Magnetic ordering in the high-temperature superconductor GdBa/sub 2/Cu/sub 3/O/sub 7/

Neutron diffraction has been employed to study the magnetic ordering in the high-temperature superconducting compound GdBa/sub 2/Cu/sub 3/O/sub 7/. The compound is found to undergo an antiferromagnetic transition with the Gd magnetic moments ordering at 2.22 +- 0.07 K. The ordering is shown to be three dimensional with a doubling of the orthorhombic unit in all three directions. An analysis of the intensities of the observed magnetic Bragg reflections shows that the ordered magnetic moment per Gd atom is 7.4 +- 0.6..mu../sub B/ and lies along the c axis of the orthorhombic cell. It is unlikely that dipolar ordering can explain the occurrence of this magnetic phase transition where the system locks into a three-dimensional ordered arrangement at the Neel temperature, since the separation of the Gd atoms along the c axis is approximately three times that along the a,b axes.