Metastable phase formation and magnetic properties of the Fe-Nb system studied by atomistic modeling and ion beam mixing

Journal Article · Tue Jul 01 00:00:00 EDT 2008 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.2955716· OSTI ID:21137393

Tai, K P; Dai, Y; Liu, B X ^[1]

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1. Advanced Materials Laboratory, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China)

With the aid of ab initio calculations, an n-body Fe-Nb embedded-atom potential is first constructed and then applied to study the crystal-to-amorphous phase transition through molecular dynamic simulations. The simulations determine that the glass-forming range of the Fe-Nb system is 18-83 at. % of Nb. In ion beam mixing experiments, five Fe-Nb multilayered films with overall compositions of Fe{sub 85}Nb{sub 15}, Fe{sub 75}Nb{sub 25}, Fe{sub 55}Nb{sub 45}, Fe{sub 25}Nb{sub 75}, and Fe{sub 15}Nb{sub 85}, respectively, are irradiated by 200 keV xenon ions to doses in the range of (1-7)x10{sup 15}Xe{sup +}/cm{sup 2}. The result shows that the Fe-Nb metallic glasses can be synthesized within a composition range of 25-75 at. % of Nb, matching reasonably well the theoretical prediction. Moreover, in the Fe{sub 55}Nb{sub 45} sample, a fcc-structured alloy phase with a large lattice constant of a{approx_equal}0.408 nm was obtained at a dose of 3x10{sup 15} Xe{sup +}/cm{sup 2} and the associated magnetic moment per Fe atom was measured to be 2.41{mu}{sub B}. The observed magnetic moment is much greater than the initial value of 1.42{mu}{sub B} in the bcc-Fe lattice and can thus serve as evidence confirming the high-spin ferromagnetic state of fcc Fe predicted by ab initio calculations. Interestingly, further irradiation induced phase separation in the Fe{sub 55}Nb{sub 45} sample, i.e., irradiation to a dose of 5x10{sup 15} Xe{sup +}/cm{sup 2} results in the growth of a fractal pattern consisting of Fe{sub 72}Nb{sub 28} nanoclusters embedded in Fe{sub 35}Nb{sub 65} matrix. The formation mechanism of the metastable phases as well as that of the fractal pattern observed in the Fe-Nb system was discussed in terms of the atomic collision theory and the well-known cluster-diffusion-limited-aggregation model.

• OSTI ID: 21137393
• Journal Information: Journal of Applied Physics, Vol. 104, Issue 1; Other Information: DOI: 10.1063/1.2955716; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AMORPHOUS STATE
ATOM COLLISIONS
BCC LATTICES
BINARY ALLOY SYSTEMS
CRYSTAL GROWTH
FCC LATTICES
FERROMAGNETIC MATERIALS
ION BEAMS
IRON ALLOYS
KEV RANGE 100-1000
LATTICE PARAMETERS
MAGNETIC MOMENTS
MAGNETIC PROPERTIES
METALLIC GLASSES
METASTABLE STATES
MOLECULAR DYNAMICS METHOD
NANOSTRUCTURES
NIOBIUM ALLOYS
SIMULATION
XENON IONS