Double Double Cation Order in the High‐Pressure Perovskites MnRMnSbO 6

Cation ordering in ABO 3 perovskites adds to their chemical variety and can lead to properties such as ferrimagnetism and magnetoresistance in Sr 2 FeMoO 6 . Through high‐pressure and high‐temperature synthesis, a new type of “double double perovskite” structure has been discovered in the family MnRMnSbO 6 (R=La, Pr, Nd, Sm). This tetragonal structure has a 1:1 order of cations on both A and B sites, with A‐site Mn 2+ and R 3+ cations ordered in columns and Mn 2+ and Sb 5+ having rock salt order on the B sites. The MnRMnSbO 6 double double perovskites are ferrimagnetic at low temperatures with additional spin‐reorientation transitions. The ordering direction of ferrimagnetic Mn spins in MnNdMnSbO 6 changes from parallel to [001] below T C =76 K to perpendicular below the reorientation transition at 42 K at which Nd moments also order. Smaller rare earths lead to conventional monoclinic double perovskites (MnR)MnSbO 6 for Eu and Gd.