Ferroquadrupolar ordering in PrTi2Al20

Abstract

The origin of the nonmagnetic phase transition in PrTi${}_{2}$Al${}_{20}$, reported earlier in a macroscopic study, has been asserted microscopically using elastic and inelastic neutron scattering techniques. It has been shown spectroscopically that the crystalline-electric-field ground state is a nonmagnetic ${\ensuremath{\Gamma}}_{3}$ doublet, whereas the excited states are two triplets (${\ensuremath{\Gamma}}_{4}$ and ${\ensuremath{\Gamma}}_{5}$) and a singlet (${\ensuremath{\Gamma}}_{1}$). The diffraction experiment under external magnetic field shows that the nonmagnetic transition is indeed ferroquadrupolar ordering, which takes place as a consequence of cooperative removal of the ground-state-doublet degeneracy. It is therefore concluded that PrTi${}_{2}$Al${}_{20}$ is another rare example of Pr compounds exhibiting nonmagnetic quadrupolar order.