Evidence for new crystalline phases formed during early stages of crystallization of amorphous FeCuNbSiB alloys

Basheed, G. A. ; Sarkar, S. ; Kaul, S. N. (2006) Evidence for new crystalline phases formed during early stages of crystallization of amorphous FeCuNbSiB alloys Journal of Physics: Condensed Matter, 18 (29). pp. 6607-6620. ISSN 0953-8984

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Official URL: http://iopscience.iop.org/0953-8984/18/29/004

Related URL: http://dx.doi.org/10.1088/0953-8984/18/29/004

Abstract

Amorphous FeCuNbSiB alloys with composition near Fe73.5Cu1Nb3Si13.5B9 (the well-studied FINEMET alloy) were annealed at 520 °C for different durations of time, tA, varying from 3 to 20 min. Detailed investigation of the structure and composition of crystalline phases formed during the initial stages of crystallization in these alloys using techniques such as x-ray diffraction, Mossbauer spectroscopy, scanning electron microscopy, atomic force microscopy and energy dispersive absorption of x-rays, revealed the following. New crystalline phases, tetragonal Fe3B and hexagonal Fe2Si, not reported previously, exist in all the nanocrystalline alloys in question in contrast to the well-documented cubic Fe-Si phase with the DO3 structure which coexists with the Fe3B and Fe2Si phases in some compositions only. The crystallization of Fe3B and Fe2Si nanocrystalline grains starts at the surface of the ribbons and then proceeds to the bulk whereas the crystallization of DO3 Fe-Si gets initiated within the bulk. The average size of the nanocrystalline grains of the Fe3B and Fe2Si and cubic DO3 Fe-Si structures in the residual amorphous matrix is around 20 nm but their volume fractions are as low as ≈ 5%, 10%, and 7%, respectively. The cubic Fe-Si nanocrystals of the DO3 structure have a silicon concentration in the range 15-20 at.%. The magnetic moments in the amorphous precursor point, on average, are 40° out of the ribbon plane while in the nanocrystalline alloys this angle varies between 2° and 19° depending on the Fe concentration.

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