title: Size and shape dependence of thermal spin transitions in nanoislands.
abstract: Theoretical calculations of thermal spin transitions in nanoscale clusters on a surface are presented. The mechanisms for magnetization reversal are identified and the activation energy and pre-exponential factor for the rate are evaluated using a recently developed harmonic transition state theory and a Heisenberg-type Hamiltonian. A maximum is found in the pre-exponential factor as a function of cluster size corresponding to a crossover from a uniform rotation mechanism to temporary domain wall formation. As the islands grow, the energy barrier increases up to a limit where the domain wall is fully established. For larger islands, the minimum energy path becomes flat resulting in a significant recrossing correction to the transition state theory estimate of the rate. The parameters of the Hamiltonian are chosen to mimic Fe clusters on a W(110) surface, a system that has previously been studied extensively in the laboratory and the calculated results are found to be in close agreement with the reported measurements.
authors: Science Institute and Faculty of Science, VR-III, University of Iceland, 107 Reykjavík, Iceland.
authors: Pavel F
authors: PF
authors: Bessarab
authors: Valery M
authors: VM
authors: Uzdin
authors: Hannes
authors: H
authors: Jónsson