Diffraction by multipoles in a 5d2 rhenium double perovskite

TL;DR

This paper models the multipolar magnetic order in a 5d2 rhenium double perovskite, explaining experimental diffraction data through a symmetry-respecting wavefunction that predicts significant multipole moments.

Contribution

It introduces a theoretical wavefunction model incorporating crystal field, Coulomb, and spin-orbit effects to interpret neutron and x-ray diffraction data in the material.

Findings

Predicted multipole moments up to hexadecapole

Identified dominant charge-like quadrupole moment

Reproduced diffraction patterns consistent with experiments

Abstract

A recent polarized neutron diffraction experiment on the 5d2 rhenium double perovskite Ba2YReO6 held at a low temperature uncovered weak magnetic diffraction peaks. Data analysis inferred a significantly reduced Re dipole moment, and long-range order compatible with an antiferromagnet, non-collinear motif. To interpret the experimental findings, we present a model wavefunction for Re ions derived from the crystal field potential, Coulomb interaction, and spin-orbit coupling that fully respects the symmetry of the low-temperature ordered state. It is used to calculate in analytic form all multipole moments visible in neutron and resonance enhanced x-ray diffraction. A minimal model consistent with available neutron diffraction data predicts significant multipolar moments up to the hexadecapole, and, in particular, a dominant charge-like quadrupole moment. Calculated diffraction patterns embrace single crystal x-ray diffraction at the Re L-edge, and renewed neutron diffraction, to probe the presumed underlying multipolar order.