COMPLEX MAGNETIC PHASE-DIAGRAM IN THE HEXAGONAL DYGA2 COMPOUND

Specific heat and neutron diffraction experiments on polycrystalline samples as well as magnetization measurements on a single crystal of the hexagonal DyGa2 compound are presented. Below T(N) (11 K) three antiferromagnetic phases successively appear: two collinear modulated structures for T(N) > T > T2 = 8.7 K and T2 > T > T1 = 6.1 K, the transition at T2 corresponding to a rotation of 90-degrees of the moments, and a simple antiferromagnetic structure below T1. Whereas susceptibility shows a huge peak at T1 and only a very small anomaly at T2 and T(N), specific heat exhibits the largest anomaly at the rotation temperature. Magnetization process exhibit many transitions in the basal plane which is of easy magnetization and also along the c axis. The resulting complex field-temperature phase diagrams along the a, b and c directions of the orthohexagonal cell were carried out. Finally crystal field parameters were determined from the thermal variations of the paramagnetic susceptibility and entropy.