Phonon anomaly, central peak, and microstructures in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>MnGa

Inelastic neutron scattering and transmission electron microscopy have been used to study a single crystal of the ${\mathrm{Ni}}_{2}$ MnGa shape-memory ferromagnetic Heusler alloy in a wide temperature range above the martensitic phase transformation at ${\mathit{T}}_{\mathit{M}}$=220 K. Significant, though incomplete, softening in the [\ensuremath{\zeta}\ensuremath{\zeta}0] ${\mathrm{TA}}_{2}$ phonon branch has been observed at a wave vector ${\mathrm{\ensuremath{\zeta}}}_{0}$\ensuremath{\approxeq}0.33. The anomaly in the dispersion curve is shown to persist at high temperature, even above the Curie point. A temperature-dependent peak in the elastic diffuse scattering is also present at the same wave vector ${\mathrm{\ensuremath{\zeta}}}_{0}$, which develops into a Bragg peak representative of an intermediate phase between the high-temperature Heusler and the low-temperature martensitic structures.