MAGNETIC-PROPERTIES AND AL-27 PULSED NUCLEAR-MAGNETIC-RESONANCE MEASUREMENTS OF RAL(2) (R=LU, CE, GD)

The magnetic properties and the electronic structures of RAl(2) (R = Lu, Ce, Gd) are investigated by magnetic susceptibility measurements and Al-27 pulsed nuclear magnetic resonance (NMR) spectroscopy. The magnetic susceptibility of LuAl2 is weakly temperature dependent and shows a Pauli susceptibility of 10.1 x 10(-5) emu/mol, which means 3.2 states/eV/formula unit. On the other hand, the susceptibility data of CeAl2 and GdAl2 show the Curie-Weiss behavior for paramagnets. The susceptibility data at low temperature confirm that CeAl2 undergoes an antiferromagnetic phase transition near 4 K whereas GdAl2 undergoes a ferromagnetic transition at 170 K. The Al-27 NMR Knight shift of LuAl2 is temperature independent around -0.04%. The Knight shifts of CeAl2 and GdAl2 are strongly temperature dependent and proportional to the susceptibility, which suggests that the Knight shifts are dominated by the core polarization of the 4f orbitals. The hyperfine coupling constants ale estimated to be +5.7 kOe/mu(B) for CeAl2 and -18 kOe/mu(B) for GdAl2. The spin-lattice relaxation rate 1/T-1 for LuAl2 shows a Korringa behavior as observed for most nonmagnetic metals. The relaxation rates and the Knight shifts give 1.09 of the Korringa ratio. The relaxation rates for CeAl2 and GdAl2 are very high and strongly temperature dependent. This temperature dependence originates from the thermal excitation of 4f spin fluctuations.