Al nuclear-quadrupole-resonance studies ofCeAl2

We report ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ nuclear-quadrupole-resonance (NQR) studies on ${\mathrm{CeAl}}_2$ in the temperature range between 0.09 and 4.2 K. Below ${\mathit{T}}_{\mathit{N}}$=3.45 K ${\mathrm{CeAl}}_2$ orders antiferromagnetically. The spin-lattice relaxation rate (${\mathit{T}}_1^{\mathrm{-}1}$) shows a sharp peak at ${\mathit{T}}_{\mathit{N}}$, 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 (${\mathit{T}}_1$T${)}^{\mathrm{-}1}$=7.9±0.8 (K sec${)}^{\mathrm{-}1}$. 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 ${\mathit{T}}_1$ measurements in the temperature range above 1.5 K.