Magnetic properties of heavy fermion superconductors UPt₃ and URu₂Si₂

The effects of the normal state paramagnetism on the superconductivity of UPt₃ and URu₂Si₂ were investigated by means of static magnetization measurements. While the upper critical field of URu₂Si₂ seems to be paramagnetically suppressed, no clear spin reduction is observed in the magnetization curves. The paramagnetic polarization in UPt₃ for H⊥c (H∥c) is as large as (slightly suppressed below) the normal-state value, although the normal state spin susceptibility is considered to be largest for H⊥c. The results of UPt₃ point to an odd-parity pairing with a discernible anisotropy in the pair-spin state.