Magnetic study of the UPt3 superconducting phases

In order to distinguish the UPt₃ superconducting (s.c.) phases we have studied their magnetic properties at low fields in a SQUID magnetometer and up to fields >H_c2(0) with a capacitive torque-meter. With the SQUID we measure the magnetic penetration depth and find the second s.c. transition at T_c^? when the field is applied along the c-axis, but not with . This result, combined with power-law behavior at low temperature T, is most consistent with the two-dimensional E_2u s.c. order parameter. Below 20 mK we find an additional diamagnetic signal that we ascribe to the normal state magnetism. In high fields our torque measurements show a kink of the perpendicular magnetization component at the B–C phase line, pointing to an enhanced Ginzburg–Landau parameter in the C phase.