Berlin 2008 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 35: Phase Transitions I

MM 35.3: Vortrag

Donnerstag, 28. Februar 2008, 10:45–11:00, H 0107

Ferromagnetic shape memory alloy Mn₂NiGa: — •Guodong Liu and Claudia Felser — Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg - University, 55099 Mainz

The structure, martensitic transformation and magnetic properties of Mn_25+xNi_50−xGa₂₅ (x=0⋯25) alloys were detailedly investigated. It was found that these alloys favour the Hg₂CuTi-type structure instead of the conventional Cu₂MnAl-type structure. All the samples go through a martensitic transformation on cooling. The transformation temperatures (TM) of the samples with x>12.5 are different from the conventional electron concentration rule. The stoichiometric Mn₂NiGa exhibits a TM of around room temperature and a lattice distortion as large as 21.3% upon the martensitic transformation and has a quite high Curie temperature of 588 K. Excellent two-way shape memory behavior and magnetic-field-controlled effects were observed in Mn₂NiGa single crystals. The electronic structures of Mn₂NiGa were calculated by the first-principle method. The results show that Mn₂NiGa alloy is ferrimagnetic due to antiparallel but uncompensated magnetic moments of Mn atoms at different sublattices in austenite. Furthermore, is shown for off-stoichiometric samples that additional Mn atoms substituting Ni atoms in Ni₂MnGa have the same magnetic behavior as Mn in the Mn₂NiGa phase, which explains the dependence of the magnetization on the Mn composition. (Goudong Liu acknowledges the support by the Institute of Physics, Chinese Academy of Sciences in Beijing and the fellowship by the Humboldt Stiftung.)