Excess Oxygen Doping in Single Crystals of La 2-xBixCuO 4+ δ with or without Macroscopic Phase Separation

Systematic heat treatments have been performed using single crystals of La 2- x Bi x CuO 4+δ to study the effect of oxygen doping on the phase stability as well as the three-dimensional magnetic order. For La 2 CuO 4+δ , the analysis of magnetic susceptibility peak near the Neel temperature T N revealed that the continuous decrease of T N upon doping is terminated at 280 K. The further doping additionally induces the previously reported macroscopic phase separation accompanying an antiferromagnetic phase with T N =265 K and a superconducting one with T C ≤35 K. On the other hand, for La 2- x Bi x CuO 4+δ with x ∼0.05 no macroscopic phase separation was observed up to δ≈0.02. Upon the oxygen doping, the T N continuously decreases from 310 K to below 10 K only by the heat treatment. The scaling behavior of magnetic ssusceptibility previously studied by the powder sample of La 2- x SrxCuO 4+δ was reexamined in this system.