Critical Behavior of Thermal Expansion and Magnetostriction in the Vicinity of the First order transition at the Curie Point of Gd₅(Si_xGe_1-x)₄

Thesis/Dissertation · Thu Jan 01 00:00:00 EST 2004

DOI:https://doi.org/10.2172/837267· OSTI ID:837267

Han, Mangui ^[1]

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1. Iowa State Univ., Ames, IA (United States)

Thermal expansion (TE) and magnetostriction (MS) measurements have been conducted for Gd₅(Si_xGe_1-x)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 Gd₅(Si_xGe_1-x)₄ for x 0 ~ 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 Gd₅(Si_1.95Ge_2.05), Gd₅(Si₂Ge₂), Gd₅(Si_2.09Ge_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 Gd₅(Si_0.15Ge_3.85), it is partially reversible at some temperature range between the antiferromagnetic and the ferromagnetic state. For Gd₅(Si_2.3Ge_1.7) and Gd₅(Si₃Ge₁), it was a second order transformation between the paramagnetic and ferromagnetic state, because no ΔT have been found. Giant magnetostriction was only found on Gd₅(Si_1.95Ge_2.05), Gd₅(Si₂Ge₂), Gd₅(Si_2.09Ge_1.91) in their vicinity of first order transformation. MFM images have also been taken on polycrystal sample Gd₅(Si_2.09Ge_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 Gd₅(Si₂Ge₂) and Gd₅(Si_2.3Ge_1.7) samples have shown their strong anisotropic behaviors.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: W-7405-Eng-82
• OSTI ID: 837267
• Report Number(s): IS-T 2309; TRN: US200506%%82
• Resource Relation: Other Information: TH: Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); PBD: 19 Dec 2004
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CURIE POINT
HEATING
HYSTERESIS
MAGNETIC FIELDS
MAGNETOSTRICTION
MONOCRYSTALS
POLYCRYSTALS
STRAINS
THERMAL EXPANSION
TRANSFORMATIONS
TRANSITION TEMPERATURE