Study of crystal-field excitations and Raman active phonons in o-DyMnO3

In DyMnO3 orthorhombic single crystals, the weak Raman active phonon softening below T=100 K is correlated with the study of infrared active Dy3+ CF excitations as a function of temperature and under applied magnetic field. We detect five H13/2 CF transitions that we predict with appropriate CF Hamiltonian and we confirm that the magnetic easy axis lies in the ab plane. While the CF energy level shifts below T=100 K reflect different displacements of the oxygen ions that contribute to the phonon softening, lifting of the ground state Kramers doublet degeneracy (∼30 cm−1) is observed below TN=39 K due to the anisotropic Mn3+−Dy3+ interaction, which could be responsible for the stability of the bc-cycloid ferroelectric phase.

Research highlights
► Origin of Raman active phonon softening in the multiferroic o-DyMnO3.
► A crystal-field study under magnetic field of Dy3+ in o-DyMnO3.
► Location of the magnetic easy axis in o-DyMnO3.
► Lifting of Kramers doublet degeneracy in o-DyMnO3.