Si-NMR study of antiferromagnetic heavy-fermion compounds CePd2Si2 and CeRh2Si2

We report Si-NMR studies on the magnetic property of pressure-induced superconductors CePd2Si2 and CeRh2Si2, which exhibit antiferromagnetic (AF) order with the Neel temperature T-N = 10 K and 36 K at ambient pressure, respectively. The NMR results in CePd2Si2 are consistent with those obtained from the previous neutron-diffraction (ND) experiments. On the other hand, the NMR study in oriented powder CeRh2Si2 has revealed that the spectrum splits into two peaks due to the onset of the AF order with the wave vector of q(1) =( 1/2 1/2 0) below T-N1 = 36 K and each peaksplits further into two peaks below T-N2 = 25 K due to the formation of AF domains with q(2) = (1/2 1/2 1/2). The saturation moment M-AF(NMR) = 0.36 and 0.22 mu(B) estimated from NMR are significantly smaller than M-AF(ND) = 1.86 and 1.69 mu(B) from ND. From this discrepancy in the sizes of M-AF, it is proposed that a correlation time in fluctuations of f-electron moments is longer than the characteristic time of observation for thermal neutrons but shorter than that for NMR. This probe dependence of M-AF was observed in the uranium heavy-fermion (HF) compounds UPt3 and URu2Si2. From the temperature dependence of the nuclear spin-lattice relaxation rate 1/T-1 in the paramagnetic state, the Kondo temperature T-K in CeRh2Si2 is estimated to be around similar to 100 K, much higher than T(K)similar to 12 K in CePd2Si2. The 1/T-1's in both the compounds decrease markedly below T-N, followed by a T1T= constant behavior far below T-N. From the latter result, it is suggested that low-lying excitations at low temperatures are dominated by quasiparticle excitations in the AF ordered state in CePd2Si2 and CeRhzSi,.