Abstract. -Energy dissipation is studied for a hard magnetic tip that scans a soft magnetic substrate. The dynamics of the atomic moments are simulated by solving the Landau-LifshitzGilbert (LLG) equation numerically. The local energy currents are analysed for the case of a Heisenberg spin chain taken as substrate. This leads to an explanation for the velocity dependence of the friction force: The non-linear contribution for high velocities can be attributed to a spin wave front pushed by the tip along the substrate.Introduction. -On the macroscopic scale the phenomenology of friction is well-known. However, investigations of energy dissipation on the micron and nanometer scale have led in recent years to many new insights [1]. This progress was made possible by the development of modern surface science methods, in particular Atomic Force Microscopy, which allows to measure energy dissipation caused by relative motion of a tip with respect to a substrate.Studies concerning the contribution of magnetic degrees of freedom to energy dissipation [2, 3] form a young subfield of nanotribology, which has been attracting increasing interest in recent years. Two classes of models have been considered, which show different phenomena. The first one is Ising-like spin systems with two equivalent half spaces moving relative to each other [4][5][6][7][8]. In this case, friction is induced by thermal fluctuations, and hence is not present at zero temperature. In the second class of models [9][10][11][12][13], there is no symmetry between slider and substrate: The slider, representing e.g. the tip of a Magnetic Force Microscope, interacts only locally with a planar magnetic surface. While scanning the surface, the tip in general excites substrate spins and hence experiences friction, even at zero temperature. The present study belongs to the second class of models.We investigate the nature of the substrate excitations caused by the tip motion for a classical Heisenberg model with Landau-Lifshitz-Gilbert (LLG, [14,15]) dynamics (precession around, and relaxation into the local field di-