Investigate phonon excitations in the strong magnetoelastic and magnetoelectric TbPO4

TbPO4 exhibits one of the strongest magnetoelectric (ME) coupling among bulk materials. This effect is intimately related to a substantial magnetoelastic coupling, revealed by our preliminary work. The large magnetoelastic effect and structural deformations characterizing the compound play a key role in developing such a strong ME effect. Previous studies suggest that TbPO4 crystal structure can easily distort, giving rise to soft phonon modes behavior. Yet the phonon spectra of TbPO4 remain uninvestigated with neutron spectroscopy and modern DFT methods. Here, we propose to study the phonon spectra on MERLIN, with a special focus on the crossing point of phonon modes with crystal electric field levels. At these points, we expect to see the footprint of the very large magnetoelastic coupling. The result will contribute to understanding the mechanism behind both the magnetoelastic and magnetoelectric effects. We started a DFT calculation and the neutron data are essential to elucidate the phonons dispersion spectrum and deepen the DFT calculations.