6% magnetic-field-induced strain by twin-boundary motion in ferromagnetic Ni-Mn-Ga

Field-induced strains of 6% are reported in ferromagnetic Ni-Mn-Ga martensi tes at room temperature. The strains are the result of twin boundary motion driven largely by the Zeeman energy difference across the twin boundary. T he strain measured parallel to the applied magnetic field is negative in th e sample/field geometry used here. The strain saturates in fields of order 400 kA/m and is blocked by a compressive stress of order 2 MPa applied orth ogonal to the magnetic field. The strain versus field curves exhibit apprec iable hysteresis associated with the motion of the twin boundaries. A simpl e model accounts quantitatively for the dependence of strain on magnetic fi eld and external stress using as input parameters only measured quantities. (C) 2000 American Institute of Physics. [S0003-6951(00)00832-9].