Anomalous Thermal Expansion in Substituted Nd₂Fe₁₇₋ₓSiₓ and Nd₂Fe₁₇₋ₓAlₓ Compounds
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 = 0,1,2,3, using high-temperature x-ray diffraction. All compounds crystallize in the rhombohedral Th2Zn17-type structure (space group R3-m). 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.
X. D. Zhang et al., "Anomalous Thermal Expansion in Substituted Nd₂Fe₁₇₋ₓSiₓ and Nd₂Fe₁₇₋ₓAlₓ Compounds," IEEE Transactions on Magnetics, Institute of Electrical and Electronics Engineers (IEEE), Jan 1995.
The definitive version is available at http://dx.doi.org/10.1109/20.489602
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