Two-dimensional bilayer magnetic order of Dy ions in Dy2Ba4Cu7O15

Neutron scattering has been used to investigate the magnetic ordering of Dy ions in the Dy2Ba4Cu7O15 material. A modulated saw-tooth scattering profile is observed, indicative of a coupled-bilayer two-dimensional (2D) system in which the Dy spins within the a-b planes are coupled antiferromagnetically, with TN=1.25 K. The 2D order originates from the crystal structure, as the c-axis spacing of the magnetic ions is ∝3 times the a-b spacing. In addition, every other a-b plane is shifted along the b-axis by b/2, causing a cancellation of magnetic interactions which completely isolates the bilayers. We anticipate that a similar coupled-bilayer 2D behavior should occur in other R2Ba4Cu7O15 (R=rare earth element, except Er) in which nearest-neighbor spins within the a-b plane are coupled antiferromagnetically. (orig.)