Structural distortions and consequences for magnetism in the 5d1 double perovskite Pb2MgReO6.

We report here the structural and magnetic characterisation of the high-pressure double perovskite Pb2MgReO6. Our analysis using neutron diffraction demonstrates that the second-order Jahn-Teller Pb2+ cation plays the dominant structural role, preventing the proposed delicate quadrupolar order from emerging. We explore the relationship between related polar and antipolar structural phases in the context of other complex double perovskites. Muon-spin relaxation (µSR) measurements suggest that a short-range ordered state occurs for 11.3 K < T < 30 K, before a collinear AFM state sets in for T < 11.3 K. These findings add to our understanding of the structural behaviour of lead-based perovskites, as well as the sensitivity of multipolar order to site symmetry.