X-ray-scattering study of copper magnetism in nonsuperconductingPrBa2Cu3O6.92

X-ray magnetic scattering from ordered Cu spins has been observed in a high-$T_c$ compound. The measurements were made on the anomalous cuprate ${\mathrm{PrBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.92}$ with x-ray photon energies tuned in the vicinity of the Cu K edge. The high wave-vector resolution enabled us to observe an incommensurate double-$Q$ Cu spin structure below $T_{\mathrm{Pr}}=19\mathrm{}$ K that forms as a result of coupling between the magnetically ordered Cu and Pr sublattices. Above $T_{\mathrm{Pr}},$ the Cu ordering is commensurate, ruling out static spin-charge stripe order as an explanation for the absence of superconductivity in this material.