Aサイト秩序型/無秩序型ベロブスカイトMn酸化物属BaMn_2O_6/R_(0.5)Ba_(0.5)MnO_3の構造と物性

摘要

The structures and electromagnetic properties of/I-site ordered/disordered perovskite manganites, R_(0.5)Ba_(0.5)MnO_3 (R = Y and rare earth elements), have been investigated. RbaMn_2O_6 exhibits remarkable features; (1) the charge/orbital order (CO) transition at relatively higher temperatures far above 300 K, (2) a new stacking variation of the CE-type CO with a 4-fold periodicity along the c-axis, (3) the presence of structural transition possibly accompanied by d_(x2-y2) orbital order, (4) electronic phase separation. These novel structural and electromagnetic properties are discussed in terms of the structural characteristic that the MnO_2 square sub-lattice is sandwiched by two types of rock-salt layers, RO and BaO with different lattice sizes, which introduces a strong frustration to the MnO_2 sub-lattice. In R_(0.5)Ba_(0.5)MnO_3 with a primitive cubic perovskite cell, on the other hand, the magnetic glassy states are dominant as the ground state. A peculiar behavior, the steplike ultrasharp magnetization and resistivity changes, has been observed in Pr_(0.5)Ba_(0.5)MnO_3.