Magnetism of iron on tungsten (001) studied by spin-resolved scanning tunneling microscopy and spectroscopy

The system of Fe on W(001) has been investigated using spin-integrated as well as spin polarized scanning tunneling microscopy and spectroscopy. The electronic structure in the pseudomorphic growth regime and the beginning of strain relief has been studied and a pronounced layer dependence of the differential conductance has been observed. The spin-resolved measurements focus on the magnetic structure in the pseudomorphic regime. The domain structure is investigated with high spatial resolution and the fourfold anisotropy can directly be deduced from the maps of differential conductance. Quantitative analysis of the intensity of the signal reveals a layer dependent easy axis in the pseudomorphic regime. While the second and third monolayer are magnetized along ⟨110⟩ directions of the surface the fourth monolayer has an easy axis along ⟨100⟩. These high-symmetry directions and therefore also the layer-dependent easy axes enclose an angle of 45°.