Magnetic order and evolution of the electronic state aroundx=0.12 in La2?x Ba x CuO4 and La2?x Sr x CuO4

Muon spin rotation (μ+SR) measurement provides clear evidence of the antiferromagnetic order of Cu moments below 35 K for La2−xBaxCuO4 and below 15 K for La2−xSrxCuO4 in the narrow range ofx where the high-Tc superconductivity (SC) is suppressed remarkably. The results suggest that the change of the electronic state coupled with the lattice instability is relevant to the local suppression of SC and freezing of spin fluctuations of the Cu moment.