The magnetic structure of orthorhombic ErNi₂B₂C

In a recent X-ray scattering experiment, it was demonstrated that the magnetic ordering transition of ErNi₂B₂C at 6.0 K is accompanied by a structural distortion, which lowers the crystal symmetry from tetragonal to orthorhombic. In previous neutron magnetic scattering experiments, this lowering of the crystal lattice symmetry was not resolved. Since the magnetic modulations along the a and b crystallographic directions are equivalent in tetragonal, but not in orthorhombic systems, the magnetic structure determinations based on neutron data remained incomplete. We have performed a high-resolution non-resonant magnetic X-ray scattering experiment on a single crystal of ErNi₂B₂C to determine the magnetic structure. The magnetic modulation wave vector is (0.5537, 0, 0) and lies along the long side of the orthorhombic basal plane.