Hybrid magnon-phonons in the paraelectric antiferromagnet EuTiO$_{3}$

Magnetic perovskite titanate EuTiO$_{3}$ has attracted a lot of attentions for its large spin-lattice coupling. It has a number of similarities with the well-studied quantum paraelectric SrTiO$_{3}$ but a much higher cubic-tetragonal lattice transition at 290 K and an extra magnetic order at 5.5 K. The large difference between EuTiO$_{3}$ and SrTiO$_{3}$ has been attributed to the magnetic ion Eu$^{2+}$, that couples with the structural properties. However the spin-lattice coupling mechanism has not been fully understood yet although many theoretical models have been proposed. We grew a large, high-quality isotopically-enriched EuTiO$_{3}$ crystal for neutron scattering.~ The crystal and magnetic structures were calibrated with neutron diffraction at HB-3A at HFIR at ORNL at temperatures from 1.5 K to 450 K. The spin waves and phonons were measured in the temperature range of 1.5-400 K with HB-3 at HFIR, CNCS and ARCS at SNS at ORNL. I will report our new discovery of interaction between the soft ferroelectric phonon mode and likely (para)magnon mode, that is responsible for a giant magnetoelectric coupling in EuTiO$_{3}$. The magnetic excitation and atomic displacements will be discussed.