Spin-Polarized Scanning Tunneling Spectroscopy on Fe and Ni

This is a report of a spin-polarized spectroscopy study performed using a scanning tunneling microscope with Fe and Ni tips to probe the electronic structure of the levels involved in the tunneling junction. In these model experiments polarized electrons tunnel from the nanometer-sized apex region of the ferromagnetic tips into GaAs(110), which serves as an optical electron-spin detector. The spin-polarized tunneling spectra show qualitative agreement with the electronic structure of the filled 3d levels of the ferromagnets. Salient features observed include the following: (a) near the Fermi level the magnitude of the spin-polarization
determined from the measurements is larger than 60% for Ni; (b) at energies close to the Fermi level, the spin polarization is positive for Fe and negative for Ni; and (c) a sign reversal of the spin-polarization has been observed on Ni.