Spin-polarized vacuum tunneling: Correlation of electronic and magnetic properties on the nanometer scale

The realization of spin-polarized vacuum tunneling is demonstrated for the Gd(0001) surface, which is ideally suited since it exhibits a surface state that is exchange-split into two parts with opposite spin polarization. Bot h appear as distinct features in the tunneling spectra. The use of ferromag netic probe tips leads to magnetic-field-dependent asymmetries in the diffe rential tunneling conductivity at bias voltages which correspond to the ene rgies of the spin components. By mapping the asymmetry parameter we can ima ge the magnetic domain structure of the sample. The spin polarization of th e differential tunneling conductivity is found to be in excellent agreement with (inverse) photoemission data.