NMR and NQR Studies of Magnetism and Superconductivity in the Antiferromagnetic Heavy Fermion Superconductors UM₂Al₃ (M=Ni and Pd)

Both magnetic and superconducting characteristics of the new heavy fermion superconductors (HFS), UNi2Al3 and UPd2Al3 have been investigated extensively by means of Al-27 NMR and NQR. Systematic studies of the nuclear-spin-lattice relaxation time T1, the Knight shift and the spectrum of Al-27 have revealed different types of magnetic fluctuations and spin structure between these two compounds. UNi2Al3 shows a band-type itinerant antiferromagnetic behavior, while UPd2Al3 belongs to a heavy fermion antiferromagnet with an ordinary size of U-derived moment. In the superconducting state, the relaxation behavior in UPd2Al3 is similar to those observed in the other HFS reported so far, providing an evidence for an unconventional anisotropic superconductivity with line of gap zeros on the Fermi surface as well. Knight shift has been found to decrease considerably below T(c), showing that the pseudo spin is well defined, not affected by the impurity scattering