Giant magnetic-field-induced strain in NiMnGa seven-layered martensitic phase

Giant magnetic-field-induced strain of about 9.5% was observed at ambient temperature in a magnetic field of less than 1 T in NiMnGa orthorhombic seven-layered martensitic phase. The strain proved to be caused by magnetic-field-controlled twin boundary motion. According to an analysis of x-ray diffraction data, the crystal structure of this phase is nearly orthorhombic, having lattice parameters $a=0.619 nm,$ $b=0.580 nm,$ and $c=0.553 nm$ (in cubic parent phase coordinates) at ambient temperature. Seven-layer shuffling-type modulation along the $(110)[11̄0]p$ system was recorded. The results of mechanical tests and magnetic anisotropy property measurements are also reported.