Magnetic order of Dy in DyBa2Cu3O7

Abstract

Neutron diffraction has been used to study the magnetic fluctuations and long range order of the Dy ions in single crystals of superconducting DyBa₂Cu₃O₇. The temperature dependence of the rod of scattering, characteristic of 2D behavior, has been measured above and below the 3D Néel temperature (T_N ≂ 0.9 K). This rod intensity is observed to increase as the temperature decreases until T_N is reached, and then the intensity decreases rapidly below T_N. The 2D magnetic correlation length, which is obtained from measurements of the width of the rod, grows continuously with decreasing temperature, then reaches a resolution‐limited maximum at the Néel temperature when long range magnetic order sets in. At low T, two separate types of simple 3D antiferromagnetic structures are found, one characterized by a wave vector of (1/2 1/2 0), and the other by (1/2 1/2 1/2). We believe the two types of order occur because the (dipolar) energies for these two configurations are nearly identical. This behavior is analogous to the 2D and 3D magnetic order of Er observed in ErBa₂Cu₃O₇.