Muon Spin Relaxation Study of the Complex Magnetic Ground States of a Ruthenate Dimer System

The compound Ba3HoRu2O9 is only Ru(4d)-based compound which exhibits spin-driven ferroelectricity. The magnetic ground state is quite intriguing. The compound magnetically orders at 50 K (TN1), where both the Ho and Ru moments initiate their ordering, followed by another magnetic phase transition at 10 K (TN2). The spin-driven ferroelectric polarisation is demonstrated below TN2 due to strong Ru(4d)-Ho(4f) coupling. We observe frequency dependence behaviour in dielectric measurements (10-500 kHz), whereas, such frequency dependence behaviour is absent in ac magnetic susceptibility (1Hz-1kHz). Being a spin-driven ferroelectric system, the spin and dipole moments are intertwined. Therefore, dipolar relaxation is expected to be linked to spin relaxation. µSR is an ideal tool to investigate such spin-relaxation phenomena, particularly considering the response of magnetic domains to higher frequency regimes (> 1 kHz). Additionally, our research aims to explore the relatively weak cooperative magnetic ordering at TN1 (50 K) and the nature of short-range ordering (SRO) far above TN1. Furthermore, longitudinal-field (LF) µSR experiments will provide valuable insights into the magnitude of the internal magnetic field at the specific muon-stopping site within the compound. The capabilities of the EMU (or HIFI) instrument are ideal for conducting these experiments, providing valuable insights into the compound's magnetic properties and magnetic (thus, magnetoelectric) domain dynamics.