Coexisting commensurate and incommensurate magnetic orders in the double double perovskite CaMnCoWO6

Abstract

A new double double perovskite of ideal composition CaMnCoWO6 has been synthesised at high pressure. The structure is tetragonal (P42/n, a=7.6651(3), c=7.6822(3) Å) and disorder between A-site Mn2+ and B-site Co2+ leads to a Co-rich off-stoichiometric composition CaMn0.8Co1.2WO6 [Ca(Mn0.65Co0.35) (Co0.86Mn0.14)WO6]. An unusual combination of commensurate and incommensurate spin orders (A-site Mn/Co spins with propagation vector (0.5 0.5 0.5) and B-site Co/Mn spins with (0.5 0.42 0.5)) is observed below a magnetic transition at TC=18 K. This is the first discovery of complex magnetism in the double double perovskite family.