Fe tracer diffusion in L1 0 ordered FePt
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Fe tracer diffusion in L10 ordered FePt Y. Nosé1, T. Ikeda1, H. Nakajima1, K. Tanaka2* and H. Numakura2 1 The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan 2 Department of Materials Science and Engineering, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan ABSTRACT Tracer diffusion coefficient of 59Fe in FePt with the tetragonal L10 ordered structure has been measured by an ion-beam sputter-sectioning technique in the temperature range from 1173 to 1374 K. Anisotropy in diffusion has been studied using single-variant single-crystal specimens. The diffusion coefficient in the direction perpendicular to [001] axis (in the a-axis direction), Da, is larger than that in the [001] (c-axis) direction, Dc, as expected from the atomic arrangement of the L10 ordered structure. The ratio of the diffusion coefficients, Da/Dc, is 1.3_3.6 for Fe42Pt58 and smaller at higher temperatures. The activation energy for the diffusion is 259 ± 1 kJ/mol for Da and 309 ± 18 kJ/mol for Dc, while the pre-exponential factor is (1.63−+00..1315 ) × 10 −6 m2/s and (8.47−+636.88.5 ) × 10 −5 m2/s, respectively in Fe42Pt58.
INTRODUCTION Intermetallic compounds have recently attracted much attention as a potential structural material for high temperature use or a functional material. The knowledge of diffusion is essential to understand properties of compounds from a fundamental point of view. Diffusion is also a basic process in various phenomena occurring in materials. Therefore, knowledge of diffusion is important for the fabrication of materials and also for practical use. For Fe–Pt system, the tracer diffusion coefficients of 193mPt in Fe–Pt alloys were measured by Kucera and Million [1], and Cermak and Kucera [2]. The present authors have reported the tracer diffusion coefficient of Fe and the chemical diffusion coefficient in Pt3Fe [3-5] and FePt [5,6]. In this system there are three ordered phases [7], Pt3Fe (L12), FePt (L10) and Fe3Pt (L12). Particularly, FePt attracts much attention as a magnetic material and has been studied for an application to magnetic thin films. Figure 1 shows the tetragonal L10-ordered structure. In this arrangement of atoms, the planes of A (Fe) atoms and those of B (Pt) atoms alternately stack in the [001] direction. Thus, the diffusion is expected to be anisotropic in the tetragonal crystals; there are two independent coefficients Da and D c, which are the diffusion coefficients in the directions perpendicular and parallel to [001] (in the a-axis and c-axis directions), respectively. However, in FePt, Kucera and Million did not investigate the anisotropy of diffusion because of *
Present address: Department of Advanced Materials Science, Faculty of Engineering, Kagawa University, Hayashicho 2217-20, Takamatsu 761-0396, Japan
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usage of the polycrystalline specimens. In the present work, we have measured the tracer diffusion coefficient of Fe in the ordered FePt alloy using single-crystal specimens consisting
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