NMR Study of Caged Cubic Compound NdTr 2 Al 20 (Tr = Ti and V)

We report on the results of the nuclear magnetic resonance (NMR) measurements of caged cubic compounds NdT r 2 Al 20 (T r = Ti and V) in order to investigate the microscopic electronic states at low temperatures.For both compounds, the 27 Al Knight shift, 27 K, obeys a Curie-Weiss law, which is scaled to the magnetic susceptibility.The magnitude of 27 K at the 96g site is larger than that at the 48 f site, indicating larger hyperfine coupling with Nd 4 f moments at the 96g site. 27K in NdV 2 Al 20 are clearly larger than that in NdTi 2 Al 20 .Also, the nuclear spin-lattice relaxatuion rate 1/T 1 's for both sites remain constant at high temperature region, which is reminiscent of the relaxation mechanism dominated by the exchange interaction of the 27 Al nucleus with fluctuating Nd-4 f moments.Upon cooling, 1/T 1 decreases gradually and shows a gap-like behavior at low temperatures, where the magnitude of gap is smaller than the crystal-electric-field (CEF) excitation gap estimated from the specific heat measurements.