PARAMAGNETIC EXCITATIONS IN SINGLET GROUND-STATE PRNI2SI2

The dispersion curves for magnetic excitations along the principal dir ections of the Brillouin zone of the singlet ground state compound PrN i2Si2 have been measured at 30 K by inelastic neutron-scattering exper iments in the paramagnetic phase. From these data we have extracted in formation about the main exchange interaction coupling parameters J(ij ) that are responsible for the appearance of an amplitude modulated ma gnetic order in this compound below T-N=20 K. The results are consiste nt with the long-range character of Ruderman-Kittel-Kasuya-Yosida inte ractions because in order to describe the dispersion curves observed a t 30 K it is necessary to consider the influence of the interaction to the eighth nearest-neighbor Pr3+ ion along the c direction. In additi on, we have studied the thermal dependence of the excitations at sever al representative points in the Brillouin zone that show an important softening as the temperature is lowered to T-N. [S0163-1829(97)03042-7 ].