The first synthesis of the layered manganite (La,Ba)3Mn2O7−δvia a ‘cuprate-like’ low valent intermediate

Abstract

The synthesis of La_1+xBa_2−xMn₂O₆ (0.2 ≤ x ≤ 0.4) under reducing conditions is reported. Neutron powder diffraction studies indicate an A-site ordered, oxygen deficient bilayer Ruddlesden–Popper structure. La³⁺ ions preferentially occupy oxygen vacant layers within the perovskite bilayers, leading to a structure analogous to the cuprate superconductor La_1.85Ba_0.15CaCu₂O_6+γ, with “MnO₂” layers constructed from corner-linked square pyramidal MnO₅ units. Magnetic measurements suggest that no long range magnetic order exists in this mixed Mn²⁺/Mn³⁺ system. Significantly, the low temperature oxidation of this phase leads to the synthesis of La_1+xBa_2−xMn₂O_6.95, which constitutes the first isolation of a complete barium analogue of La_1+xSr_2−xMn₂O₇, the important low field colossal magnetoresistive material. Neutron diffraction data confirm the retention of A-site order and a change in Jahn–Teller distortion. Low temperature neutron data and magnetic susceptibility suggest canted A-type antiferromagnetic order.