Spin-gap opening accompanied by a strong magnetoelastic response in the S=1 magnetic dimer system Ba3BiRu2O9

TL;DR

This study reveals a magnetoelastic-driven transition in Ba3BiRu2O9, where magnetic and structural dimerization occur simultaneously, leading to a spin-gapped state without long-range magnetic order.

Contribution

It demonstrates the strong coupling between magnetic and structural properties in Ba3BiRu2O9 and characterizes the transition as a magnetoelastic-driven dimerization.

Findings

First-order transition at 176 K involves structural and magnetic dimerization.

Above T*, the system exhibits S=1 magnetic dimers with strong exchange interactions.

Below T*, a spin gap of approximately 220 K develops without long-range magnetic order.

Abstract

Neutron diffraction, magnetization, resistivity, and heat capacity measurements on the 6H-perovskite Ba3BiRu2O9 reveal simultaneous magnetic and structural dimerization driven by strong magnetoelastic coupling. An isostructural but strongly displacive first-order transition on cooling through T*=176 K is associated with a change in the nature of direct Ru-Ru bonds within Ru2O9 face-sharing octahedra. Above T*, Ba3BiRu2O9 is an S=1 magnetic dimer system with intradimer exchange interactions J0/kB=320 K and interdimer exchange interactions J'/kB=-160 K. Below T*, a spin-gapped state emerges with \Delta\approx220 K. Ab initio calculations confirm antiferromagnetic exchange within dimers, but the transition is not accompanied by long range-magnetic order.