Antiferromagnetic long-range order in the 5 d 1 double-perovskite Sr 2 MgReO 6

The double-perovskite ${A}_{2}B{B}^{\ensuremath{'}}{\mathrm{O}}_{6}$ with heavy transition metal ions on the ordered ${B}^{\ensuremath{'}}$ sites is an important family of compounds to study the interplay between electron correlation and spin-orbit coupling. Here we prepared high-quality ${\mathrm{Sr}}_{2}{\mathrm{MgReO}}_{6}$ powder and single-crystal samples and performed nonresonant and resonant synchrotron x-ray diffraction experiments to investigate its magnetic ground state. By combining the magnetic susceptibility and heat capacity measurements, we conclude that ${\mathrm{Sr}}_{2}{\mathrm{MgReO}}_{6}$ exhibits a layered antiferromagnetic order at temperatures below $\ensuremath{\sim}55$ K with a propagation vector $\mathbit{q}=(001)$, which contrasts the previously suspected spin-glass state. Our works clarify the magnetic order in ${\mathrm{Sr}}_{2}{\mathrm{MgReO}}_{6}$ and demonstrate it as a candidate system to look for magnetic octupolar orders and exotic spin dynamics.