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Elasticity and magnetism of Ni2 MnGa premartensitic tweed



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) math formula shear stiffness (the math formula elastic coefficient); no additional softening of the math formula coefficient prior to the martensitic transformation was observed. In contrast, a significant softening of the (100) math formula stiffness (the math formula 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 math formula and math formula shears and the effect of tweed formation on both of them.