Structures and Electromagnetic Properties of New Metal-Ordered Manganites: RBaMn₂O₆ (R=Y and Rare-Earth Elements)

Abstract

New metal-ordered manganites RBaMn₂O₆ can be classified into three groups based on the structural and electromagnetic properties measured. The first group (R=Tb, Dy and Ho) shows three successive phase transitions, namely, structural, charge/orbital order (CO) and antiferromagnetic order (AF) transitions on cooling, as observed in YBaMn₂O₆. The second group (R=Sm, Eu and Gd) exhibits a CO transition, followed by an AF transition. The third group (R=La, Pr and Nd) exhibits a metallic ferromagnetic transition, followed by an A-type AF transition in PrBaMn₂O₆ and NdBaMn₂O₆. Compared with metal-disordered (R_0.5³⁺A_0.5²⁺)MnO₃, RBaMn₂O₆ has two remarkable features: (1) the high CO transition temperature (T_CO) above 340 K and (2) the presence of a structural transition above T_CO in the first group. These are closely related to the structural feature that the MnO₂ sub-lattice is sandwiched by two types of rock-salt layers, RO and BaO, with different lattice sizes.