Structure of the flux lines lattice in NbSe2: Equilibrium state and influence of the magnetic history

We have performed small-angle neutron scattering of the flux line lattice (FLL) in a Fe-doped ${\text{NbSe}}_{2}$ sample which presents a large peak effect in the critical current. The scattered intensity and the width of the Bragg peaks of the equilibrium FLL indicate an ordered structure in the peak effect zone. The history dependence in the FLL structure has been studied using field-cooled and zero\char21{}field-cooled procedures, and each state shows the same intensity of Bragg scattering and good orientational order. These results strongly suggest that the peak effect is unrelated to a bulk-disordering transition and confirm the role of a heterogeneous distribution of screening current.