Effect Of B-Site Order-Disorder In The Structure And Magnetism Of The New Perovskite Family La2mnb'O-6 With B' = Ti, Zr, And Hf

In this work, we report the synthesis as well as the structural and magnetic characterization of the three perovskites La2MnB'O-6 (B' = Ti, Zr, and Hf). Interestingly, only La2MnTiO6 crystallizes in the monoclinic double perovskite space group P2(1)/n, with a complete rocksalt order of the B-site cations, whereas La2MnZrO6 and La2MnHfO6 crystallize in the orthorhombic simple perovskite space group Pbnm, with complete disorder in the B site. Moreover, the magnetic susceptibility at low temperatures shows clear antiferromagnetic transitions below 10 K for the three compounds, but only the Ti-based perovskite has long-range magnetic ordering. The latter compound has an antiferromagnetic type-II structure described by the PS-1 magnetic space group, while the other two have a spin-glass behavior below the transition temperature due to both spin disorder and competing super-exchange interactions in the systems. This is the first time that two of the three studied compounds were synthesized (B' = Zr and Hf) and the first time that the whole series is described in thorough detail using symmetry-adapted refinements and magnetic crystallography.