Intrinsic Triple Order in A-site Columnar-Ordered Quadruple Perovskites: Proof of Concept.

There is an emerging topic in the science of perovskite materials: A-site columnar-ordered A ₂ A'A''B ₄ O ₁₂ quadruple perovskites, which have an intrinsic triple order at the A sites. However, in many examples reported so far, A' and A'' cations are the same, and the intrinsic triple order is hidden. Here, we investigate structural properties of Dy ₂ CuMnMn ₄ O ₁₂ (1) and Ho ₂ MnGaMn ₄ O ₁₂ (2) by neutron and X-ray powder diffraction and prove the triple order at the A sites. The cation distributions determined are [Ho ₂ ] _A [Mn] _A' [Ga _0.66 Mn _0.34 ] _A'' [Mn _3.66 Ga _0.34 ] _B O ₁₂ and [Dy ₂ ] _A [Cu _0.73 Mn _0.27 ] _A' [Mn _0.80 Dy _0.20 ] _A'' [Mn _1.89 Cu _0.11 ] _B1 [Mn ₂ ] _B2 O ₁₂ . There are clear signatures of Jahn-Teller distortions in 1 and 2, and the orbital pattern is combined with an original type of charge ordering in 1. Columnar-ordered quadruple perovskites represent a new playground to study complex interactions between different electronic degrees of freedom. No long-range magnetic order was found in 2 by neutron diffraction, and its magnetic properties in low fields are dominated by an impurity with negative magnetization or magnetization reversal. On the other hand, 1 shows three magnetic transitions at 21, 125, and 160 K.
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