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  • 1
    Electronic Resource
    Electronic Resource
    Universality in two-dimensional magnetic systems : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6096-6098 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-dimensional magnetic behavior in thin films and in layered magnets apparently falls into one of only two universality classes. The first is that of the 2D Ising model, characterized by a magnetization exponent β=1/8. The second, with β≈0.23, is observed in systems with planar spin symmetry. Recently it has been shown, using a modified renormalization group calculation, that β=0.23 is a property of a finite size XY model. Although there is no broken symmetry in this system, correlations below the Kosterlitz–Thouless transition temperature decay so slowly that a magnetization occurs in any realizable system, and β=0.23 is a result of two-dimensional fluctuations. By considering a large number of experimental situations we demonstrate that this rule is generally obeyed, and can be used as a test to identify two-dimensional behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353481
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetization of two-dimensional XY magnets with symmetry breaking fields: Relevance to ultrathin magnetic films (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4976-4976 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetization of ultrathin films shows a power law dependence on temperature with an exponent β that depends on the spin anisotropy. Experimentally it is found that films with easy-axis anisotropy show β=1/8, characteristic of the two-dimensional Ising model, while those with dominant easy-plane anisotropy show β=0.23. We recently discussed the finite size magnetization of the XY model and showed that this system has universal behavior which leads to the exponent β=0.23. A number of authors have therefore interpreted their results in terms of the finite size two-dimensional XY model. The success of these explanations implies that the four- and sixfold anisotropy fields present in real films are irrelevant in determining the critical behavior of the magnetization. In the sixfold case this observation agrees with theoretical expectations, while in the fourfold case the situation is unclear, as the renormalization group analysis of José et al. shows the fourfold field to be a marginally relevant variable which gives rise to nonuniversal exponents. This theoretical result, however, pertains to the thermodynamic limit and is not necessarily relevant to real finite systems. We investigate the effect of symmetry breaking fields on the magnetic behavior of idealized finite size XY models by means of Monte Carlo simulation. We find that the fourfold field is indeed irrelevant for the system sizes of interest, and may only become relevant for system sizes beyond the physical domain. We also confirm that the sixfold field is both qualitatively and quantitatively irrelevant, and notice a number of novel features connected with the behavior of finite size models which cannot be observed in the thermodynamic limit. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361859
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  • 3
    Electronic Resource
    Electronic Resource
    Can the universal jump be observed in two-dimensional XY magnets? : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5955-5957 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The universal jump in the spin-wave stiffness is a characteristic property of the Kosterlitz–Thouless–Berezinskii phase transition in an infinitely large 2D-XY magnet. It has recently been demonstrated [S. T. Bramwell and P. C. W. Holdsworth, J. Phys. Condens. Matt. 5, L53 (1993)] that finite-size rounding is much more important in two-dimensional than in three-dimensional systems. This is because the properties of the phase transition depend logarithmically, rather than algebraically, on the system size. Consequently, finite-size rounding will be dominant in any real, macroscopic 2D-XY magnet. How the rounded universal jump still exhibits observable universal properties is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355524
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  • 4
    Electronic Resource
    Electronic Resource
    Universality of rare fluctuations in turbulence and critical phenomena (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 396 (1998), S. 552-554 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A statistical treatment of three-dimensional turbulent flow continues to pose a challenge to theorists,. One suggestion invokes an analogy with equilibrium phase transitions. Here we approach this idea experimentally, presenting evidence of a strong analogy between the statistical behaviour of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/25083
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