Magnetic ordering in the high-temperature superconductor ${\mathrm{ErBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$

Neutron diffraction has been used to reexamine the magnetic ordering in the high-temperature superconductor, ${\mathrm{ErBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. A composite sample of five single crystals has been used for this investigation. The anomaly in the specific heat at 0.55 K is found to correspond to the formation of a three-dimensional, antiferromagnetic long-range-ordered state. This finding is in disagreement with an earlier measurement by Lynn et al., [Phys. Rev. B 36, 2374 (1987)] which suggested a two-dimensional magnetic structure.