66 research outputs found
Studies of atomic scale diffusion by quasielastic Mößbauer spectroscopy and x-ray photon correlation spectroscopy
No full textQuasielastic Mößbauer Spectroscopy (QMS) has proven successful in investigating diffusive dynamics at the atomic level in solid state physics [1]. Due to the high energy resolution that is demanded by such experiments, it is however restricted to systems at rather high temperatures (close to the melting point). Furthermore QMS is naturally limited to certain kinds of isotopes. The goal of our studies in the last years was to find a new method to study atomic motion at the fundamental level which overcomes these limitations. Over the last years the relatively new technique of x-ray photon correlation was expanded by our group to work on the atomic scale. Measuring chemical fluctuations rather than self diffusion, this technique operates in the time regime and not in the energy regime. It is therefore possible to study systems at much lower temperatures with atomic scale x-ray photon correlation spectroscopy (aXPCS). It allows to investigate atomic scale diffusion in glasses well below glass transition temperatures and in the temperature range of intermetallic phases. The time resolution towards faster dynamics is only limited by the readout time of the detector and intensity of the x-ray beam and towards slower dynamics it is limited by the stability and the duration of the experiment. It is furthermore not restricted to certain elements, even though at the moment a high contrast between scattering elements under investigation is required due to today’s technical limitations at synchrotron sources.Fig. 1 Schematic setup of an aXPCS experiment Since the first successful aXPCS experiment was carried out only a few years ago [2], we continuously refined this method. One of the driving factors for a rapid progress of aXPCS was the fast improvement in the brilliance of synchrotron sources over the last years. This poster will compare results obtained for an Fe-Al system, measured both with QMS [1,3] and with aXPCS. Furthermore the challenges and drawbacks of both approaches will be discussed, e.g. the influence of short range order in the coherent method of aXPCS. This work was supported by the Austrian Science Fund (FWF): P22402. [1] G. Vogl and B. Sepiol, Acta Metall. Mater. 42 (1994) 3175.[2] M. Leitner, B. Sepiol, L.-M. Stadler, B. Pfau and G. Vogl, Nature Mat. 8 (2009) 717.[3] R. Weinkamer, P. Fratzl, B. Sepiol, and G. Vogl, Phys. Rev. B 59 (1999) 8622
Vibrational thermodynamics of Fe90Zr7B3 nanocrystalline alloy from nuclear inelastic scattering
No full textRecently we determined the iron-partial density of vibrational states (DOS) of nanocrystalline Fe(90)Zr(7)B(3) (Nanoperm), synthesized by crystallization of an amorphous precursor, for various stages of nanocrystallization separating the DOS of the nanograins from that of the interfaces [S. Stankov, Y. Z. Yue, M. Miglierini, B. Sepiol, I. Sergueev, A. I. Chumakov, L. Hu, P. Svec, and R. Ruffer, Phys. Rev. Lett. 100, 235503 (2008)]. Here we present quantitative analysis of the evolution of various thermoelastic properties calculated from DOS such as mean-force constant, mean atomic displacement, vibrational entropy, and lattice specific heat as the material transforms from amorphous, through nanocrystalline, to fully crystallized state. The reported results shed new light on the previously observed anomalies in the vibrational thermodynamics of nanocrystalline materials
Dynamics in FePt thin films
No full textThe magnetocrystalline and thermal stability of L10-FePt makes this alloy suitable for ultrahigh density recording. The possible impact on recent data storage devices makes a detailed knowledge of the dynamic processes essential for selectively designing alloys with diverse physical properties. Various experiments with bulk L10-FePt dealing with diffusion and ordering dynamics have been performed [1, 2].
Here we report on investigations helping to understand the mechanisms working in thin film dynamics. Namely we report on diffusion of iron atoms parallel and perpendicular to the c-axis of the L10 structure within FePt thin films grown on MgO substrates [1]. Further our recent studies showed that the L10 order of the c-variant (easy axis of the magnetic field out of the film plane) spontaneously re-orient creating a-variant domains (easy axis of the magnetic field in the film plane). Surprisingly the effect reverts after longer annealing times, leading to a recovery of the c-variant and finally reaches a saturated state. We present an adapted Johnson-Mehl-Avrami model which allows to determine in detail the dynamical mechanisms in the thin film, their activation energies and characteristic times.
[1] M. Rennhofer, B. Sepiol, M. Sladecek, D. Kmiec, S. Stankov, G. Vogl, M. Kozlowski, R. Kozubski, A. Vantomme, J. Meersschaut, R. Rüffer and A. Gupta. Phys. Rev. B. 74(10), 104301 (2006).
[2] R. Kozubski, M. Kozlowski, K. Zapala, V. Pierron-Bohnes, W. Pfeiler, M. Rennhofer, B. Sepiol and G. Vogl, J. of Phase Equil. and Diff. 26(5), 482-486 (2005).
[3] M. Rennhofer, M. Kozlowski, B. Laenens, B. Sepiol, R. Kozubski, A. Vantomme
and G. Vogl. to be published (2008)
Gniazdowanie dzieciola duzego Dendrocopos major i innych gatunkow ptakow w norach zolny.
No full textDetermination of The Diffusion Mechanism by A Method with New Possibilities: Nuclear Scattering of Synchrotron Radiation
No full textABSTRACTThe elementary diffusion jump in crystalline solids can be determined by methods derived from nuclear physics. With these methods not only diffusion rate(s) but also diffusion vector(s), i.e. the complete diffusion mechanism can be deduced. We report on a new method for probing the elementary diffusion jumps in crystalline lattices on an atomistic scale and demonstrate its potential by a study of 57Fe diffusion in different intermetallic alloys. Compared to the results of conventional tracer (macroscopic) technique, the new method provides clear and doubtless statements concerning the direction and distance of elementary jumps. One can also determine (though less precisely than with tracer diffusion), iron diffusion coefficients.</jats:p
Kolejne stanowiska oblaczka granatka Syntomis phegea Linnaeus [Lepidoptera: Arctiidae] w krainie Gor Swietokrzyskich
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Results of winter counts of birds of prey Falconiformes and great grey shrikes Lanius excubitor in selected valleys of the Swietokrzyskie Mountains
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