Antiferromagnetism inYBa2Cu3O6+x

Neutron diffraction has been used to study antiferromagnetic ordering in $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$ as a function of $x$. Evidence for such ordering has been observed only in the tetragonal, nonsuperconducting phase ($x\lesssim 0.4$). The magnetic origin of the superlattice reflections has been confirmed with polarized beam measurements. A single antiferromagnetic structure was observed throughout the ordered phase, with a maximum Néel temperature of ∼500 K and average ordered moment of ${(0.66\mathrm{}\pm 0.07)}_{\mathrm{\mu }\mathit{B}}$ per magnetic Cu atom at $x\approx 0$. Magnetic susceptibility measurements suggest that two-dimensional correlations are strong, as in ${\mathrm{La}}_2\mathrm{Cu}{\mathrm{O}}_{4-y}$, and may survive into the orthorhombic phase.