Lattice dynamics and phonon softening in Ni-Mn-Al Heusler alloys
  Inelastic and elastic neutron scattering have been used to study a single crystal of the Ni$_{54}$Mn$_{23}$Al$_{23}$ Heusler alloy over a broad temperature range. The paper reports the first experimental determination of the low-lying phonon dispersion curves for this alloy system. We find that the frequencies of the TA$_2$ modes are relatively low. This branch exhibits an anomaly (dip) at a wave number $\xi_{0} ={1/3}\approx 0.33$, which softens with decreasing temperature. Associated with this anomalous dip at $\xi_{0}$, an elastic central peak scattering is also present. We have also observed satellites due to the magnetic ordering. 
Xavier Moya, Llu\'is Ma\~nosa, Antoni Planes, Thorsten Krenke, Mehmet   Acet, V. O. Garlea, T. A. Lograsso, D. L. Schlagel, ...