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), UNi₂Al₃ and UPd₂Al₃ have been investigated extensively by means of ²⁷Al NMR and NQR. Systematic studies of the nuclear-spin-lattice relaxation time T₁, the Knight shift and the spectrum of ²⁷Al 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.