A free energy model for magneto-mechanically coupled NiMnGa single crystals

  • P. Morrison
  • S. SeeleckeEmail author
  • B. Krevet
  • M. Kohl


This paper presents a one-dimensional magneto-mechanical model for NiMnGa. Following a modeling approach developed by the authors for conventional shape memory behavior and ferroelectricity, a constitutive Helmholtz free energy landscape with strain and magnetization as order parameters is constructed for a representative meso-scale lattice element. The landscape includes three paraboloidal energy wells representing the two easy-axis and one hard-axis martensite variants distinguishable in the chosen coordinate system. The resulting stress- and magnetic-field-dependent Gibbs free energy expressions are then used within the theory of thermally activated processes to derive a series of phase-fraction evolution equations. The phase fractions subsequently determine the macroscopic strain and magnetization of a sample of NiMnGa by a standard averaging procedure. Results from the model are compared to experimental data and demonstrate the model's ability to reproduce constitutive behaviors of the material. Future work includes an extension to a full thermo-magneto-mechanical model accounting for the occurrence of austenite and inhomogeneity effects and configured to function within the tensile-stress regime.


Martensite Shape Memory Shape Memory Alloy European Physical Journal Special Topic Crystal Layer 
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Copyright information

© EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2008

Authors and Affiliations

  1. 1.Dept. of Mech. and Aerospace Engineering, North Carolina State UniversityRaleighUSA
  2. 2.Forschungszentrum Karlsruhe, Institute of Microstructure TechnologyKarlsruheGermany

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