Anisotropic Spin Fluctuations in Heavy-Fermion Superconductor NpPd5Al2

Abstract

We present 27 Al NMR measurements of the Knight shift and nuclear spin–lattice relaxation rate 1/ T 1 in the normal state for a single crystal of the heavy-fermion superconductor NpPd 5 Al 2 ( T c = 4.9 K). We report here that 1/ T 1 shows a large anisotropy with a different temperature dependence for H ∥ a and H ∥ c . 1/ T 1 for H ∥ c shows a power-law temperature dependence ∼ T 0.38 , while 1/ T 1 for H ∥ a shows a T -linear dependence at low temperatures in fields well above H c2 . From the analysis of 1/ T 1 , X Y -type anisotropy of AFM spin fluctuations is found to become prominent below 20 K.