Abstract
The pressure dependence of the TA1[110] phonon frequencies in ordered Fe3Pt was studied by inelastic neutron scattering up to 7 GPa. Very large frequency shifts (∼ 50%) were observed in this pressure range. We found that the mode Grüneisen parameters remain very large (∼ 8) for pressures exceeding the critical pressure of about 3 GPa, which drives ordered Fe3Pt from a high-spin to a low-spin state. This indicates that the unusually large Grüneisen parameters are probably not a magnetoelastic effect, but rather have to be associated with the martensitic instability.