Superconductivity and Magnetism of the New Heavy Fermion Superconductors UM₂Al₃(M=Ni, Pd)–²⁷Al NMR Study–

Abstract

The magnetic and superconducting properties of the new heavy fermion superconductors (HFS), UNi 2 Al 3 and UPd 2 Al 3 have been investigated by 27 Al NMR. The magnetic ordering is unambiguously identified by a significant increase of 27 Al linewidth below T N =4.6 K and an enhancement of the nuclear-spin-lattice relaxation rate 27 (1/ T 1 ) around T N in UNi 2 Al 3 and by a gradual increase of the linewidth and a distinct drop of 27 (1/ T 1 ) below T N =14 K in UPd 2 Al 3 . Below T c =0.9 K in a magnetic field of 2.8 kOe, no anomalies of 1/ T 1 and Knight shift have been observed in UNi 2 Al 3 , whereas the superconductivity in UPd 2 Al 3 is well evidenced by a significant decrease of both 1/ T 1 and Knight shift below T c =1.8 K in 4.9 kOe. The behavior of 1/ T 1 in UPd 2 Al 3 , with no coherence peak just below T c , is well described down to 0.65 K by a model of gap zeros on lines at the Fermi surface, being quite similar to the behavior in HFS reported thus far.