Anomalous thermal expansion in substituted Nd/sub 2/Fe/sub 17-x/Si/sub x/ and Nd/sub 2/Fe/sub 17-x/Al/sub x/ compounds

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IEEE Transactions on Magnetics, ISSN: 0018-9464, Vol: 31, Issue: 6, Page: 3662-3664

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Zhang, X. D.; Shumsky, Mark G.; James, William Joseph; Yelon, William B.
Institute of Electrical and Electronics Engineers (IEEE)
Materials Science; Engineering; Chemistry; Physics
article description
the temperature dependencies of the lattice parameters were measured from room temperature to 400°C for powders of the substituted compounds Nd2Fe17-xAlx and Nd2Fe17-xSix, x=0,l,2,3, using high-temperature x-ray diffraction. All compounds crystallize in the rhombohedral Th2Zn17-type structure (space group R3m). Invar-type anomalies are found in the temperature dependence of a and c below the Curie temperatures, Tc, but featuring different substitution effects of Fe by Al and Si atoms, respectively. The Nd2Fe17-xAlx and Nd2Fe17-xSix compounds retain easy-plane anisotropies upon substitution up to x=3. Therefore, the observed spontaneous volume magnetostrictions are due mainly to the isotropic exchange contribution of the iron sublattice. According to the localized model of exchange interactions in R-Fe compounds, the different substitution effects can be ascribed to the different preferential occupation tendencies of Al and Si atoms on the sites of the Th2Zn17-type structure. © 1995 IEEE