Spin-polarized vacuum tunneling into the exchange-split surface state of Gd(0001)

Spin-polarized tunneling is demonstrated on Gd(0001) thin films using ferromagnetic probe tips in a low-temperature scanning tunneling microscope. The magnetic field dependent asymmetries in the differential tunneling conductivity are found at bias voltages which correspond to the energies of the spin components of the exchange-split Gd(0001) surface state. Maps of the spatial variation of the asymmetry reveal the magnetic structure of Gd(0001) thin films with a lateral resolution better than 20 nm. It is found that magnetic tip coatings thicker than 100 monolayers Fe may modify the sample domain structure due to the stray field of the tip.