Experimental observation and computational study of the spin-gap excitation in Ba3BiRu2O9

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American Physical Society
Ba3BiRu2O9 is a 6H-type perovskite compound containing face-sharing octahedral M2O9 (M=Ir, Ru) dimers, which are magnetically frustrated at low temperatures. On cooling through T∗=176 K, it undergoes a pronounced magnetostructural transition, which is not accompanied by any change in space group symmetry, long-range magnetic ordering, or charge ordering. Here, we report the first direct evidence from inelastic neutron scattering that this transition is due to an opening of a gap in the excitation spectra of dimers of low-spin Ru4+ (S=1) ions. X-ray absorption spectroscopy reveals a change in Ru-Ru orbital overlap at T∗, linking the emergence of this spin-gap excitation to the magnetostructural transition. Ab initio calculations point to a geometrically frustrated magnetic ground state due to antiferromagnetic interdimer exchange on a triangular Ru2O9 dimer lattice. X-ray total-scattering data rule out long-range magnetic ordering at low temperatures, consistent with this geometrically frustrated model. ©2016 American Physical Society
Neutron diffraction, Absorption spectroscopy, X-ray diffraction, Antiferromagnetic materials, Temperature range 0065-0273 K, Inelastic scattering
Ling, C. D., Huang, Z., Kennedy, B. J., Rols, S., Johnson, M. R., Zbiri, M., Kimber, S. A. J, Hudspeth, J., Adroja, D. T., Rule, K. C., Avdeev, M., & Blanchard, P. E. R. (2016). Experimental observation and computational study of the spin-gap excitation in Ba 3 BiRu2O9. Physical Review B, 94(17), 174401. doi:10.1103/PhysRevB.94.174401