Magnetic Properties of the Double Perovskites LaPbMSbO6 (M = Mn, Co, and Ni)

Abstract

New double perovskites LaPbMSbO 6 , where M 2+ = Mn 2+ , Co 2+ , and Ni 2+ , were synthesized as polycrystals by an aqueous synthetic route at temperatures below 1000 ° C. All samples are monoclinic, space group P2 1 /n, as it is observed from Rietveld analysis of X-ray powder diffraction patterns. The distribution of M 2+ and Sb 5+ among the two octahedral sites have 3% of disorder for M 2+ = Ni 2+ , whereas for M 2+ = Mn 2+ and Co 2+ less disorder is found. The three samples have an antiferromagnetic transition, due to the antiferromagnetic coupling between M 2 + through super-superexchange paths M 2+ -O 2- -Sb 5+ -O 2- -M 2+ . Transition temperatures are low: 8, 10 and 17 K for Mn 2+ , Co 2+ , and Ni 2 + respectively, as a consequence of the relatively long distances between the magnetic ions M 2+ . Besides, for LaPbMnSbO 6 a small transition at 45 K was found, with ferrimagnetic characteristics, possibly as a consequence of a small disorder between Mn 2+ and Sb 5+ . This disorder would give additional and shorter interaction paths: superexchange Mn 2+ -O 2- -Mn 2+ .