Nonlocal corrections to the London model are used to describe vortex lattices in ${\mathrm{LuNi}}_2$${\mathrm{B}}_2$C. Within this scheme in fields along the c axis, vortices should form a square lattice (rotated 45° relative to the crystal axes afandfb) at large fields, should transform to a triangular one at a field ${\mathrm{H}}_2$, and to another triangular lattice at a still lower field ${\mathrm{H}}_1$. We argue that the transition at ${\mathrm{H}}_2$ is of second order, whereas at ${\mathrm{H}}_1$ it is of first order. In tilted fields, ${\mathrm{H}}_2$ is predicted to move to higher fields. Neutron-scattering data for ${\mathrm{ErNi}}_2$${\mathrm{B}}_2$C are discussed.

DOI:https://doi.org/10.1103/PhysRevB.55.R8693