Neutron-diffraction study of antiferromagnetic order in the magnetic superconductor ErNi₂B₂C

Abstract

We have carried out powder-neutron-diffraction studies of the antiferromagnetic order that develops below T_N=6.8 K in the magnetic superconductor (T_c=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 7.8μ_B/Er atom. There is also evidence of an induced moment of -0.35μ_B on the Ni ions. A similar study of the isostructural compound YNi₂B₂C revealed no magnetic peaks (μ < 0.13μ_B) developing down to 0.3 K for Q values less than 1.6 A^-1.