Magnetic Order and Multipoles in the 5d2 Rhenium Double Perovskite Ba2 YRe O6

Ba2YReO6 is a double perovskite material where the Re5+ (d2) ions occupy a frustrated face-centered cubic lattice. Despite strong antiferromagnetic interactions between the Re ions, as indicated by a large negative Weiss constant θ=-616 K, spin freezing in Ba2YReO6 only occurs at 45 K. Since no long-range order of magnetic dipoles has previously been found in either muon spin rotation or neutron diffraction experiments below this temperature, it has been assumed that the low-temperature state is a spin glass. In stark contrast with these findings, we here show that Ba2YReO6 does in fact order with a strongly reduced dipole moment μ0=0.29-0.42μB via a polarized neutron diffraction experiment on a powder sample. Using the symmetries of the two likeliest magnetic structures and the properties of the 5d2 configuration in the presence of strong spin-orbit coupling and strong crystal fields, we use a recently derived single-ion wave function for Re5+ to predict a large quadrupolar moment based on the experimental μo. © 2021 American Physical Society.We thank A. A. Aczel, D. D. Khalyavin, and S. W. Lovesey for useful discussions, and S. W. Lovesey for several useful comments on the paper. J.E.G. thanks the Natural Sciences and Engineering Research Council (NSERC) of Canada for support through the Discovery Grant Program