Interplay of magnetic and hydrogen orders in the laves hydride YMn2H4.3

We have performed a neutron-diffraction study of the Laves hydride YMn2H4.3 to investigate the interplay between the atomic order in the hydrogen sublattice and the magnetic structure. We find that structural order in the H sublattice and antiferromagnetic order in the Mn sublattice have the same rhombohedral symmetry. At ambient pressure we observe a first-order magnetostructural transition, where the magnetic sublattice transforms from a paramagnetic state to an antiferromagnetic one, as the hydrogen atoms form the ordered superstructure. An applied pressure decouples the two types of order, which then occur at different temperatures. It allows us to separate the effects of structural order from those related to the average Mn-Mn distance. copyright 1997 The American Physical Society