Spin excitations in the Kondo semiconductor CeNiSn have been studied in a wide Q-range and in the energy range of h(cross) omega =1.2-7 meV by means of single-crystal neutron scattering. The magnetic fluctuation at low temperatures in this energy range is dominated by the easy a-axis component Im chi ad. Below the coherence temperature of 20 K, two dynamic antiferromagnetic correlations develop as excitation peaks at h(cross) omega =2 and 4 meV. The 4 meV excitation appears at Q=(Qa. 1/2 +n, Qc) where Qc and Qc are arbitrary and n is an integer, which indicates that the correlation is quasi-one dimensional along the b-axis. The 2 meV excitation appears around Q=(0,0,I) and (0,1,0), which shows three-dimensional Q-dependence. These two excitations reflect the nature of the Kondo coherent state of CeNiSn.

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