Long-range antiferromagnetic order of the Cu in oxygen-deficientRBa2Cu3O6+x

Abstract

We have employed polarized and unpolarized neutron-diffraction techniques on both powders and single crystals to establish the nature of the magnetic order of the Cu ions in oxygen-deficient (nonsuperconducting) $R{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$ ($R=\mathrm{Y},\mathrm{N}\mathrm{d}$). Magnetic Bragg peaks of the type ($\frac{h}{2},\frac{k}{2},l$) are observed that yield a magnetic structure in which the Cu spins are coupled antiferromagnetically both in the Cu-O planes as well as along the tetragonal $c$ axis, with the spin direction in the tetragonal plane. The Néel temperature is very sensitive to the oxygen content, with $T_{N\left(x\sim 0\right)}\approx 500$ K, while the spin configuration is independent of $x$.