Evidence for Antiferromagnetic Order in Bi2Sr2CuO6Phase with Stoichiometric Cation Composition

We have succeeded in synthesizing the insulating phase of Bi 2 Sr 2 CuO 6+δ (Bi2201) with the stoichiometric cation composition by use of a heat treatment technique in an evacuated tube with titanium powders. The excess oxygen content δ and the average valence of Bi were determined electrochemically by the coulometric titration method. The value of δ in the insulating phase was found to be 0.02. The hole concentration h was also estimated with values of δ and the average valence of Bi in Bi2201. As a result, temperature dependence of resistivity and h dependence of Tc and Meissner volume fraction indicated behaviors similar to those of other high-Tc systems. The antiferromagnetic order of Cu 2+ spins in the insulating Bi2201 phase has been confirmed by nuclear magnetic resonance. Thus, we can obtain the three distinct electronic states observed in high-Tc oxides, i.e., over-doped metallic, superconducting, and antiferromagnetic phases in Bi2201 compounds by changing only the oxygen content. The static parameters of the hyperfine field and the electric field gradient at Cu sites in Bi 2 Sr 2 CuO 0.62 were found to be almost comparable to those of other antiferromagnetic phases of high-Tc oxides.