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Zeitschrift für Physikalische Chemie

International journal of research in physical chemistry and chemical physics

Editor-in-Chief: Rademann, Klaus

12 Issues per year


IMPACT FACTOR 2016: 1.012

CiteScore 2016: 0.99

SCImago Journal Rank (SJR) 2016: 0.463
Source Normalized Impact per Paper (SNIP) 2016: 0.470

Online
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2196-7156
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Volume 227, Issue 9-11

Issues

Potential Energy Surfaces and Rates of Spin Transitions

Pavel F. Bessarab / Valery M. Uzdin
  • National Research University of Information Technologies, Mechanics and Optics, St. Petersburg, 197101, Russia
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Hannes Jónsson
Published Online: 2013-07-08 | DOI: https://doi.org/10.1524/zpch.2013.0403

Abstract

The stability of magnetic states and the mechanism for magnetic transitions can be analyzed in terms of the shape of the energy surface, which gives the energy as a function of the angles determining the orientation of the magnetic moments. Minima on the energy surface correspond to stable or metastable magnetic states and can represent parallel, antiparallel or, more generally, non-collinear arrangements. A rate theory has been developed for systems with arbitrary number, N, of magnetic moments, to estimate the thermal stability of magnetic states and the mechanism for magnetic transitions based on a transition state theory approach. The minimum energy path on the 2N-dimensional energy surface is determined to identify the transition mechanism and estimate the activation energy barrier. A pre-exponential factor in the rate expression is obtained from the Landau–Lifshitz–Gilbert equation for spin dynamics. The velocity is zero at saddle points so it is particularly important in this context to realize that the transition state is a dividing surface with 2N − 1 degrees of freedom, not just a saddle point. An application of this rate theory to nanoscale Fe islands on W(110) has revealed how the transition mechanism and rate depend on island shape and size. Qualitative agreement is obtained with experimental measurements both for the activation energy and the pre-exponential factor. In particular, a distinct maximum is observed in the pre-exponential factor for islands where two possible transition mechanisms are competing: Uniform rotation and the formation of a temporary domain wall. The entropy of the transition state is enhanced for those islands making the pre-exponential factor more than an order of magnitude larger than for islands were only the uniform rotation is viable.

Keywords: Rate Theory; Spin Transitions; Magnetic Memory; Magnetic Nano-Islands; Potential Energy Surface

About the article

Received: 2013-02-21

Published Online: 2013-07-08

Published in Print: 2013-11-01


Citation Information: Zeitschrift für Physikalische Chemie, Volume 227, Issue 9-11, Pages 1543–1557, ISSN (Online) 2196-7156, ISSN (Print) 0942-9352, DOI: https://doi.org/10.1524/zpch.2013.0403.

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© 2013 by Walter de Gruyter Berlin Boston. This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. BY-NC-ND 4.0

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The Journal of Chemical Physics, 2017, Volume 147, Number 15, Page 152720
[2]
Harri Mökkönen, Tapio Ala-Nissila, and Hannes Jónsson
The Journal of Chemical Physics, 2016, Volume 145, Number 9, Page 094901
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Søren Smidstrup, Andreas Pedersen, Kurt Stokbro, and Hannes Jónsson
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