Magnetic structure of the noncentrosymmetric heavy-fermion superconductor CePt3Si

We have determined the magnetic structure of the noncentrosymmetric heavy-fermion superconductor CePt3Si using elastic polarized neutron scattering with field-projected (longitudinal) XYZ polarization analysis. We find that the magnetic moment has components both in the tetragonal basal plane and along the tetragonal four-fold axis. Such a magnetic structure is not symmetry-allowed if the magnetic phase transition is second order, and may imply that CePt3Si has lower symmetry in the superconducting state than originally thought.