  A quantitative model describing large magnetostrain effect observed in
several ferromagnetic shape memory alloys such as Ni2MnGa is briefly
reported.The paper contains an exact thermodynamic consideration of the
mechanical and magnetic properties for a similar type materials. As a result,
the basic mechanical state equation including magnetic field effect is directly
derived from a general Poisson's rule. It is shown that the magnetic field
induced deformation effect is directly connected with the strain dependence of
magnetization. A simple model of magnetization and its dependence on the strain
is considered and applied to explain the results of experimental study of large
magnetostrain effects in Ni2MnGa.
