Neutron-diffraction study of the pressure-temperature phase diagram of EuAs3.

Abstract

Neutron-diffraction investigations have been performed on a single crystal of ${\mathrm{EuAs}}_{3}$ under hydrostatic pressure up to 20 kbar. At pressures up to 2 kbar the magnetic structure is identical to that at ambient pressure. Above P=2 kbar, in addition to the collinear commensurate (AF1) and incommensurate (IC) phases, a helimagnetic phase (HP) develops below 2 K. At about P=3 kbar the commensurate phase is no longer stable and the sine-wave incommensurate phase transforms directly to the helimagnetic phase in which the magnetic moments are modulated in the (010) plane. At P=18 kbar the sine-wave phase itself becomes unstable and the helimagnetic phase develops directly from the paramagnetic phase. There are two triple points in the (P,T) phase diagram of ${\mathrm{EuAs}}_{3}$: one at which the IC, AF1, and HP phases coexist and the other at which the paramagnetic, IC and HP phases coexist. This complicated behavior is quite unexpected for an S-state ion such as ${\mathrm{Eu}}^{2+}$. .AE