Femtosecond laser irradiation is used to excite adsorbed CO molecules on a Cu110 surface; the ensuing motion of individual molecules across the surface is characterized on a site-to-site basis by in situ scanning tunneling microscopy. Adsorbate motion both along and perpendicular to the rows of the Cu110 surface occurs readily, in marked contrast to the behavior seen for equilibrium diffusion processes. The experimental findings for the probability and direction of the molecular motion can be understood as a manifestation of strong coupling between the adsorbates' lateral degrees of freedom and the substrate electronic excitation produced by the femtosecond laser radiation.

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The spin-transfer torque between itinerant electrons and the magnetization in a ferromagnet is of fundamental interest for the applied physics community. To investigate the spin-transfer torque, powerful simulation tools are mandatory. We propose a micromagnetic standard problem including the spin-transfer torque that can be used for the validation and falsification of micromagnetic simulation tools. The work is based on the micromagnetic model extended by the spin-transfer torque in continuously varying magnetizations as proposed by Zhang and Li. The standard problem geometry is a permalloy cuboid of 100 nm edge length and 10 nm thickness, which contains a Landau pattern with a vortex in the center of the structure. A spin-polarized dc current density of 10 12 A/m 2 flows laterally through the cuboid and moves the vortex core to a new steady-state position. We show that the new vortex-core position is a sensitive measure for the correctness of micromagnetic simulators that include the spin-transfer torque. The suitability of the proposed problem as a standard problem is tested by numerical results from four different finite-difference and finite-element-based simulation tools.

The strength of the non-adiabatic spin torque is currently under strong debate, as its value differs by orders of magnitude as well in theoretical predictions as in measurements. Here, a measurement scheme is presented that allows to determine the strength of the non-adiabatic spin torque accurately and directly. Analytical and numerical calculations show that the scheme allows to separate the displacement due to the Oersted field and is robust against uncertainties of the exact current direction. PACS numbers: 75.60.Ch, 72.25.Ba A spin-polarized current flowing through a ferromagnetic sample interacts with the magnetization and exerts a torque on the local magnetic moments. For conduction electron spins that follow the local magnetization adiabatically it has been shown that the interaction via spin transfer can be described by adding a current-dependent term to the Landau-LifshitzGilbert equation.[1] This equation has been extended by an additional term that takes the non-adiabatic influence of the itinerant spins into account.[2] Theoretically, several mechanisms have been proposed as the origin of the non-adiabatic spin torque, leading to different orders of magnitude for its strength. [2,3,4,5,6] Thus a precise measurement of the non-adiabatic spin torque is necessary to give insight into its microscopic origin. A determination of its strength is further important for a reliable prediction of the current-driven domain-wall velocity. [2] Currently measured values of the non-adiabatic spin torque for permalloy differ by one order of magnitude, [7,8,9,10] thus the strength of the non-adiabatic spin torque is under strong debate. In these experiments the observed motion of a domain wall was compared with micromagnetic simulations to determine the non-adiabatic spin torque. This analysis is highly susceptible to surface roughness and Oersted fields.Due to its high symmetry and spacial confinement a vortex in a micro-or nanostructured magnetic thin-film element is a promising system for the investigation of the spin-torque effect. [11,12,13] Vortices are formed when the in-plane magnetization curls around a center region. In this few-nanometerlarge center region, called the vortex core, the magnetization turns out of plane to minimize the exchange energy. There are four different ground states of a vortex. These states are labeled by the direction of the out-of-plane magnetization, called polarization p, and the sense of rotation of the in-plane magnetization, called chirality c. Polarizations of p = 1 and p = −1 denote a core that points parallel or antiparallel to the z axis, respectively. A chirality of c = 1 denotes a counterclockwise curling of the in-plane magnetization while c = −1 denotes a clockwise curling.It is known that vortices are displaced from their equilibrium position when excited by spin-polarized electric current pulses. [12,13,14,15,16,17,18,19,20] The spatial confinement of the vortex core within the film element yields an especially accessible system for measurements with scanning probe...