2-DIMENSIONAL ANTIFERROMAGNETIC CORRELATIONS IN THE OXYGEN-DOPED 2-1-4-TYPE CUPRATES

Heat treatments on a single crystal of La1.95Bi0.05CuO4 introduce exce ssive oxygen ions without macroscopic phase separation. Precise determ ination of the change in the oxygen content by weighting the annealed sample showed that the effective hole-doping rate can be controlled co ntinuously from 0 to 0.015, where the three-dimensional Neel order dim inishes and the spin-glass phase appears. Neutron scattering experimen ts were performed using an identical single crystal at different dopin g rates to study the instantaneous two-dimensional antiferromagnetic c orrelations.