Investigation of the elementary excitations at oxide surfaces is of great importance to understand the spin- and lattice-dynamics in complex oxide materials. We have investigated the spin dependence of surface excitations on p(1x1)-O/Fe(001).  Surprisingly, we observed that the vibration excitations show a large spin asymmetry up to 90%. Systematic analysis of the inelastic electron scattering in the specular and off-specular geometries enabled us to separate the spin-dependent and spin-independent excitations [1]. Figure 4 shows the dispersion relation of all low-energy elementary surface excitations. We observed 4 different phonon modes and a magnon mode. The observed phonon modes can be well described by means of ab initio calculations.

Fig. 4: Dispersion relation of phonons and magnons on p(1x1)-O/Fe(001). The theoretically calculated phonon spectral densities projected on (a) the oxygen layer and (b) the topmost Fe layer are shown as color plot. Open (filled) symbols represent the experimental phonon (magnon) branches. Letters denote the displacement directions.