The European Physical Journal B

, Volume 80, Issue 3, pp 331–336 | Cite as

Spin-spin correlations in ferromagnetic nanosystems

  • E. Y. Vedmedenko
  • N. Mikuszeit
  • T. Stapelfeldt
  • R. Wieser
  • M. Potthoff
  • A. I. Lichtenstein
  • R. Wiesendanger
Article

Abstract.

Using exact diagonalization, Monte-Carlo, and mean-field techniques, characteristic temperature scales for ferromagnetic order are discussed for the Ising and the classical anisotropic Heisenberg model on finite lattices in one and two dimensions. The interplay between nearest-neighbor exchange, anisotropy and the presence of surfaces leads, as a function of temperature, to a complex behavior of the distance-dependent spin-spin correlation function, which is very different from what is commonly expected. A finite experimental observation time is considered in addition, which is simulated within the Monte-Carlo approach by an incomplete statistical average. We find strong surface effects for small nanoparticles, which cannot be explained within a simple Landau or mean-field concept and which give rise to characteristic trends of the spin-correlation function in different temperature regimes. Unambiguous definitions of crossover temperatures for finite systems and an effective method to estimate the critical temperature of corresponding infinite systems are given.

Keywords

Correlation Function Curie Temperature System Size Exact Diagonalization Crossover Temperature 

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Copyright information

© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  • E. Y. Vedmedenko
    • 1
  • N. Mikuszeit
    • 2
  • T. Stapelfeldt
    • 1
  • R. Wieser
    • 1
  • M. Potthoff
    • 3
  • A. I. Lichtenstein
    • 3
  • R. Wiesendanger
    • 1
  1. 1.University of Hamburg, Institute for Applied PhysicsHamburgGermany
  2. 2.Instituto Madrileño de Estudios Avanzados en Nanociencia, IMDEA-Nanociencia, Campus Universidad Autónoma de MadridMadridSpain
  3. 3.University of Hamburg, I. Institute for Theoretical PhysicsHamburgGermany

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