Regensburg 2004 – wissenschaftliches Programm

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O: Oberflächenphysik

O 7: Hauptvortrag Bansmann

O 7.1: Hauptvortrag

Montag, 8. März 2004, 14:00–14:45, H36

Magnetism of mass-filtered nanoparticles on ferromagnetic supports — •Joachim Bansmann — Fachbereich Physik, Universität Rostock, Universitätsplatz 3, D-18051 Rostock

The magnetic properties of 3d-metal clusters significantly differ from bulk behavior. In small clusters with less than 500 atoms the magnetic moments are enhanced and strongly depend on the number of atoms within each cluster. Such phenomena are caused by a narrowing of electronic states and the high ratio of surface to bulk giving rise to large magnetic orbital moments. However, even large Fe nanoparticles on cobalt with up to 100.000 atoms per cluster showed enhanced orbital moments.

Here, I will report on results obtained from element-specific X-ray Magnetic Circular Dichroism (XMCD) studies at mass-filtered Fe and FeCo alloy clusters (6 - 12 nm) deposited onto ferromagnetic surfaces. At a low coverage XMCD data for large iron clusters on a cobalt film display enhanced orbital moments with nearly a doubled value when compared to bulk behaviour. With increasing coverage, the orbital moment is clearly reduced. The data are compared to much smaller iron clusters.

Moreover, Fe_0.5Co_0.5 alloy clusters on a nickel substrate have been investigated. According to the Slater-Pauling curve, FeCo alloys exhibit the highest magnetic moments for soft magnetic materials. When searching materials with even higher saturation magnetizations, FeCo alloy clusters might be ideal candidates. The spin and orbital moments of iron and cobalt in FeCo nanoparticles with sizes of 6 nm and 7.5 nm have been determined. Enhanced orbital moments may play the dominant role although their contributions are smaller than the spin moments.