10% magnetic-field-induced strain in Ni-Mn-Ga seven-layered martensite

Magnetic-field-induced strain of approximately 10% is reported in Ni48.8Mn29.7Ga21.5 alloy at ambient temperature in a magnetic field of the order of I T. It was confirmed by different experimental methods that the strain is contributed by twin boundary motion. The crystal structure of thermally-induced martensitic phase in this alloy was found to be close to orthorhombic one in temperature range from 245 K to 333 K. The lattice parameters are a=0.619 nm, b=0.580 nm, c=0.553 nm (relating to the cubic parent phase coordinates) at ambient temperature. Detailed x-ray study revealed seven-layer modulation along the (110) [1(1) over bar 0](p) system. The results of mechanical tests and magnetic anisotropy property measurements are also reported. The necessary conditions for the observation of a giant magnetic field-induced strain in non-stoichiometric Ni2MnGa alloys based on the new experimental data are discussed.