Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 2: Micro and Nanostructured Magnetic Materials I

MA 2.7: Vortrag

Montag, 25. Februar 2008, 11:45–12:00, EB 301

Size dependence of the magnetization switching field of nano-island — •Guillemin Rodary, Sebastian Wedekind, Dirk Sander, and Jürgen Kirschner — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle (Saale), Deutschland

We have explored the magnetization switching field of Co nano-islands grown on Cu(111). We apply spin-polarized scanning tunneling microscopy (SP-STM) at 7 K to measure the magnetocurrent hysteresis loop of a magnetic tunnel junction composed of a single nanostructure and the magnetic tip of the STM. We measure directly the magnetic response by spin-dependent scanning tunneling spectroscopy of an individual Co nano-island as a function of magnetic field of up to 4 T, oriented perpendicular to the sample surface [1].

We observe a transition from superparamagnetic to ferromagnetic behavior with increasing island size. In the ferromagnetic state, the switching of the magnetization of the island is identified by a sharp drop of the differential conductance as a function of magnetic field. Switching fields of the order of 1 T are observed [2], and we discuss our result in view of the Stoner-Wohlfarth model of magnetization rotation and also with regard to magnetic domain formation. Our work opens the way for studies of magnetic anisotropy of single nano-objects.

[1] G. Rodary, S. Wedekind, D. Sander and J. Kirschner, unpublished.

[2] O. Pietzsch, A. Kubetzka, M. Bode and R. Wiesendanger, Phys. Rev. Lett. 92, 057202 (2004).