R-site cation randomness effect in thec A-site ordered Y_0.5La_0.5BaMn₂O₆ compound

The R/Ba-ordered and R-site mixed compound Y_0.5La_0.5BaMn₂O₆ has been synthesized in which (Y, La) and Ba are regularly arranged while Y and La randomly occupy the R-site. Y_0.5La_0.5BaMn₂O₆ has a tetragonal unit cell with a space group of P4/mmm. A structural transition between tetragonal and orthorhombic is observed at about 325 K by X-ray powder diffraction (XRD). Thermal magnetic measurement shows the occurrence of an antiferromagnetic transition at the temperature T_N～190 K. Anomalies in magnetization, resistivity and lattice parameters observed around 340 K indicate a charge/orbital order transition accompanying the structural phase transition. R-site randomness effect is discussed to interpret the different properties of Y_0.5La_0.5BaMn₂O₆ between NdBaMn₂O₆ and SmBaMn₂O₆.