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Dresden 2009 – scientific programme

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MA: Fachverband Magnetismus

MA 25: Micro- and Nanostructured Magnetic Materials II

MA 25.17: Talk

Wednesday, March 25, 2009, 19:00–19:15, HSZ 403

Quasi-Antiferromagnetic 120 Néel-State in 2D Clusters of Dipole-Quadrupole-Interacting Particles Arranged on a Hexagonal Lattice — •Nikolai Mikuszeit1, Larysa Baraban2, Elena Y. Vedmedenko1, Artur Erbe2, Paul Leiderer2, and Roland Wiesendanger11Institute of Applied Physics, University of Hamburg Jungiusstr. 11, 20355 Hamburg, Germany — 2Department of Physics, University of Konstanz, Universitätsstr. 10, Konstanz, 78457, Germany

Recent experiments on colloidal particles, capped with Co/Pt multilayers, have shown a 120 Néel-state [1], which was unexpected for particles interacting via stray field. The state, where all particles are reversed, is not observed. In the framework of multipole expansion [2] this asymmetry requires not only odd but also even parity moments (e.g. a quadrupole (q)). The even parity moments significantly alter the dipolar ordering of the presumably dominant dipole (d).

We performed Monte Carlo simulations of particle clusters taking into account a d- and a q-moment. Although the symmetries of the pure dipolar (vortex) or pure quadrupolar (pinwheel) ground states strongly differ from the observed Néel-state, the latter one can be established by competing d and q interactions. The relative strength of d-d- and q-q-interaction as well as the cluster size was varied. A small region was found, where the 120 Néel-state is formed.
L. Baraban, et al. Phys. Rev. E 77, 031407 (2008)
E. Y. Vedmedenko and N. Mikuszeit, ChemPhysChem, 9, 1222 (2008)

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