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

TL;DR

This study investigates the nonlinear dielectric behavior of three triple-perovskite ruthenates at low temperatures, revealing complex spin-charge-lattice interactions and phase dynamics through higher-order susceptibility measurements.

Contribution

It provides the first detailed analysis of nonlinear dielectric susceptibilities in these ruthenates, uncovering complex relaxation phenomena and coupling effects not observable via linear responses.

Findings

Ba3CoRu2O9 shows frequency-dependent relaxation above 100K

Ba3BiRu2O9 exhibits multiple coexisting relaxation behaviors

Sr3CaRu2O9 demonstrates anomalies near magnetic transitions

Abstract

We report the nonlinear dielectric properties of three triple-perovskite ruthenates: Ba$_3$CoRu$_2$O$_9$, Ba$_3$BiRu$_2$O$_9$, and Sr$_3$CaRu$_2$O$_9$. These compounds exhibit notable correlations among their spin, charge, lattice, and polar degrees of freedom. Ba$_3$CoRu$_2$O$_9$ displays a pronounced frequency-dependent relaxation in $\chi_{2,3}$ just above the magnetoelastic transition, occurring around 100K, followed by an abrupt loss of polarization within the ordered phase. In Ba$_3$BiRu$_2$O$_9$, we encounter the possibility of multiple coexisting relaxation behaviors, indicating a complex phase strongly influenced by the spin-gap opening at 175K. Lastly, Sr$_3$CaRu$_2$O$_9$ displays anomalies with strong dispersion effects close to its magnetic transitions, pointing to 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.