Berlin 2005 – wissenschaftliches Programm

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MA: Magnetismus

MA 26: Hauptvortr
äge Fauth / Acet

MA 26.2: Hauptvortrag

Dienstag, 8. März 2005, 14:30–15:00, TU H1028

Magnetic instabilities in Fe₃C (cementite) particles observed with Fe K-edge x-ray circular dichroism under pressure — •Mehmet Acet — Fachbereich Physik, Universität Duisburg-Essen, 47048 Duisburg

The atomic volume is a prime parameter that characterizes electronic properties of solids. Around the equilibrium volume, the electronic structure of a solid can be stable in a relatively broad volume range (20-25 percent) or it can be unstable with respect to an energetically lower lying electronic state by a few meV, when the atomic volume is varied by 3-5 percent. In magnetic solids, the instability of an electronic structure can be detected by probing the magnetic moment while varying the atomic separation by applying hydrostatic pressure. Such instabilities can be found in some 3d-transition metals and alloys incorporating Fe, Mn, and Co as well as in some rare-earth intermetallic compounds. In this report, we present results showing that magnetovolume instabilities can also be present in interstitial solids, specifically in Fe₃C (cementite), for which a rapid change in the magnetic moment is found from about 1.8 µ_B to nearly vanishing values at pressures of about 8 GPa. We show that the Fe K-edge x-ray circular dichroism technique in conjunction with a diamond anvil cell is particularly useful for studying volume dependent magnetic instabilities in Fe alloys and compounds. We examine additionally the equation of state of Fe₃C to show that the rapid change in the magnetic moment is not associated with a structural transformation.