Time-resolved synchrotron x-ray diffraction studies of the crystallization of amorphous Co_(80-x)Fe_xB₂₀

Journal Article · Sun Sep 28 04:00:00 EDT 2014 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4896367· OSTI ID:22305699

Greig, D. ^[1]; Lucas, C. A. ^[2]; Kilcoyne, S. H. ^[3]

---

1. School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)
2. Oliver Lodge Laboratory, Department of Physics, University of Liverpool, Liverpool L69 7ZE (United Kingdom)
3. School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH (United Kingdom)

This paper addresses the time-dependent crystallization process occurring in “bulk” amorphous Co_(80-x)Fe_xB₂₀ (x = 20, 40) metallic ribbons by means of synchrotron x-ray diffraction (SXRD) and transmission electron microscopy. Metallic ribbons, produced via melt-spinning technique, were annealed in-situ, with SXRD patterns collected every 60 s. SXRD reveals that Co₄₀Fe₄₀B₂₀ alloys crystallize from an amorphous structure to a primary bcc α-(Co,Fe) phase, whereas Co₆₀Fe₂₀B₂₀ initially crystallizes into the same bcc α-(Co,Fe) but exhibits cooperative growth of both stable and metastable boride phases later into the hold. Johnson-Mehl-Avrami-Kolmogorov statistics was used on post annealed samples to determine the mechanisms of growth and the activation energy (E_a) of the α-(Co,Fe) phase. Results indicate that the growth mechanisms are similar for both alloy compositions for all annealing temperatures, with the Avrami exponent of n = 1.51(1) and 2.02(6) for x = 20 and 40, respectively, suggesting one-dimensional growth, with a decreasing nucleation rate. Activation energy for α-(Co,Fe) was determined to be 2.7(1) eV and 2.4(3) eV in x = 20 and 40, respectively, suggesting that those alloys with a lower Co content have a stronger resistance to crystallization. Based on these results, fabrication of CoFeB magnetic tunnel junctions via depositing amorphous layers and subsequently annealing to induce lattice matching presents itself as a viable and efficient method, for increasing the giant magnetoresistance in magnetic tunnel junctions.

• OSTI ID: 22305699
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 12 Vol. 116; ISSN JAPIAU; ISSN 0021-8979
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACTIVATION ENERGY
ALLOYS
ANNEALING
BCC LATTICES
BORON COMPOUNDS
COBALT COMPOUNDS
CRYSTALLIZATION
FABRICATION
IRON COMPOUNDS
LAYERS
MAGNETORESISTANCE
SYNCHROTRON RADIATION
TIME DEPENDENCE
TIME RESOLUTION
TRANSMISSION ELECTRON MICROSCOPY
TUNNEL EFFECT
X-RAY DIFFRACTION