Equilibrium properties of the fluxoid lattice in single-crystal niobium. II. Small-angle neutron-diffraction measurements

A small-angle neutron-diffraction technique has been used to measure several properties of the flux-line lattice (FLL) in a single-crystal sphere of pure niobium. For applied fields parallel to several crystallographic directions in the (100) and (11̄0) planes, the low-field mixed state and intermediate mixed state were investigated. From these results, the orientation dependence of the low-field critical parameters Hc1 and B₀ are deduced. The consistency of these results is verified by comparison with direct measurements of the equilibrium misalignment angle between the applied-field direction and the fluxoid axes. In addition, results are reported which extend the available information concerning correlations between the FLL and crystal lattice (CL) symmetry properties.