Magnetic order and 5d1 multipoles in a rhenate double perovskite Ba2MgReO6

TL;DR

This study investigates the structural and magnetic properties of Ba2MgReO6, revealing complex multipole interactions and challenging previous assumptions about its phase transitions, supported by x-ray and neutron diffraction data.

Contribution

It provides a new model for Re wave functions and clarifies the nature of multipoles and magnetic order in Ba2MgReO6, contrasting prior interpretations of structural transitions.

Findings

Structural transition not driven by T2g quadrupoles

Magnetic order involves two propagation vectors

Predicted electronic quadrupole and magnetic dipole signatures

Abstract

Structural and magnetic transitions in a double perovskite hosting 5d1 Re ions are discussed on the basis of recently published high-resolution x-ray diffraction patterns [D. Hirai, et al., Phys. Rev. Res. 2, 022063(R) (2020)]. A reported structural transition below room temperature, from cubic to tetragonal symmetry, appears not to be driven by T2g-type quadrupoles, as suggested. A magnetic motif at lower temperature is shown to be composed of two order parameters, associated with propagation vectors k = (0, 0, 1) and k = (0, 0, 0). Findings from our studies, for structural and magnetic properties of Ba2MgReO6, surface in predicted amplitudes for x-ray diffraction at rhenium L2 and L3 absorption edges, and magnetic neutron Bragg diffraction. Specifically, entanglement of anapole and spatial degrees of freedom creates a quadrupole in the neutron scattering amplitude. It would be excluded in an unexpected scenario whereby the rhenium atomic state is a manifold. Also, a chiral signature visible in resonant x-ray diffraction will be one consequence of predicted electronic quadrupole and magnetic dipole orders. A model Re wave function consistent with all current knowledge is a guide to electronic and magnetic multipoles engaged in x-ray and neutron diffraction investigations.