Small-angle neutron scattering study of the vortex lattice in superconducting LuNi₂B₂C

We present studies of the magnetic field distribution around the vortices in LuNi₂B₂C. Small-angle neutron scattering measurements of the vortex lattice (VL) in this material were extended to unprecedentedly large values of the scattering vector q, obtained both by using high magnetic fields to decrease the VL spacing and by using higher order reflections. A square VL, oriented with the nearest-neighbor direction along the crystalline [110] direction, was observed up to the highest measured field. The first-order VL form factor, |F(q₁₀)|, was found to decrease exponentially with increasing magnetic field. Measurements of the higher-order form factors, |F(q_hk)|, reveal a significant in-plane anisotropy and also allow for a real-space reconstruction of the VL field distribution.