Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 31: Magnetic Particles and Clusters I

MA 31.1: Vortrag

Donnerstag, 26. März 2009, 10:15–10:30, HSZ 401

Direct characterization of the superparamagnetic-ferromagnetic transition of single nano-islands — •Guillemin Rodary, Sebastian Wedekind, Hirofumi Oka, Dirk Sander, and Jürgen Kirschner — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120, Halle, Germany

The transition from a superparamagnetic to a ferromagnetic state is studied on single Co nano-islands by spin-polarized scanning tunneling spectroscopy. Magnetic hysteresis loops of the local differential conductance on individual island are measured [1] as a function of the size of the nanostructure and of the temperature. A clear transition of magnetic response from a hysteresis free to a hysteretic behavior due to magnetization direction switching [1] is observed when increasing the island size. This is ascribed to the superparamagnetic to ferromagnetic transition. The same transition is demonstrated to be also accessible by decreasing the temperature and crossing the blocking temperature. We find a blocking temperature of 10 K for an island of 1010 atoms. We discuss these experimental results in the perspective of a simple model of thermally activated magnetization switching that allows quantitative finding of local magnetic anisotropy.

[1] G. Rodary, S. Wedekind, D. Sander, and J. Kirschner, JJAP (in press)