Pressure-induced decoupling of the magnetic ordering of the Mn and Gd sublattices in GdMn2

The thermal expansion of GdMn2 was measured under pressures up to 20 kbar. The large positive magnetovolume effect, caused by the onset of the Mn magnetism, is found to be shifted towards lower temperatures with pressure, and vanishes around 15 kbar. Above this pressure only the Gd sublattice shows long-range magnetic order. Between 6 and 15 kbar the Gd and Mn sublattices order separately. The pressure-induced splitting of the ordering temperatures is ascribed to the Mn magnetism instability, which is observed for certain RMn2 compounds. (author)