X-ray-scattering study of copper magnetism in nonsuperconducting PrBa2Cu3O6.92

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 PrBa2Cu3 O6.92 with x-ray photon energies tuned in the vicinity of the Cu K edge. Th e high wave-vector resolution enabled us to observe an incommensurate doubl e-Q Cu spin structure below T-Pr = 19 K that forms as a result of coupling between the magnetically ordered Cu and Pr sublattices. Above T-Pr, the Cu ordering is commensurate, ruling out static spin-charge stripe order as an explanation for the absence of superconductivity in this material.