Antiferromagnetic ordering in a 90 K copper oxide superconductor

Using elastic neutron scattering, we evidence a commensurate antiferromagnetic Cu(2) order (AF) (TN~330 K, μ~0.14 μB) in the superconducting (SC) high-Tc cuprate YBa₂(Cu_1-yCoy)₃O_7+δ (y=0.013,Tc=93 K). We find that the spin excitation spectrum is still dominated by a magnetic resonance peak at 41 meV as in the Co-free system, but with a reduced spectral weight. The substitution of Co leads to a state where AF and SC cohabit at a microscopic scale, without any strong interference.