Soft-mode-driven magnetic ordering in the singlet ground-state system PrNi

Abstract

Measurements of the dispersion of the low-energy magnetic modes have been performed by the inelastic neutron scattering technique for the singlet ground state system PrNi above the Curie temperature (Tc=20.5 K). The neutron spectra were collected in the energy-transfer range up to 7 meV. Two well-defined excitons were observed in PrNi along the crystallographic directions [100] and [001]. A progressive softening of the magnetic mode along the [100] direction in the paramagnetic phase at temperatures approaching Tc has been observed at the magnetic Bragg point (zone center) in PrNi. The temperature dependence and the character of the dispersion of the magnetic excitations in PrNi are indicative of the soft-mode-driven mechanism of the magnetic ordering in this compound.