Affiliations: [a] Faculty of Science & Technology, Ryukoku
University, Seta, Otsu 520-2194, Japan | [b] IMR, Tohoku University, Aoba-ku, Sendai 980-8577,
Japan | [c] Japan Atomic Energy Research Institute, Tokai, Ibaraki
319-1195, Japan | [d] Faculty of Science , Nara Women's University, Nara
630-8506, Japan | [e] Materials Science & Technology, University of
Washington, Box 35210, WA 98196, USA
Abstract: We have made the Heusler-type Ni_2MnGa-based
alloys, Ni_{2.18}Mn_{0.82}Ga,
Ni_{2.19}Mn_{0.81}Ga and
Ni_2Mn_{0.92}Ga_{1.08},
which have the martensitic transformation temperature coincident with the Curie
temperature. The powder neutron diffraction measurements of these alloys were
performed. The Rietveld analysis of the diffraction patterns showed that at
least two crystal structures coexist in each martensitic phase. For
Ni_{2.18}Mn_{0.82}Ga and
Ni_{2.19}Mn_{0.81}Ga, the main structure
is a monoclinic one with a six-layers shuffling and a small amount of
orthorhombic structure distorted from the cubic Heusler one is included. For
Ni_2Mn_{0.92}Ga_{1.08},
the main structure is tetragonal whereas a small amount of other structures
seem to be included. The neutron diffraction of
Ni_{2.19}Mn_{0.81}Ga under magnetic field
up to 5 T at the coincident transformation temperature of 350 K shows that the
magnetic field causes the phase transformation from cubic phase to martensitic
one. The result suggests the possibility of controlling the shape memory effect
originating from the thermoelastic martensitic transformation, by applying the
external magnetic field instead of changing the temperature.
