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Title: Time-resolved synchrotron x-ray diffraction studies of the crystallization of amorphous Co(80-x)FexB₂₀

This paper addresses the time-dependent crystallization process occurring in “bulk” amorphous Co(80-x)FexB₂₀ (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 (Ea) 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 subsequentlymore » annealing to induce lattice matching presents itself as a viable and efficient method, for increasing the giant magnetoresistance in magnetic tunnel junctions.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Division of Electrical and Electronic Engineering, School of Engineering, Manchester Metropolitan University, Manchester M1 5GD (United Kingdom)
  2. School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)
  3. Oliver Lodge Laboratory, Department of Physics, University of Liverpool, Liverpool L69 7ZE (United Kingdom)
  4. School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH (United Kingdom)
Publication Date:
OSTI Identifier:
22305699
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 12; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
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