Abstract
The geometrically frustrated double perovskite BaYMoO is characterized by quantum spins at the Mo sites of an undistorted fcc lattice. Previous low-temperature characterization revealed an absence of static long-range magnetic order and suggested a nonmagnetic spin-singlet ground state. We report unique time-of-flight and triple-axis neutron spectroscopy of BaYMoO that shows a 28 meV spin excitation with a bandwidth of 4 meV, which vanishes above 125 K. We identify this as the singlet-triplet excitation that arises out of a singlet ground state, and further identify a weaker continuum of magnetic states within the gap, reminiscent of spin-polaron states arising due to weak disorder.
- Received 20 May 2011
DOI:https://doi.org/10.1103/PhysRevB.84.100404
©2011 American Physical Society