Anisotropic Spin Fluctuations in Heavy-Fermion Superconductor NpPd5Al2

We present Al-27 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 NpPd5Al2 (T-c = 4.9 K). We report here that 1/T-1 shows a large anisotropy with a different temperature dependence for H parallel to a and H parallel to c. 1/T-1 for H parallel to c shows a power-law temperature dependence similar to T-0.38, while 1/T-1 for H parallel to a shows a T-linear dependence at low temperatures in fields well above H-c2. From the analysis of 1/T-1, XY-type anisotropy of AFM spin fluctuations is found to become prominent below 20 K.