NEUTRON DIFFRACTION STUDY OF MAGNETIC STRUCTURES AND PHASE TRANSITIONS AT VERY HIGH PRESSURES I. N. Goncharenko, Russian Research Center "Kurchatov Institute", 123182 Moscow, Russia Leon Brillouin Laboratory, CEA-CNRS, CEN Saclay, 91191 Gif-sur-Yvette, France

High-intensity low-background neutron diffraction and high-pressure anvil technique have been used in the studies of magnetic ordering up to the pressures of 10 GPa (sapphire anvils) and 25 GPa (diamond anvils) [1]. The experiments have been performed both for powders and single crystals in the wide temperature range 1.5-300 K.

With the above technique, various magnetic materials have been studied, including hydrides, pnictides and chalcogenides of transition metals, lanthanides and actinides. A special interest was devoted to cases, where a high sensitivity of magnetic properties to the interatomic distances makes high pressure experiments as a powerful tool for studies of the magnetic interactions. Such a situation has been observed in uranium monopnictides, where a mixing of electronic states leads to a complicated magnetic pressure - temperature phase diagram. General traits for a transformation of a magnetic structure due to the pressure induced crystal structure transition NaCl-CsCl have been studied in europium monochalcogenides.

Future prospects of magnetic neutron studies are represented, including a combination of high magnetic fields and high pressures in neutron experiments, development of a specialized neutron diffractometer for high pressure studies.

[1] I. N. Goncharenko, J. - M.Mignot, G. Andre, O. A. Lavrova, I. Mirebeau, V. A. Somenkov, High Pressure Research, 14(1995), 41-53.