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 PrBa2Cu3O6.92 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-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.

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 ${T}_{\mathrm{Pr}}=19$ 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.

Magnetic flux turbulence was observed in single crystals of NdBa2Cu3O6+x near-optimally doped (x approximate to 1) and underdoped YBa2Cu3O6-x (x=0.50,0.82) using magneto-optical imaging. Such turbulent phenomena have so far been reported only for YBa2Cu3O6+x high-quality single crystals with optimal doping. The crystals were also characterized in terms of critical current density j(c), anisotropy gamma, and oxygen content/superstructure. The influence of these parameters on the turbulent behavior is discussed. [S0163-1829(99)50506-7].

We describe a neutron-diffraction study of the low-temperature magnetic ordering in single crystals of NdBa2Cu3O6+x. We investigated a superconducting crystal (T-c=95.5 K), and two nonsuperconducting crystals (x approximate to 0.1). The two nonsuperconducting crystals differed in their Cu sublattice magnetic ordering. One (A) exhibited the simple AFI antiferromagnetic spin structure down to the lowest attainable temperature (0.3 K), while the other (B) began to reorder into the AFII phase below 30 K. We observed long-range antiferromagnetic ordering of the Nd sublattice in all three crystals, but in crystal B the Nd ordering was of very short range in the c direction. The onset of Nd ordering produced no detectable changes in the: CU ordering in the nonsuperconducting crystals, and from this we place an upper limit of 0.05 meV on the strength of any Nd-Cu pseudodipolar magnetic coupling. The ordered arrangements of the Nd moments refined from the diffraction intensities agree broadly with those deduced previously from neutron powder diffraction studies, but differ in some of the details. [S0163-1829(99)02826-X].