AL NUCLEAR-QUADRUPOLE-RESONANCE STUDIES OF CEAL2

We report Al-27 nuclear-quadrupole-resonance (NQR) studies on CeAl2 in the temperature range between 0.09 and 4.2 K. Below T(N)=3.45 K CeAl2 orders antiferromagnetically. The spin-lattice relaxation rate (T1(-1)) shows a sharp peak at T(N), and the NQR linewidth increases from 27+/-3 kHz in the paramagnetic state to 270+/-15 kHz at 2 K. Below 1.5 K, in the low-temperature regime of the magnetically ordered state, the temperature dependence of the spin-lattice relaxation rate follows a Korringa law with (T1T)-1=7.9+/-0.8 (K sec)-1. This relaxation rate is much larger than those found in normal metals. Above 1.5 K deviations from the Korringa law are observed. These deviations are consistent with a relaxation produced by magnonlike excitations with an energy gap of 11+/-3 K, in agreement with results of previous neutron scattering and T1 measurements in the temperature ran above 1.5 K.