PRESSURE-INDUCED DECOUPLING OF THE MAGNETIC-ORDERING OF THE MN AND GDSUBLATTICES IN GDMN2

The thermal expansion of GdMn2 was measured under pressures up to 20 k bar. The large positive magnetovolume effect, caused by the onset of t he Mn magnetism, is found to be shifted towards lower temperatures wit h pressure, and vanishes around 15 kbar. Above this pressure only the Gd sublattice shows long-range magnetic order. Between 6 and 15 kbar t he Gd and Mn sublattices order separately. The pressure-induced splitt ing of the ordering temperatures is ascribed to the Mn magnetism insta bility, which is observed for certain RMn(2) compounds.