Crystal structure of martensite and intermediate phases in NiMnGa studied by neutron diffraction

Kushida, Hiroaki*; Fukuda, Kodai*; Terai, Tomoyuki*; Fukuda, Takashi*; Kakeshita, Tomoyuki*; Oba, Takuya*; Osakabe, Toyotaka  ; Kakurai, Kazuhisa; Kato, Kenichi*

We have investigated crystal structures of martensite and intermediate phases in stoichiometric NiMnGa. The neutron diffraction profile of the martensite phase measured at = 4.2 K exhibits four satellites between [2 0 0] and [0 2 0] refrections at incommensurate positions of [ 2 - 0] with = 0.428, 0.863, 1.136 and 1.572. The profile of the intermediate phase measured at = 210 K exhibits two satellites between [2 0 0] and [0 2 0] refrections at incommensurate positions of [ 2 - 0] with = 0.343 and 1.657. Although each satellite of the martensite phase moves toward its nearest fundamental refrection as temperature increases, that of the intermediate phase does not move significantly. On the contrary, the intensity of each satellite decreases significantly in the intermediate phase as temperature increases while not in the martensite phase. A synchrotron X-ray diffraction and a Rietveld analysis of the result reveal that, for both the phases, the displacement of atoms from the parent phase are represented by a sine wave whose propagation vector is parallel to [1 1 0].