SOFT MODES IN NI2MNGA SINGLE-CRYSTALS

We report on measurements of the thermal diffuse x-ray intensity from a single crystal of Ni2MnGa in the temperature range 180 to 250 K. The martensitic phase transition is clearly to be seen. It is accompanied by a strong soft-mode behaviour in the transverse acoustic phonon bra nch with q along the [110] direction and polarization along [110BAR] i n the high-temperature phase. A peak splitting and a super-structure c haracterize the low-temperature martensitic phase.