Abstract
TbBaFe2O5+δ (TBFO) is a mixed valence compound with an antiferromagnetic order (TN=450K) that changes along with the crystal structure and conductivity upon cooling below a Verwey-like transition (TV=280K). This type of double-cell-layered perovskite is useful to study putative charge ordering in fractional valence systems because the crystal structure develops unique sites for the different valence states. While the evolution of the static magnetic structure in the different charge ordered states of TBFO is known, in this study we investigate the effect of charge ordering on the magnetic interactions. Dispersive magnetic excitations measured using single crystal inelastic neutron scattering experiments at T=4K<TV and T=320K>TV are modeled with linear-spin-wave theory to extract anisotropy and superexchange parameters. Below TV, we observe a sizable magnon gap due to an easy-axis magnetic anisotropy that closes above TV due to the evolution of easy-plane anisotropy. The magnetic interactions are found to be highly three-dimensional and change across TV. Above TV, where the conductivity is greater, a damping term is required to model the spin waves that suggests a coupling to valence fluctuations.
| Original language | English |
|---|---|
| Article number | 064418 |
| Journal | Physical Review B |
| Volume | 101 |
| Issue number | 6 |
| DOIs | |
| State | Published - Feb 1 2020 |
Funding
D.M.P., S.E.H., W.T., G.E.G., and A.I.K. are supported through the Scientific User Facilities Division of the Department of Energy (DOE) Office of Science, sponsored by the Basic Energy Science (BES) Program, DOE Office of Science. Work at the Ames Laboratory was supported by the DOE, Office of BES, Division of Materials Sciences and Engineering. Ames Laboratory is operated for the DOE by Iowa State University under Contract No. DE-AC02-07CH11358. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. We acknowledge Lisa DeBeer-Schmitt for help setting up the experiment, and Matthieu Doucet for conversations about model fitness. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).