Magnetization in the superconducting state of UPt ₃ from polarized neutron diffraction

The heavy-fermion superconductor UPt ₃ is thought to have odd parity, a state for which the temperature dependence of the spin susceptibility is an important signature. In order to address conflicting reports from two different experiments, the NMR Knight shift and measurements of the anisotropy of the upper critical field, we have measured the bulk susceptibility in a high-quality single crystal using polarized neutron diffraction. A temperature-independent susceptibility was observed for Ha through the transitions between the normal state and the superconducting A, B, and C phases, consistent with odd-parity, spin-triplet superconductivity.