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MA: Fachverband Magnetismus

MA 14: Poster Ib: Magnetic Materials (1-14); Micro Magnetism/Computational Mag. (15-17); Surface Magnetism (18-22); Spin Structures/Phase Transitions (23-25)

MA 14.16: Poster

Dienstag, 24. März 2009, 10:15–13:00, P1B

High resolution large-scale micromagnetic simulations with hierarchical matrices — •Attila Kákay and Riccardo Hertel — Institute for Solid State Research, Research Center Jülich GmbH, 52428 Jülich, Germany

The hybrid finite element/boundary element method (FEM/BEM) [1] is a powerful, high precision method in micromagnetic simulations. The BEM is used to map the open boundary conditions of the magnetostatic potential at infinity on equivalent boundary conditions at the surface of the magnetic region. However, the calculation of the magnetostatic potential involves a densely populated matrix which for large problems can become of considerable size (up to several TBytes), since it is proportional to the square of the number of boundary nodes. The hierarchical matrices or H-matrix technique [2] can be used to drastically reduce the size of the dense matrix, without significant loss in accuracy. We present applications of this technique to micromagnetic problems of such size and complexity what could not be addressed before. The examples include the cross-tie domain wall structure and its field-pulse induced dynamics in a long Permalloy stripe (1 um) and a study on the fine details of the magnetic structure in a large (5 um) Permalloy disk. These magnetic structures involve three different length scales: domain size, domain wall width and vortex core width. The calculated domain configuration for both examples is in very good agreement with experiments.[1] D.R. Fredkin and T.R. Koehler, J. Appl. Phys. 63, 3385 (1988) [2] S. Boerm and L. Grasedyck, HLib - A library for H - and H2 - atrices,1999,http://www.hlib.org/