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M: Metallphysik

M 22: Intermetallische Phasen

M 22.1: Vortrag

Mittwoch, 10. März 2004, 16:30–16:45, H6

Ordering and Magnetism in Fe-Co: Quasi-Continuous Sequence of Ground-State Structures — •Ralf Drautz¹, Alejandro Diaz-Ortiz², Manfred Fähnle³, and Helmut Dosch³ — ¹Department of Materials, University of Oxford, OX1 3PH, UK — ²Advanced Materials Department, Instituto Potosino de Investigacion Cientifica y Tecnologica, A.C., 78231 San Luis Potosi, S.L.P., Mexico — ³Max-Planck-Institut für Metallforschung, Heisenbergstraße 3, D-70569 Stuttgart

We have discovered that Fe-Co alloys develop a series of ordered ground-state structures for different compositions additionally to the known CsCl-type structure. This new set of ground-state structures was found from a combinatorial ground-state search of 1.5×10¹⁰ bcc-based structures. The energies of the searched bcc structures were constructed with the cluster expansion method from few first-principles calculations for ordered Fe-Co structures.

To explain the sequence of ordered ground-state structures found in FeCo, a hypothesis for the precondition to find a continuous sequence of ground states in a binary alloy is proposed. In accordance with our findings from the combinatorial ground-state search the system FeCo is found to slightly violate the conditions for a continous ground state. This naturally explains the found finite set of ground state structures.