Exploring low-temperature dynamics in triple perovskite ruthenates using nonlinear dielectric susceptibility measurements

Abstract

We report the nonlinear dielectric properties of three triple-perovskite ruthenates: Ba3CoRu2O9⁠, Ba3BiRu2O9⁠, and Sr3CaRu2O9⁠. These compounds exhibit notable correlations among their spin, charge, lattice, and polar degrees of freedom. Ba3CoRu2O9 displays a pronounced frequency-dependent relaxation in �2,3 just above the magnetoelastic transition, occurring around 100 K, followed by an abrupt loss of polarization within the ordered phase. In Ba3BiRu2O9⁠, we encounter the possibility of multiple coexisting relaxation behaviors, indicating a complex phase strongly influenced by the spin-gap opening at 175 K. Lastly, Sr3CaRu2O9 displays anomalies with strong dispersion effects close to its magnetic transitions, indicating a robust coupling between magnetic and dipolar orders in the system. These measurements highlight the significance of higher-order (hyper-)susceptibilities in providing profound insight into the dynamics of a system, offering information otherwise inaccessible through the linear polarization response alone.