Magnetic structure ofErNi2B2C

Neutron-diffraction techniques have been used to study the magnetic structure of the superconductor ${\mathrm{ErNi}}_2$ ${\mathrm{B}}_2$C (${\mathit{T}}_{\mathit{c}}$=11 K). The experimental results, obtained on single crystals, show that below approximately 7 K this compound is in an incommensurate modulated antiferromagnetic state, with wave vector 0.553a*, that coexists with superconductivity. The field dependence of the magnetic structure of this compound was studied at 5.5 K as a function of an externally applied magnetic field both along the b and c axes of the tetragonal structure.