Unique Features of the Crystallization Kinetics of FeCrBSi Thin Films Obtained by Laser Ablation Deposition
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Unique Features of the Crystallization Kinetics of FeCrBSi Thin Films Obtained by Laser Ablation Deposition M. Sorescu1 and A. Grabias1,2 Duquesne University, Department of Physics, Pittsburgh, PA 15282, U.S.A. 2 Institute of Electronic Materials Technology, Wólczynska 133, 01-919 Warsaw, Poland.
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ABSTRACT Pulsed laser deposition was used to obtain a metallic glass in thin film form using a Fe77Cr2B16Si5 amorphous ribbon as a target. The as-deposited films were annealed under the same conditions as the parent ribbon samples in order to compare their crystallization behaviors. Transmission Mössbauer measurements were performed to determine the crystallization products formed due to annealing of the Fe77Cr2B16Si5 ribbon. Conversion electron Mössbauer spectroscopy was used to obtain structural and magnetic information from the thin films as well as from the surface layers of the ribbons. Our Mössbauer study showed that crystallization behavior of the FeCrBSi thin films differs from both the surface and bulk crystallization of the ribbon. Crystallization occurs at lower annealing temperature for the thin film than for the bulk ribbon. Annealed films also contain iron oxides which are not observed in the crystallized ribbons. A formation of a very thin, protective oxide film at the surface of the ribbon is taken into account to explain the differences in the crystallization behavior of the films and ribbons.
INTRODUCTION It has been recognized recently that amorphous iron-based alloys can be successfully obtained in the form of a thin film by using the pulsed laser deposition (PLD) technique [1-3]. In this study we present the Mössbauer effect results obtained for the as-deposited and annealed FeCrBSi thin films ablated from the amorphous Fe77Cr2B16Si5 ribbon target by PLD method. The results are compared with those obtained for the as-quenched and annealed ribbons regarding both bulk and surface regions. Annealing is performed to induce crystallization in both thin films and ribbons. The crystallization behavior of the FeBSi-type alloys is well known. During the first step of crystallization the bcc-FeSi phase precipitates, while the second one is related to the formation of both bcc-FeSi and tetragonal Fe3B phases [4,5]. At higher annealing temperatures the transformation of the metastable Fe3B phase to a more stable Fe2B one is observed [4]. The chromium addition to the amorphous FeBSi alloy causes the increase of the thermal stability of the amorphous phase and the decrease of the Curie temperature [6,7]. The crystallization temperatures of the amorphous Fe77Cr2B16Si5 alloy determined by differential scanning calorimetry are 536oC and 559oC for the first and second stages, respectively [8]. Transmission Mössbauer spectroscopy was used to characterize the crystallization of the Fe77Cr2B16Si5 ribbon samples as a function of annealing temperature. The conversion electron Mössbauer spectroscopy (CEMS) was applied to obtain structural and magnetic information from the surface layer of the ribbons about 100 nm thick as
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