CRYSTAL-FIELD AND COMPLEX PHASE-DIAGRAM IN HEXAGONAL PRGA2

A determination of the crystal field has been made in the hexagonal co mpound PrGa2 starting from a careful joint analysis of specific heat, magnetic susceptibility and inelastic neutron scattering experiments. The ground state consists of one singlet and one doublet very close to each other, which explains the existence of a collinear long period-a ntiphase magnetic structure at low temperature. From these crystal fie ld parameters, a quantitative analysis of the complex magnetic propert ies of the ordered phase has been performed by using a self-consistent periodic-field model. In particular, evidence of a field transition t owards a fan magnetic structure within the basal plane has been found during the magnetization process along the 120! axis at 5 K. Moreover , as expected, the specific heat variation is strongly affected by the modulated character of the magnetic arrangement below T(N) = 7.2 K.