Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 14: Hauptvortrag Biedermann
O 14.1: Hauptvortrag
Dienstag, 25. März 2003, 10:15–11:00, HSZ/02
Local Atomic Surface Structure of Ultrathin Iron Films and the Invar Alloy — •Albert Biedermann, Michael Schmid, and Peter Varga — Institut für Allgemeine Physik, Vienna University of Technology, A-1040 Vienna
IRON can be prepared in several crystallographic (fcc, bcc) and magnetic (para-, ferro-, antiferro-) states, whose interplay and phase transitions are the basis of many current and future applications. This talk addresses various aspects of the surface structure of ultrathin Fe films: STRUCTURE - Scanning tunneling microscopy enables a direct atom-for-atom access to the local atomic structure of Fe and its martensitic (fcc-to-bcc) transformation. MAGNETISM - A heavily disputed topic concerns the origin of ferromagnetism in ultrathin Fe films on fcc substrates. We show that the ferromagnetism of films grown on Cu can be explained in most cases by a nanocrystalline strained bcc structure. The previously proposed model of a separate ferromagnetic fcc structure does not correctly describe the Fe thin film system. INVAR - Iron rich fcc alloys often show very small and irregular thermal expansion coefficients. The current explanation is based on a magnetovolume effect of an undistorted ferromagnetic fcc structure. Our very recent data of the local surface structure of an Fe65Ni35(100) single crystal are discussed.