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

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 Δ≈220 K. Ab initio calculations confirm antiferromagnetic exchange within dimers, but the transition is not accompanied by long-range magnetic order. ©2011 American Physical Society