Giant magnetoelasticity at a spin gap transition in the 5d oxide Ba3Bilr2O9
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Date
2013-12-03
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Australian Institute of Nuclear Science and Engineering
Abstract
The 4d and 5d transition metals have much more diffuse valence orbitals than their 3rd (first-row) transition metals. Quantum cooperative phenomena that arise due to changes in the way these orbitals overlap and interact, such as magnetoelasticity, are therefore relatively rare in 4d and 5d compounds. However, we recently discovered a 6H-perovskite Ba_3Bilr_2O_9, containing 5d lr"4"+ (S = 1/2) dimerised into isolated face-sharing lr_2O_9 bi-octahedra, which exhibits a giant magnetoelastic effect - the largest of any known 5d compound - upon the opening a spin-gap at T* = 74 K. The first-order transition observed by neutron powder diffraction is characterised by a remarkable 4% increase in Ir-Ir distance and 1% negative thermal volume expansion. The transition is driven by a dramatic change in the interactions among Ir 5d orbitals, and represents a crossover between two very different, competing, ground states: one that optimises direct lr-lr bonding (at high temperature); and one that optimises lr-O-lr magnetic superexchange (at low temperature).
Description
Hard copy held in ANSTO Library at DDC no. 539.758/15
Keywords
Dimerization, Thermal expansion, Transition elements, Neutron diffraction, Spin, Perovskite, Temperature dependence, Magnetic fields, Electronic structure, Electrical properties
Citation
Ling, C. D., Miiller, W., Kennedy, B. J., & Avdeev, M. (2013). Giant magnetoelasticity at a spin gap transition in the 5d oxide Ba3Bilr2O9. Paper presented at 11th AINSE-ANBUG Neutron Scattering Symposium AANSS 2013 Sydney, NSW, Australia, 2-3 December.