Amorphous-to-crystalline transition in Tb 33 Fe 66 films studied via EXAFS
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Introduction:
In this paper we present EXAFS studies of amorphous Tb3 3Fe66 films before and after heat treatments at temperatures approaching and exceeding the crystallization temperature. We focus on the qualitative changes in the Fourier transformed Fe EXAFS data and the results of modeling the near neighbor environments using empirical and theoretical standards. A multiple shell model is found to provide the best fit to the local environment around Fe sites. The evolution of structure with heat treatments is found to occur in three distinct stages; relaxation, short-range-ordering, and long-range-ordering. Fits obtained using empirical standards allow the measurement of the fractional amounts of amorphous and bcc crystalline phase after various heat treatments illustrating the progressive crystallization of the sample. Studies investigating the atomic structure have been performed on amorphous R3 3 Fe66 (R: rare earth) alloys; among them Cargil used x-ray scattering to probe Gd33Fe66 [1] and D'Antonio et al. used neutron scattering to probe the structure of Tb 33 Fe 66 and Y 33 Fe66 [2]. Both of these studies report that the local environment of the amorphous R33Fe66 samples bare no resemblance to the local structure of the crystalline Laves phase (RFe2). D'Antonio and coworkers report that the Fe tetrahedral coordination of the Laves phase is preserved in the amorphous analogs while the Tb tetrahedral coordination is not. EXAFS studies of amorphous TbFe films have been performed on TbFe alloys in the compositional range of TbxFel-x, x
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