Structural and Magnetothermal Properties of Compounds: Yb₅Si_xGe_4-x,Sm₅Si_xGe_4-x, EuO, and Eu₃O₄

Thesis/Dissertation · Mon Jan 01 00:00:00 EST 2007

DOI:https://doi.org/10.2172/909489· OSTI ID:909489

Ahn, Kyunghan ^[1]

---

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

The family of R₅Si_xGe_4-x alloys demonstrates a variety of unique physical phenomena related to magneto-structural transitions associated with reversible breaking and reforming of specific bonds that can be controlled by numerous external parameters such as chemical composition, magnetic field, temperature, and pressure. Therefore, R₅Si_xGe_4-x systems have been extensively studied to uncover the mechanism of the extraordinary magneto-responsive properties including the giant magnetoresistance (GMR) and colossal magnetostriction, as well as giant magnetocaloric effect (GMCE). Until now, more than a half of possible R₅Si_xGe_4-x pseudobinary systems have been completely or partially investigated with respect to their crystallography and phase relationships (R = La, Pr, Nd, Gd, Tb, Dy, Er, Lu, Y). Still, there are other R₅Si_xGe_4-x systems (R = Ce, Sm, Ho, Tm, and Yb) that are not studied yet. Here, we report on phase relationships and structural, magnetic, and thermodynamic properties in the Yb₅Si_xGe_4-xand Sm₅Si_xGe_4-x pseudobinary systems, which may exhibit mixed valence states. The crystallography, phase relationships, and physical properties of Yb₅Si_xGe_4-x alloys with 0 ≤ x ≤ 4 have been examined by using single crystal and powder x-ray diffraction at room temperature, and dc magnetization and heat capacity measurements between 1.8 K and 400 K in magnetic fields ranging from 0 to 7 T. Unlike the majority of R₅Si_xGe_4-x systems studied to date, where R is the rare earth metal, all Yb-based germanide-silicides with the 5:4 stoichiometry crystallize in the same Gd₅Si₄-type structure. The magnetic properties of Yb₅Si_xGe_4-x materials are nearly composition-independent, reflecting the persistence of the same crystal structure over the whole range of x from 0 to 4. Both the crystallographic and magnetic property data indicate that Yb₅Si_xGe_4-x alloys are mixed valence systems, in which the majority (60%) of Yb atoms is divalent, while the minority (40%) is trivalent. This finding is supported by recent Moessbauer spectroscopy data.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC02-07CH11358
• OSTI ID: 909489
• Report Number(s): IS-T 2437; TRN: US200722%%1278
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALLOYS
ATOMS
CHEMICAL COMPOSITION
CRYSTAL STRUCTURE
CRYSTALLOGRAPHY
MAGNETIC FIELDS
MAGNETIC PROPERTIES
MAGNETIZATION
MAGNETORESISTANCE
MAGNETOSTRICTION
MOESSBAUER EFFECT
MONOCRYSTALS
PHYSICAL PROPERTIES
RARE EARTHS
SPECIFIC HEAT
STOICHIOMETRY
THERMODYNAMIC PROPERTIES
VALENCE
X-RAY DIFFRACTION