Regensburg 2004 – wissenschaftliches Programm
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M: Metallphysik
M 8: Phasenumwandlungen I
M 8.2: Vortrag
Montag, 8. März 2004, 15:00–15:15, H4
Magnetic effects on the nucleation in undercooled Co-Pd melts — •Dirk Holland-Moritz1,2 and Frans Spaepen2 — 1DLR, Institut für Raumsimulation, D-51170 Köln — 2Harvard University, Division of Engineering and Applied Sciences, Cambridge, MA 02138, USA
For all known ferromagnetic metallic materials the Curie temperature is lower than the liquidus temperature. Therefore, ferromagnetism has not been observed in stable metallic melts. By use of advanced undercooling techniques it is however possible to undercool melts of Co-based alloys near their Curie temperature. Preceding undercooling experiments on melts of Co-Pd alloys as a function of the alloy composition indicated a change of the nucleation mechanism if the temperature of the liquid is approaching the Curie temperature. Therefore the measured composition dependence of the nucleation temperatures cannot be described in the framework of classical nucleation theory.
In this work we present a thermodynamic model which extends classical nucleation theory by adding magnetic contributions to the driving free energy for crystallization. The inclusion of these contributions allows a quantitative description of experimental results on the undercoolability of Co-Pd melts in the entire composition range from 50-100 at.% Co.
This work was supported by the Deutsche Forschungsgemeinschaft (DFG) under contract Nos. Ho1942/1 and Ho1942/2, by the Alexander von Humboldt Stiftung and by the National Space and Aeronautics Administration (NASA).