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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 1012 A/m2 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. [ABSTRACT FROM AUTHOR]

In micromagnetic simulations, the magnetization in one simulation cell is acted upon by the demagnetization field that is generated by all simulation cells. In simulations with periodic boundary conditions, this leads to an infinite number of interactions that have to be taken into account. A method is presented that allows for an accurate calculation of the demagnetization tensor with one and two-dimensional periodic boundary conditions using a small amount of computation time. The method has been implemented in a micromagnetic simulation tool. For a reasonable accuracy and two-dimensional periodic boundary conditions the presented method is about six orders of magnitude faster than the straightforward method in which all cells beyond a certain distance are neglected. [ABSTRACT FROM PUBLISHER]

The future of nanoscale spin-based technologies hinges on a fundamental understanding and dynamic control of atomic-scale magnets. The role of the substrate conduction electrons on the dynamics of supported atomic magnets is still a question of interest lacking experimental insight. We characterized the temperature-dependent dynamical response of artificially constructed magnets, composed of a few exchange-coupled atomic spins adsorbed on a metallic substrate, to spin-polarized currents driven and read out by a magnetic scanning tunneling microscope tip. The dynamics, reflected by two-state spin noise, is quantified by a model that considers the interplay between quantum tunneling and sequential spin transitions driven by electron spin-flip processes and accounts for an observed spin-transfer torque effect. [ABSTRACT FROM AUTHOR]