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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 χ2,3 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.
Chakravarty et al. (Tue,) studied this question.