Finite energy solitons in highly anisotropic two dimensional ferromagnets

B. A. Ivanov, A. Yu. Merkulov, V. A. Stephanovich, and C. E. Zaspel
Phys. Rev. B 74, 224422 – Published 18 December 2006

Abstract

We study the solitons, both topological and nontopological, stabilized by spin precession in a classical two-dimensional lattice model of Heisenberg ferromagnets (FM) with easy-axial anisotropy. These solitons can be regarded as bound states of large number N of magnons, their properties are treated both analytically using a continuous model and numerically for a discrete set of the spins on a square lattice. Both exchange anisotropy with constant κ and single-ion anisotropy with constant K are taken into account. In continuum approximation, both terms give additive contributions to the effective anisotropy constant Keff=K+2κ. Beyond this approximation, the properties of solitons depend on the microscopic origin of anisotropy. Solitons can be conveniently classified in the (Keff,N) plane. We have shown that the stable solitons exist for N higher than some critical value Ncr. At N>Ncr and for Keff<0.3J, J is exchange constant, the solitons in FM with any type of anisotropy could be described fairly well by continuum model. The continuum description fails at Keff(0.30.4)J for exchange anisotropy, but still valid for FM’s with a single-ion anisotropy up to Keff0.6J. For higher values of anisotropy, the continuous approach is no more valid and the above discrete model should be used. For Keff>0.6J, in the entire range of N values, we found some fundamentally new soliton features absent in continuum models. Namely, the soliton energy E(N) becomes non-monotonic with the minima at some “magic numbers” of N. In this case, the soliton frequency ω(N)=dE(N)dN have quite irregular behavior, with step-like jumps and negative values of ω for some N regions. In these regions, the static soliton textures, stabilized by the lattice effects, are present.

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  • Received 10 June 2006

DOI:https://doi.org/10.1103/PhysRevB.74.224422

©2006 American Physical Society

Authors & Affiliations

B. A. Ivanov*

  • Institute of Magnetism, 04071 Kiev, Ukraine and National Taras Shevchenko, University of Kiev, 03127 Kiev, Ukraine

A. Yu. Merkulov

  • FOM Institute for Atom and Molecular Physics, Macromolecular Ion Physics Group, Kruislaan 407 1098 SJ Amsterdam, The Netherlands

V. A. Stephanovich

  • Institute of Mathematics and Informatics, Opole University, 45-052, Opole, Poland

C. E. Zaspel

  • University of Montana-Western, Dillon, Montana 59725, USA

  • *Electronic address: bivanov@i.com.ua
  • http://cs.uni.opole.pl/̃stef;Electronic address: stef@math.uni.opole.pl

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Issue

Vol. 74, Iss. 22 — 1 December 2006

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