title: Valence bond glass on an fcc lattice in the double Perovskite Ba2YMoO6.
abstract: We report on the unconventional magnetism in the cubic B-site ordered double perovskite Ba2YMoO6, using ac and dc magnetic susceptibility, heat capacity and muon spin rotation. No magnetic order is observed down to 2 K while the Weiss temperature is approximately -160 K. This is ascribed to the geometric frustration in the lattice of edge-sharing tetrahedra with orbitally degenerate Mo5+ s=1/2 spins. Our experimental results point to a gradual freezing of the spins into a disordered pattern of spin singlets, quenching the orbital degeneracy while leaving the global cubic symmetry unaffected, and providing a rare example of a valence bond glass.
authors.affiliation: School of Physics and Astronomy, E. C. Stoner Laboratory, University of Leeds, Leeds, LS2 9JT, United Kingdom. m.a.devries@physics.org
authors.forename: M A
authors.initials: MA
authors.lastname: de Vries
authors.forename: A C
authors.initials: AC
authors.lastname: McLaughlin
authors.forename: J-W G
authors.initials: JW
authors.lastname: Bos