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

Abstract

Both magnetic and superconducting characteristics of the new heavy fermion superconductors (HFS), UNi 2 Al 3 and UPd 2 Al 3 have been investigated extensively by means of 27 Al NMR and NQR. Systematic studies of the nuclear-spin-lattice relaxation time T 1 , the Knight shift and the spectrum of 27 Al have revealed different types of magnetic fluctuations and spin structure between these two compounds. UNi 2 Al 3 shows a band-type itinerant antiferromagnetic behavior, while UPd 2 Al 3 belongs to a heavy fermion antiferromagnet with an ordinary size of U-derived moment. In the superconducting state, the relaxation behavior in UPd 2 Al 3 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.