NEUTRON-DIFFRACTION STUDY OF ANTIFERROMAGNETIC ORDER IN THE MAGNETIC SUPERCONDUCTOR ERNI2B2C

We have carried out powder-neutron-diffraction studies of the antiferromagnetic order that develops below TN=6.8 K in the magnetic superconductor (Tc=11 K) ErNi2B2C. The antiferromagnetic structure is associated with spins on the Er atoms, which order in a transversely polarized planar sinusoidal structure propagating along the a or b axis in equal domains, with the Er moments parallel to the b or a axis, respectively. Third and fifth harmonics of the sine wave are observed at low temperatures, indicating a squared-up sine wave, with a low-temperature amplitude of 7.8B/Er atom. There is also evidence of an induced moment of -0.35B on the Ni ions. A similar study of the isostructural compound YNi2B2C revealed no magnetic peaks (<0.13B) developing down to 0.3 K for Q values less than 1.6 A-1. © 1995 The American Physical Society.