Magnetic short-range order inCuO2planes of high-Tcsuperconductors

The electronic and magnetic structure at the ${\mathrm{CuO}}_2$ planes of high-${\mathit{T}}_{\mathit{c}}$ oxides as a function of hole doping is analyzed. The Emery model is solved in a mean-field approximation that includes spin correlations between copper atoms. It is found that the long-range antiferromagnetic order is destroyed with 0.025 extra holes per unit cell, while the magnetic moments of Cu are slightly reduced in the disordered phase. The antiferromagnetic long-range order is lost by the presence of ferromagnetic Cu-Cu bonds with the bridging oxygen atoms antiferromagnetically aligned with respect to them. For doping doses corresponding to the superconducting phase, the short-range antiferromagnetic correlations between Cu atoms are not completely lost, as is the case experimentally.