Magnetostriction, elasticity, and D03 phase stability in Fe–Ga and Fe–Ga–Ge alloys
Abstract
The contrast between the saturation tetragonal magnetostriction, λγ,2 = (3/2)λ100, of Fe1−xGax and Fe1−yGey, at compositions where both alloys exhibit D03 cubic symmetry (second peak region), was investigated. This region corresponds to x = 28 at. % Ga and y = 18 at. % Ge or, in terms of e/a = 2 x + 3 y + 1, to an e/a value of ∼1.55 for each of the alloys. Single crystal, slow-cooled, ternary Fe1−x−y GaxGey alloys with e/a ∼1.55 and gradually increasing y/x were investigated experimentally (magnetostriction, elasticity, powder XRD) and theoretically (density functional calculations). It was found that a small amount of Ge (y = 1.3) replacing Ga in the Fe–Ga alloy has a profound effect on the measured λγ,2. As y increases, the drop in λγ,2 is considerable, reaching negative values at y/x = 0.47. The two shear elastic constants c′ = (c11− c12)/2 and c44 measured for four compositions with 0.06 ≤ y/x ≤ 0.45 at 7 K range from 16 to 21 GPa and from 133 to 138 GPa, respectively. Large temperature dependence was observed for c′ but not for c44, a trend seen in other high-solute Fe alloys. The XRD analysis shows that the metastable D03 structure, observed previously in slow-cooled Fe–Ga at e/a = 1.55, is replaced with two phases, fcc L12 and hexagonal D019, at just 1.6 at. % Ge. The two are the stable phases of the assessed Fe–Ga phase diagram at x ∼ 28. Notably, at y = 7.8, only the D03 phase (the equilibrium phase of Fe–Ge at e/a = 1.54) was found in the ternary alloy. The theory also shows that the D03 instability is removed for compositions with y ≥ 3.9, when D03 becomes the structure’s ground-state phase. Thus, the high, positive λγ,2 value for Fe–Ga at x = 28 could be the result of the high sensitivity of its metastable D03 structure.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Mar 18, 2011
- Source ID
- 10.1063/1.3535444
Entities
People
- A. E. Clark
- Gabriela Petculescu
- J. B. Restorff
- K. B. Hathaway
- K. L. Ledet
- M. Wun-fogle
- Mingxiong Huang
- R. Q. Wu
- T. A. Lograsso
- Y. N. Zhang
Organizations
- Ames National Laboratory
- Naval Surface Warfare Center
- Office of Naval Research
- University of California
- University of Louisiana at Lafayette