Ga-NMR study of the low-energy excitations in

We report the results of ⁶⁹Ga- and ⁷¹Ga-NMR measurements on NdGa₂ at temperatures between 0.1 and and in applied magnetic fields between zero and 74 kOe. NdGa₂ orders antiferromagnetically below and undergoes several metamagnetic transitions in external magnetic fields. In zero applied magnetic field and below the temperature dependence of the spin-lattice relaxation rate T1 ^-1 ( T ) shows a large linear-in-T term, about two orders of magnitude higher than for the reference compound LaGa₂. This strong enhancement confirms the presence of low-energy excitations in the antiferromagnetic phase of NdGa₂ as was previously indicated by specific heat data. Above , T1 ^-1 ( T ) is dominated by an exponential term, which we associate with excitations between the lowest energy levels of the f-electron system. The separation of these energy levels is determined by exchange, crystal-field and Zeeman interactions. Received 3 September 1998 and Received in final form 3 November 1998