Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 17: Magnetic Shape Memory Alloys

MA 17.3: Talk

Wednesday, March 28, 2007, 15:45–16:00, H10

Lattice dynamics in austenitic and martensitic phase of Ni₂MnGa from inelastic neutron scattering — •Tarik Mehaddene¹, Jürgen Neuhaus², Winfried Petry^2,1, Klaudia Hradil^3,2, and Peter Link² — ¹Physik-Department E13, Technische Universität München, 85748 Garching — ²Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), 85748 Garching — ³Institut für Physikalische Chemie, Universität Göttingen, 37077 Göttingen

We report on the investigation of the normal modes of vibration in the martensitic and austenitic phase of Ni₂MnGa by inelastic neutron scattering. Phonon dispersions of both acoustic and optical phonons in a Ni₄₉Mn₃₁Ga₂₀ single crystal have been measured on the three-axis spectrometer PUMA (Forschungsneutronenquelle Heinz Maier-Leibnitz, Garching). The sample undergoes a martensitic transformation at M_s=350 K and orders ferromagnetically below T_c=385 K. We focus on the optical phonons and their temperature dependence, which, to our knowldge, has not been reported yet despite of the intensive previous works on Ni₂MnGa. Acoustic phonons of an orthorhombic 7-layered martensitic variant of the same sample have been measured on both thermal (PUMA) and cold (PANDA) three-axis spectrometers. The measurements revealed low-lying TA₂[ξξ 0] phonon frequencies with a Brillouin zone boundary frequency of 2.5 THz.