Browsing by Author "Shapiro, SM"

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    Observation of phasons in the magnetic shape memory alloy Ni2MnGa
    (IOP Sciences, 2007-03) Shapiro, SM; Vorderwisch, P; Habicht, K; Hradil, K; Schneider, H
    An inelastic neutron scattering study of the lattice dynamics of the martensite phase of the ferromagnetic shape memory alloy, Ni2MnGa, reveals the presence of well-defined phasons associated with the charge density wave (CDW) resulting from Fermi surface (FS) nesting. The velocity and the temperature dependence of the phason are measured as well as the anomalous [110]-TA(2) phonon. © 2007, EPLA
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    Phason mode in the incommensurate martensitic phase of Ni2MnGa - observed by neutron spectroscopy
    (Australian Institute of Physics, 2006-12-04) Vorderwisch, P; Shapiro, SM; Habicht, K; Hradil, K; Schneider, H
    The ferromagnetic shape-memory alloy Ni2MnGa, of technological interest as a magnetically driven actuator, undergoes a martensitic transformation from a cubic austenite to a tetragonally distorted martensite structure. Previous inelastic neutron scattering experiments, performed in the martensite phase, show an anomaly in the phonon dispersion for the [110] transverse acoustic branch TA2 [1]. This anomaly is identified (in ab-initio calculations through examination of Fermi-surface nesting and electron-phonon coupling) as a Kohn anomaly [2] and occurs at a wave vector incommensurate with the underlying lattice. Elastic neutron scattering reveals a modulation of the martensite phase with this incommensurate wave vector [1]. In very recent inelastic experiments, performed with cold- and thermal-neutron triple-axis-spectrometers, in addition to the known acoustic branch a new dispersive branch was found, showing all characteristics of a phason mode. In our interpretation, the new mode is caused by a charge-density-wave in the incommensurately distorted lattice. Inelastic neutron scattering is the only technique able to unambiguously detect a phason branch - and successful examples are rare. [1] P. Vorderwisch and S.M. Shapiro, submitted [2] C. Bungaro et al., Phys. Rev. B 68 (2003) 134104