MAGNETIC EXCITATIONS IN MODULATED PRNI2SI2

The magnetic excitations in a single crystal of PrNi2Si2 have been stu died by inelastic neutron scattering. Dispersion curves have been foll owed through the centered tetragonal Brillouin zone. In the paramagnet ic phase, at 30 K, the lowest energy magnetic branch exhibits strong d ispersion ranging from 1.9 to 3.5 meV, the minimum energy occurring at the wave vector of the ordered phase; from the observed dispersion th e inter-ionic isotropic bilinear exchange parameters are deduced. At 4 .2 K, in the modulated phase, the same branch presents slightly larger , but not significantly different, dispersion.