DC magnetic penetration depth of UPt₃and Sr₂RuO ₄: Implications for the superconducting order parameters

In order to distinguish the superconducting phases of the title compounds we have studied their DC magnetic properties in low fields with a SQUID magnetometer. The magnetic penetration depth of UPt₃ shows the second superconducting transition at T_c- when the field, is applied along the c-axis, but not with H⊥c. This result, combined with a power law behavior of λ at low temperatures, is most consistent with the two-dimensional E_2u order parameter symmetry. Below 20mK we find an additional diamagnetic signal which we ascribe to the normal state magnetism. For Sr₂RuO₄, supposedly a p-wave superconductor, we find a sharp single diamagnetic transition at 1.08 K showing that our sample is of high quality, but there is no indication of an unusual superconducting behavior.