Synchrotron Diffraction Studies of Spontaneous Magnetostriction in Rare Earth Transition Metal Compounds

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Thermal expansion anomalies of R{sub 2}Fe{sub 14}B and R{sub 2}Fe{sub 17}C{sub x} (x = 0,2) (R = Y, Nd, Gd, Tb, Er) stoichiometric compounds are studied with high-energy synchrotron X-ray powder diffraction using Debye-Schemer geometry in temperature range 10K to 1000K. Large spontaneous magnetostriction up to their Curie temperatures (T{sub c}) is observed. The a-axes show relatively larger invar effects than c-axes in the R{sub 2}Fe{sub 14}B compounds whereas the R{sub 2}Fe{sub 17}C{sub x} show the contrary anisotropies. The iron sub-lattice is shown to dominate the spontaneous magnetostriction of the compounds. The contribution of the rare earth sublattice is roughly ... continued below

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Yang, Ning December 19, 2004.

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Thermal expansion anomalies of R{sub 2}Fe{sub 14}B and R{sub 2}Fe{sub 17}C{sub x} (x = 0,2) (R = Y, Nd, Gd, Tb, Er) stoichiometric compounds are studied with high-energy synchrotron X-ray powder diffraction using Debye-Schemer geometry in temperature range 10K to 1000K. Large spontaneous magnetostriction up to their Curie temperatures (T{sub c}) is observed. The a-axes show relatively larger invar effects than c-axes in the R{sub 2}Fe{sub 14}B compounds whereas the R{sub 2}Fe{sub 17}C{sub x} show the contrary anisotropies. The iron sub-lattice is shown to dominate the spontaneous magnetostriction of the compounds. The contribution of the rare earth sublattice is roughly proportional to the spin magnetic moment of the rare earth in the R{sub 2}Fe{sub 14}B compounds but in R{sub 2}Fe{sub 17}C{sub x}, the rare earth sub-lattice contribution appears more likely to be dominated by the local bonding. The calculation of spontaneous magnetostrain of bonds shows that the bonds associated with Fe(j2) sites in R{sub 2}Fe{sub 14}B and the dumbbell sites in R{sub 2}Fe{sub 17}C{sub x} have larger values, which is strongly related to their largest magnetic moment and Wigner-Seitz atomic cell volume. The roles of the carbon atoms in increasing the Curie temperatures of the R{sub 2}Fe{sub 17} compounds are attributed to the increased separation of Fe hexagons. The R{sub 2}Fe{sub 17} and R{sub 2}Fe{sub 14}B phases with magnetic rare earth ions also show anisotropies of thermal expansion above T{sub c}. For R{sub 2}Fe{sub 17} and R{sub 2}Fe{sub 14}B the a{sub a}/a{sub c} > 1 whereas the anisotropy is reversed with the interstitial carbon in R{sub 2}Fe{sub 17}. The average bond magnetostrain is shown to be a possible predictor of the magnetic moment of Fe sites in the compounds. Both of the theoretical and phenomenological models on spontaneous magnetostriction are discussed and a Landau model on the spontaneous magnetostriction is proposed.

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2977 Kilobytes pages

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INIS; OSTI as DE00835381

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  • Other Information: PBD: 19 Dec 2004

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  • Report No.: IS-T 1993
  • Grant Number: W-7405-Eng-82
  • Office of Scientific & Technical Information Report Number: 835381
  • Archival Resource Key: ark:/67531/metadc784954

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  • December 19, 2004

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  • Dec. 3, 2015, 9:30 a.m.

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  • Jan. 9, 2018, 9:53 a.m.

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Yang, Ning. Synchrotron Diffraction Studies of Spontaneous Magnetostriction in Rare Earth Transition Metal Compounds, thesis or dissertation, December 19, 2004; Ames, Iowa. (digital.library.unt.edu/ark:/67531/metadc784954/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.