Crystal and magnetic structures of a new high pressure S = ½ Re6+ double perovskite Mn2MgReO6

Introducing rock-salt B-site ordering of a non-magnetic cation (here Mg2+) and a S = ½ cation with strong spin-orbital coupling (Re6+) creates geometrically frustrated A2MgReO6 double perovskite (DPv) materials in which interesting phenomena can emerge e.g. multipolar orders in Ba2MgReO6. We have used high pressure to prepare a new Mn2MgReO6 DPv material combining magnetic A-site Mn2+ and the geometrical frustrated BB’ sublattices of A2MgReO6 materials. Magnetic susceptibility data show a ferrimagnetic transition near TC1 = 75 K and a very weak anomaly at TC2 = 40 K. The Weiss/Curie temperature ratio is not consistent with a highly frustrated ground state, and indicates that Mn-Re interactions likely outweigh the expected geometric frustration in the B’ = Re sublattice, but hysteresis measurements reveal an unusual temperature variation that may indicate different ordering temperatures or saturation behaviour for Mn and Re spins. Neutron data from WISH are necessary to study the crystal and magnetic structures of Mn2MgReO6. Neutrons will give accurate atom positions, bond distances and structural distortions around the Mn-site, and enable us to solve the magnetic structure and its evolution below 75 K.