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Keywords:

  • magneto-elastic coupling;
  • Ni-Mn-Ga;
  • premartensite;
  • tweed microstructure

Magnetic, magneto-elastic and elastic measurements were used to characterize the thermal evolution of the premartensite phase of Ni2 MnGa. The premartensitic transition is shown to correspond to a sharp maximum of magnetostriction and a pronounced minimum of the (110) inline image shear stiffness (the inline image elastic coefficient); no additional softening of the inline image coefficient prior to the martensitic transformation was observed. In contrast, a significant softening of the (100) inline image stiffness (the inline image elastic coefficient) was observed in the vicinity of the martensitic transition, while this coefficient is fully unaffected by the premartensitic transition. A simple two-dimensional model of the tweed is presented to explain this mutual independence between the inline image and inline image shears and the effect of tweed formation on both of them.