Ground State Properties of the A-site Ordered Manganites, RBaMn₂O₆ (R = La, Pr and Nd)

Abstract

The most significant structural feature of the A-site ordered manganese perovskites, RBaMn₂O₆, is that the MnO₂ square sublattice is sandwiched by two types of rock-salt layers, RO and BaO, with much different sizes and consequently the MnO₆ octahedron itself is distorted in a noncetrosymmetric manner. The structures and electromagnetic properties of RBaMn₂O₆ (R = La, Pr and Nd) have been investigated. They have tetragonal structures with no tilt of MnO₆ octahedra and show ferromagnetic metal transitions. The ground state is a coexistence of ferromagnetic metal and antiferromagnetic charge-orbital ordered phases for LaBaMn₂O₆ and A-type antiferromagnetic metal for PrBaMn₂O₆ and NdBaMn₂O₆. These ground state behaviors are explained by the effect of Mn–O distance on the bandwidth and the layer structure with the RO–MnO₂–BaO–MnO₂ stacking along the c-axis.