Crystal-field excitations and spin-phonon interactions inDyNi2B2C: Raman scattering study

Abstract

We report polarized Raman results of magnetic superconductor ${\text{DyNi}}_{2}{\text{B}}_{2}\text{C}$ $({T}_{c}=6.2\text{ }\text{K},\text{ }{T}_{N}=10.3\text{ }\text{K})$ to explore crystal-field (CF) excitations and spin-phonon interactions. In addition to the $\text{Ni-}{B}_{1g}$ phonon mode at $199\text{ }{\text{cm}}^{\ensuremath{-}1}$, we observed additional Raman modes at 124, 151, and $221\text{ }{\text{cm}}^{\ensuremath{-}1}$. By careful analysis of the temperature evolution of these modes, we attribute the $124\text{ }{\text{cm}}^{\ensuremath{-}1}$ excitation to a CF transition. The 151 and $221\text{ }{\text{cm}}^{\ensuremath{-}1}$ modes correspond to zone-folded phonons because they are completely quenched for $T>{T}_{N}$. With increasing temperature across ${T}_{N}$, the $124\text{ }{\text{cm}}^{\ensuremath{-}1}$ excitation diminishes rapidly in intensity and, interestingly, an additional mode appears at $119\text{ }{\text{cm}}^{\ensuremath{-}1}$. This excitation grows in intensity with increasing temperature toward 50 K and gradually decreases with increasing temperature further. We attribute the $119\text{ }{\text{cm}}^{\ensuremath{-}1}$ excitation to an excited CF transition from a low-lying CF level at $5\text{ }{\text{cm}}^{\ensuremath{-}1}$ to the higher CF level at $124\text{ }{\text{cm}}^{\ensuremath{-}1}$. Anomalous temperature-dependent behavior of the $\text{Ni-}{B}_{1g}$ phonon mode was observed in peak energy and in spectral width, i.e., both the phonon energy and the linewidth are enhanced in the vicinity of ${T}_{N}$, suggesting the presence of strong spin-phonon interactions near the antiferromagnetic ordering temperature in ${\text{DyNi}}_{2}{\text{B}}_{2}\text{C}$.