Magnetic Neutron Diffraction under Very High Pressures. Study of Europium Monochalcogenides.

We report recent developments on neutron diffraction studies in a wide range of pressures (up to 25 GPa) and temperatures (down to 1. 3 K). The increase of the available pressure range was allowed by technical progresses both in neutron and high pressure instrumentation. As an example, we present a neutron study of the magnetic order in europium monochalcogenides (EuX, X=Se, S, Te) at pressures up to 20. 5 GPa. We observed new magnetic phases in EuTe. These results allow making a direct comparison of the strength of the magnetic exchange in the different member of the family for the same value of the lattice parameter.