Critical Behavior of Thermal Expansion and Magnetostriction in the Vicinity of the First order transition at the Curie Point of Gd5(SixGe1-x)4

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Thermal expansion (TE) and magnetostriction (MS) measurements have been conducted for Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} with a series of x values to study its critical behavior in the vicinity of transition temperatures. It was found that the Curie temperature of Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} for x 0 {approx} 0.5 is dependent on magnetic field, direction of change of temperature (Tc on cooling was lower than Tc on heating), purity of Gd starting material, compositions, material preparation methods, and also can be triggered by the external magnetic field with a different dT/dB rate for different x values. For Gd{sub ... continued below

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Han, Mangui December 19, 2004.

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  • Ames Laboratory
    Publisher Info: Ames Lab., Ames, IA (United States)
    Place of Publication: Ames, Iowa

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Thermal expansion (TE) and magnetostriction (MS) measurements have been conducted for Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} with a series of x values to study its critical behavior in the vicinity of transition temperatures. It was found that the Curie temperature of Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} for x 0 {approx} 0.5 is dependent on magnetic field, direction of change of temperature (Tc on cooling was lower than Tc on heating), purity of Gd starting material, compositions, material preparation methods, and also can be triggered by the external magnetic field with a different dT/dB rate for different x values. For Gd{sub 5}(Si{sub 1.95}Ge{sub 2.05}), Gd{sub 5}(Si{sub 2}Ge{sub 2}), Gd{sub 5}(Si{sub 2.09}Ge{sub 1.91}), it was also found that the transition is a first order magneto-structural transition, which means the magnetic transition and crystalline structure transition occur simultaneously, and completely reversible. Temperature hysteresis and phase coexistence have been found to confirm that it is a first order transformation. While for Gd{sub 5}(Si{sub 0.15}Ge{sub 3.85}), it is partially reversible at some temperature range between the antiferromagnetic and the ferromagnetic state. For Gd{sub 5}(Si{sub 2.3}Ge{sub 1.7}) and Gd{sub 5}(Si{sub 3}Ge{sub 1}), it was a second order transformation between the paramagnetic and ferromagnetic state, because no {Delta}T have been found. Giant magnetostriction was only found on Gd{sub 5}(Si{sub 1.95}Ge{sub 2.05}), Gd{sub 5}(Si{sub 2}Ge{sub 2}), Gd{sub 5}(Si{sub 2.09}Ge{sub 1.91}) in their vicinity of first order transformation. MFM images have also been taken on polycrystal sample Gd{sub 5}(Si{sub 2.09}Ge{sub 1.91}) to investigate the transformation process. The results also indicates that the Curie temperature was lower and the thermally-induced strain higher in the sample made from lower purity level Gd starting materials compared with the sample made from high purity Gd metal. TE, MS, MFM and VSM measurements on single crystal Gd{sub 5}(Si{sub 2}Ge{sub 2}) and Gd{sub 5}(Si{sub 2.3}Ge{sub 1.7}) samples have shown their strong anisotropic behaviors.

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4578 Kilobytes pages

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OSTI as DE00837267

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  • Other Information: TH: Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US)

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  • Report No.: IS-T 2309
  • Grant Number: W-7405-Eng-82
  • Office of Scientific & Technical Information Report Number: 837267
  • Archival Resource Key: ark:/67531/metadc781141

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  • December 19, 2004

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  • Dec. 3, 2015, 9:30 a.m.

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  • June 10, 2016, 6:20 p.m.

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Han, Mangui. Critical Behavior of Thermal Expansion and Magnetostriction in the Vicinity of the First order transition at the Curie Point of Gd5(SixGe1-x)4, thesis or dissertation, December 19, 2004; Ames, Iowa. (digital.library.unt.edu/ark:/67531/metadc781141/: accessed June 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.