Inelastic neutron scattering study of molecular multiferroic (ND₄)₂[FeCl₅(D₂O)]

(ND₄)₂[FeCl₅(D₂O)] was recently discovered to exhibit magnetically induced multiferroicity. At zero field, the system first undergoes a magnetic long-range order transition to an incommensurate (IC) collinear sinusoidal spin state at T_N=7.3 K, followed by a second transition to an IC cycloidal spin state at T_FE=6.8K accompanied by spontaneous ferroelectric polarization. Applying modest magnetic field along a, or c-axis induces transitions to distinct magnetic and ferroelectric phases. Here we report preliminary inelastic neutron scattering results that reveal the spin dynamic in this molecular multiferroic material.