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Title: Modified Heisenberg model for the zig-zag structure in multiferroic RMn{sub 2}O{sub 5}

The class of RMn{sub 2}O{sub 5} (R = Ho, Tb, Y, Eu) compounds offers multiferroic properties where the refined magnetic zig-zag order breaks the inversion symmetry. Varying the temperature, the system undergoes a magnetic and a subsequent ferroelectric phase transition where the ferroelectricity is magnetically induced. We propose a modified anisotropic Heisenberg model that can be used as a tractable analytical model studying the properties of those antiferromagnetic zig-zag spin chains. Based on a finite temperature Green's function method, it is shown that the polarization is induced solely by different exchange couplings of the two different Mn{sup 4+} and Mn{sup 3+} magnetic ions. We calculate the excitation energy of the spin system for finite temperatures, which for its part determines the temperature dependent magnetization and polarization. The ferroelectric phase transition is manifested as a kink in the excitation energy. The variation of the polarization by an external magnetic field depends strongly on the direction of that field. Whereas, the polarization in b-direction increases with an external magnetic field as well in b-direction it can be switched for strong fields in a-direction. The results based on that modified Heisenberg model are in qualitative agreement with experimental data.
Authors:
 [1] ;  [2] ;  [3]
  1. Department of Physics, University of Konstanz, D-78457 Konstanz (Germany)
  2. Department of Physics, University of Sofia, 1164 Sofia (Bulgaria)
  3. Institute of Physics, Martin-Luther-University Halle-Wittenberg, D-06099 Halle (Germany)
Publication Date:
OSTI Identifier:
22494792
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANISOTROPY; ANTIFERROMAGNETISM; EUROPIUM COMPOUNDS; EXCITATION; EXPERIMENTAL DATA; FERROELECTRIC MATERIALS; HEISENBERG MODEL; HOLMIUM COMPOUNDS; MAGNETIC FIELDS; MAGNETIZATION; MANGANESE IONS; PHASE TRANSFORMATIONS; POLARIZATION; SPIN; SYMMETRY; TEMPERATURE DEPENDENCE; TERBIUM COMPOUNDS; YTTRIUM COMPOUNDS