Exotic magnetism and spin-orbit-assisted Mott insulating state in a 3d−5d double perovskite

The magnetic structure of Ca2MnReO6 double perovskite is investigated by neutron powder diffraction and bulk magnetization, showing dominant noncollinear Mn magnetic moments [4.35(7)μB] that are orthogonally aligned with the small Re moments [0.22(4)μB]. Ab initio electronic structure calculations show that the strong spin-orbit coupling for Re 5d electrons combined with a relatively modest on-site Coulomb repulsion (UeffRe≳0.6 eV) is sufficient to render this material insulating. This is a rare example of spin-orbit-assisted Mott insulator outside the realm of iridates, with remarkable magnetic properties.