Magnetic ordering in the high-temperature superconductor GdBa₂Cu₃O₇

Neutron diffraction has been employed to study the magnetic ordering in the high-temperature superconducting compound GdBa₂{Cu}₃O₇. 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±{}0.6μB 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 N\'eel temperature, since the separation of the Gd atoms along the c axis is approximately three times that along the a,b axes.