# Berlin 2015 – wissenschaftliches Programm

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# TT: Fachverband Tiefe Temperaturen

## TT 40: Electronic Structure of Magnetism, Micromagnetism, Computational Magnetism (organized by MA)

### TT 40.3: Vortrag

### Dienstag, 17. März 2015, 10:00–10:15, H 0112

**Navigation on the energy surface of the noncollinear Alexander-Anderson model using a magnetic force theorem** — •Pavel Bessarab^{1,2}, Valery Uzdin^{2,3}, and Hannes Jónsson^{4,5} — ^{1}Royal Institute of Technology KTH, Stockholm, Sweden — ^{2}St. Petersburg State University, St. Petersburg, Russia — ^{3}St. Petersburg National Research University of Information Technologies, Mechanics and Optics, St. Petersburg, Russia — ^{4}University of Iceland, Reykjavik, Iceland — ^{5}Aalto University, Espoo, Finland

Magnetic force theorem is derived within the multiple impurity, noncollinear Alexander-Anderson (NCAA) model - an important tool for efficient calculation of the total energy gradient with respect to orientation of magnetic moments, the magnetic 'forces'. Efficient evaluation of magnetic forces is of great importance for the large scale simulation of spin dynamics, minimization of the energy to identify stable and metastable magnetic states, or, in general, navigation on the energy surface of a magnetic system. NCAA model and magnetic force theorem are applied to calculate minimum energy paths between stable magnetic states of the monolayer Fe clusters on a W(110) surface, revealing complex mechanism of the magnetization reversal. Moreover, a noncollinear magnetic state is identified in a 7 x 7 atomic row Fe island where the magnetic moments are arranged in an antivortex configuration with the central ones pointing out of the (110) plane. The minimum energy path between this antivortex state and the collinear ground state is also calculated and the thermal stability of the antivortex state estimated.