Hydrothermal synthesis, magnetism and resistivity of orthorhombic perovskite manganates Y_1-xCa_xMnO₃ (x = 0, 0.07, 0.55, 0.65)

Orthorhombic Y_1-xCa_xMnO₃ (x = 0, 0.07, 0.55, 0.65) crystals were successfully prepared in one step via the mild hydrothermal synthesis, and the magnetic and electric properties were investigated in detail. The formation and composition of Y_{1- x}Ca_xMnO₃ crystals mainly depend on the molar ratios of starting materials, reaction temperature and alkalinity of the reaction system. The magnetic properties of Y_1-xCa _xMnO₃ strongly depend on the doping content of Ca. Y _1-xCa_xMnO₃ (x = 0, 0.07 and 0.55) demonstrate the spin-glass-like behaviors. Y_1-xCa _xMnO₃ (x = 0.55 and 0.65) show charge ordering and antiferromagnetic transition, and the antiferromagnetic state is stabilized by charge ordering. The signal of charge ordering transition of Y_{1- x}Ca_xMnO₃ (x = 0.65) is very strong and its magnetization increases significantly below 46 K due to the Dzyaloshinsky-Moriya (DM) anisotropic super-exchange interaction. The charge transport of samples that have charge ordering takes on the behavior of semiconductors. They show a small magnetoresistance effect. Their electric conduction mechanism accords with the variable-range hopping mode of highly correlated electrons.