On the properties of CeFe2Hx hydrided at low temperatures

Abstract

Abstract The cubic Laves phase compound CeFe 2 could be hydrided down to 203 K and 0.5 atm hydrogen pressure, in a copper reactor allowing fast withdrawal of heat. The hydrides so formed at low temperatures contained an appreciably higher hydrogen concentration, as compared with earlier reported values. Their properties are also significantly different. No crystalline ternary hydride is formed down to 203 K. Simultaneous occupation of various available sites by hydrogen atoms, resulting in a composition CeFe 2 H x ( x ⩾4) of the hydrided fraction, coupled with the inability of iron atoms to diffuse rapidly, is believed to be responsible for the ternary amorphous phase formation. X-ray diffraction, Mossbauer studies with and without magnetic field, a.c. and d.c. magnetic susceptibility and electrical resistance measurements are reported on the hydrides. The amorphous ternary hydride formed at 223 K does not exhibit a simple ferromagnetic ordering, in contradiction to earlier reports, as shown by a broad maximum in a.c. susceptibility at about 250 K. This ordering can, however, be transformed to the normal ferromagnetic type by applying a small magnetic field of a few kilogauss. The temperature dependence of the electrical resistance of the same sample exhibits a semiconducting behaviour and the magnetic transition at about 250 K is also discernible.