Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 36: Magnetic Particles and Clusters II

MA 36.12: Vortrag

Donnerstag, 26. März 2009, 18:00–18:15, HSZ 401

Stability of the magnetic domain structure of nanoparticle thin films against external fields — •Kai-Felix Braun¹, S. Sievers¹, M. Albrecht¹, U. Siegner¹, K. Landfester², and V. Holzapfel² — ¹Physikalisch-Technische Bundesanstalt, 38116 Braunschweig. — ²Max Planck Institute for Polymer Research, 55128 Mainz.

We investigate the influence of an external magnetic field on the magnetic ordering of single-layer and multi-layer thin films of magnetic nanoparticles (MNP). It is shown that the dipolar interaction results in a larger stability of multi-layer films as compared to single-layer films when exposed to inhomogeneous fields generated, e.g. by the magnetized tip of a magnetic force microscope (MFM). Numerical calculations and experimental MFM studies are presented. The calculations show that unperturbed single-layer MNP films display an in-plane domain pattern which is induced by dipolar interaction. Yet, even in the presence of this collective effect, external fields can rotate the spins of the MNPs out of plane. In MFM images an out-of-plane configuration manifests itself by a contrast enhancement at the film edge. This theoretical prediction is confirmed by the experimental MFM images of a single-layer film. Multi-layer films are found to be more robust against external fields than monolayers. Both calculated and measured MFM images show that the domain pattern of multi-layer films is still oberved under external fields that prevent the observation of the domain pattern of single-layer films. The nature of the collective reaction on the external perturbation will be discussed in detail and will be compared to non-interacting MNPs.