Abstract

Curie temperatures ( T c) of Fe-rich rare-earth compounds are very sensitive to the changes in the hybridization. This is responsible for the well-known large increase in T c of 2–17 compounds with interstitial and substitutional modifications. The Nd 5Fe 17 compound has attracted some attention recently as a possible permanent-magnet material. Hydrogenation of this compound (Nd 5Fe 17H 16) produces 14.4% volume expansion and increases its T c and magnetization by 14% and 20%, respectively. Because of the large number of atom per unit cell in this crystal (264 atoms) and the lack of information on the positions of hydrogen atoms, we perform first-principle electronic structure calculations for different volumes to study the effect of interstitial impurities such as H on the magnetic properties of Nd 5Fe 17 This is a resonable procedure because the primariy effect of minimally hybridizing impurity such as H is the magnetovolume effect. Because of the similar close-packed environment in Fe-rich compounds and fcc iron these calculations are repeated for fcc iron and the varition of T c with the average Wigner–Seitz radius is quite similar for the two systems giving a universal curve for Fe-rich compounds. The calculated results are also in good agreement with the experimental data for Nd 5Fe 17H 16.

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