Time-dependent evolution of martensitic structure caused by magnetic field in Ni2MnGa magnetic shape memory alloy

Changes in the martensite structure, magnetically controlled strain under applied magnetic field in the Ni2MnGa alloy are studied in-situ as a function of time at constant values of temperature and field. The measurements were performed under applied magnetic field and after magnetic field is taken out (after-effect). It is found that the change in the martensitic structure and the corresponding strain occur during exposures under magnetic field. After-effect is also observed when magnetic field is taken out. The direction of magnetic field is shown to strongly affect the time dependence of the structure and field-induced strain. The data of X-Ray diffraction, optical microscopy and measurements of strain support this conclusion.