Influence of H/D isotopic substitution on the first-order magnetic transition in YFe2(D1-xHx)4.2 compounds (x=0, 0.64, 1)

The structural and magnetic properties of YFe2D4.2 powders are studied by X-ray and neutron powder diffraction, high magnetic field magnetization measurements, and Fe-57 Mossbauer spectroscopy. At 290 K the compound is monoclinic. Transformations from monoclinic to hexagonal (cubic with rhombohedral distortion), and then from hexagonal to cubic symmetry are observed over a short temperature range (320-343 K). They are related to a deuterium order-disorder transition associated with a small increase in magnetization. A metamagnetic transition is observed at 90 K accompanied by a 0.5% cell-volume decrease. In order to solve its magnetic structure, YFe2(D0.36H0.64)(4.2) has been studied by neutron diffraction. A lowering of the Fe moment amplitude and its rotation around the monoclinic b(m)-axis are found. A large isotopic effect is also observed since the magnetization jump is shifted from 90 K for x = 0, to 120 K for x = 0.64; and to 140 K for x = 1. (C) 2004 Elsevier B.V. All rights reserved.