We re-analyze Nuclear Magnetic Resonance (NMR) spectra observed at low temperatures and high magnetic fields in the field-induced B phase of CeCoIn 5. The NMR spectra are consistent with incommensurate antiferromagnetic order of the Ce magnetic moments. However, we find that the spectra of the In(2) sites depend critically on the direction of the ordered moments, the ordering wavevector and the symmetry of the hyperfine coupling to the Ce spins. Assuming isotropic hyperfine coupling, the NMR spectra observed for H ∥ are consistent with magnetic order with wavevector Q=π(1+δ/a, 1/a, 1/c) and Ce moments ordered antiferromagnetically along the  direction in real space. If the hyperfine coupling has dipolar symmetry, then the NMR spectra require Ce moments along the  direction. The dipolar scenario is also consistent with recent neutron scattering measurements that find an ordered moment of 0.15μ B along  and Q n=π(1+δ/a, 1+δ/a, 1/c) with incommensuration δ=0.12 for field H∥[1̄10] . Using these parameters, we find that a hyperfine field with dipolar contribution is consistent with findings from both experiments. We speculate that the B phase of CeCoIn 5 represents an intrinsic phase of modulated superconductivity and antiferromagnetism that can only emerge in a highly clean system.
- Heavy fermion