Abstract
A structural and magnetic characterization of the compounds R 2 Fe 17 H x through the R series (except for R = Eu, Yb) is presented. The starting alloys crystallize with the rhombohedral ( Th 2 Zn 17- type R-3 m) or the hexagonal ( Th 2 Ni 17- type P6 3/ mmc) structure for the light and heavy rare earths, respectively. It is seen that the host alloy symmetry is retained upon hydrogenation. Hydrogen is found to accomodate rare earth-rich octahedral and tetrahedral sites. The maximum hydrogen uptake ranges from 3 to 5 hydrogen atoms per formula unit for the heavier and lighter rare earths, respectively. The highly anisotropic cell expansion upon hydrogenation is analyzed. A filling scheme for hydrogen is proposed. The effect of hydrogenation on intrinsic magnetic parameters such as T C and the total magnetization has been studied. It is correlated to the variation of short Fe-Fe distances within the structure and discussed in terms of variations of the exchange interaction. It is also shown that hydrogenation modifies the thermal variation of the anisotropy constants in some compounds.
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