Resistivity and magnetic susceptibility of single-crystal $\mathrm{Lu}({\mathrm{Ni}}_{1-x}{\mathrm{Co}}_x{)}_2{\mathrm{B}}_2\mathrm{C}$ $(x=0.0\mathrm{}–0.09)$

Single crystal samples of $\mathrm{Lu}({\mathrm{Ni}}_{1-x}{\mathrm{Co}}_x{)}_2{\mathrm{B}}_2\mathrm{C}$ have been prepared for $x=0\mathrm{}–\mathrm{0.09.}$ In-plane electrical resistivity measurements show that the residual resistivity of these samples increases linearly with x, though by less than is observed for polycrystalline samples. $T_c$ is suppressed by the cobalt substitution (from 16.0 K for $x=0\mathrm{}$ to 9.5 K for $x=0.09),$ though magnetization measurements indicate that this is not due to pair breaking by magnetic impurities. The critical field $H_{C2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ decreases with increasing Co concentration, and has some anisotropy between $H\parallel c$ and $H\perp c.\mathrm{}$ The ratio of the coherence length to the mean-free path $({\xi }_0/l)$ is estimated, and found to be approaching the dirty limit $({\xi }_0/l\gg 1)$ as x increases. These results are discussed with reference to nonlocal effects and the vortex lattice structure of the borocarbides in the mixed state.