NMR in CeAl2: Crystal-field effects and magnetic order in the low-temperature phase

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Abstract
27Al NMR spectra have been observed in polycrystalline CeAl2 for temperatures between 2 and 295 K. Frequency shifts, quadrupole couplings and linewidths have been obtained in the paramagnetic phase above Tc=3.8 K. The isotropic shift K′ i due to Ce3+ spin polarization indicates a marked decrease of the 27Al hyperfine field Hhf=K′ i/χ with increasing temperature. A non‐dipolar contribution to the anisotropic shift scales with the observed K′ i. Both these results can be accounted for only by an anisotropic local moment‐conduction electron coupling. Below Tc the NMR line broadens appreciably, attaining a field‐independent value at very low temperatures. This observation is consistent with the onset of magnetic ordering, although the absence of a large shift and the magnitude of the linewidth are not understood.