SFB 668


SFB 668

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19.1.2006, 15:30
Jungiusstr. 9, Hörsaal III

SFB 668 - Kolloquium

Dr. Riccardo Hertel (FZ Jülich):

Magnetic Nanostructures: Insights from Finite-Element Modelling

The spatial confinement of the magnetization in ferromagnetic particles of sub-micron size can have a dramatic impact on both the magnetic properties and the spatial arrangement of the magnetization. In the last years, considerable efforts have been made to investigate, understand and control such finite-size effects in nanomagnets. A breathtaking progress has been achieved on the experimental side in terms of magnetic imaging techniques with ever improving spatial resolution and advanced methods of sample fabrication. In terms of understanding, however, numerical simulations are in most cases an indispensable tool to extract detailed quantitative information of the magnetization distribution in nanostructured materials. A reliable and complete analysis of the static and dynamic magnetization in nanostructures can usually only be obtained by combining experiments and simulations. The theory of micromagnetism provides the basic equations to describe the magnetization in mesoscopic particles. Since these equations can generally only be solved numerically, accurate micromagnetic simulations are required for a detailed description of the magnetization. While accurate solutions of the micromagnetic equations can be obtained for particles of simple rectangular shape using standard methods employed in public-domain computer codes, the accurate modelling of the particle shape frequently represents a serious difficulty in the case of particles of general geometry containing, e.g., inclined facets or curved boundaries. The finite-element method is rarely used in numerical micromagnetism, although its geometrical flexibility is particularly powerful to study the influence of the particle shape on the magnetic properties of nanostructures. In this talk, I will introduce the basics of a finite-element formulation for micromagnetic simulations and I will discuss several examples on the static magnetic structures and dynamic magnetization processes predicted for mesoscopic particles like nanowires, thin-film elements and self-organized magnetic islands. In most cases, a remarkable agreement is found in the direct comparison of experimental and numerical results. Micromagnetic simulations can provide information that is not available in the experiment, like e.g. the three-dimensional magnetic structure in particles of elevated thickness (ca. 100 nm).

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