NEUTRON-SCATTERING STUDY OF ANTIFERROMAGNETIC CORRELATIONS IN THE KONDO SEMICONDUCTOR CENISN

Spin excitations in the Kondo semiconductor CeNiSn have been studied i n a wide Q-range and in the energy range of ($) over bar h omega = 1.2 -7 meV by means of single-crystal neutron scattering. The magnetic flu ctuation at low temperatures in this energy range is dominated by the easy a-axis component Im chi(aa). Below the coherence temperature of 2 0 K, two dynamic antiferromagnetic correlations develop as excitation peaks at ($) over bar h omega = 2 and 4 meV. The 4 meV excitation appe ars at Q = (Q(a), 1/2 + n, Q(c)) where Q(a) and Q(c) are arbitrary and n is an integer, which indicates that the correlation is quasi-one di mensional along the b-axis. The 2 meV excitation appears around Q = (0 , 0, 1) and (0, 1, 0), which shows three-dimensional Q-dependence. The se two excitations reflect the nature of the Kondo coherent state of C eNiSn.