Measurements of both the lower and upper critical fields along all three principal axes of the heavy-fermion superconductor ${\mathrm{UPt}}_3$ have been performed. A kink in the temperature dependence of the lower critical field, ${\mathit{H}}_{\mathit{c}1}$, is observed for all three orientations, which is in agreement with a recent theory by Hess, Tokuyasu, and Sauls. Also, an anisotropy of the temperature dependence of the lower critical field is observed at low temperatures (T<290 mK). The Landau-Ginzburg parameters are estimated from the experimental results.

• Received 8 February 1991

DOI:https://doi.org/10.1103/PhysRevB.43.13720