co, +34%; Ni, +11%; and Gd, +4.3%.