Workshop on

numerical methods for multiscale problems

 

     
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  Hermann Forster: Multiscale problems in micromagnetics

Current problems in magnetic device modeling involves length scales ranging from a few nanometers up to several micrometers. In this talk we will present examples of multiscale problems in micromagnetics: (1) Simulation of the magnetic recording process requires a realistic model of the recording h ead and the recording media. The recording media itself may consist of a data layer and a soft underlayer. The characteristic features of the recorded bits depends on magnetization processes on a length scale of a few nanometers such as the fast reversal of the individual magnetic grains of the data layer and domain wall processes in the soft underlayer. Magnetostatic interactions between the moving head and the media extend over a length scale of micrometers. (2) High performance permanent magnets have a grain size in the order of one micrometer. The coercivity mechanisms, nucleation of domains or domain wall pinning, depend on microstructural features in the size of nanometers. Different numerical methods are used to tackle these problems. A multiple misstep integration scheme was developed to treat the long range magnetostatic interactions in dynamic micromagnetic simulations. The magnetostatic interaction between distinct and/or moving magnetic parts is computed by a boundary element method. Different ways to sparsify the BEM-matrix are compared: A treecode as used for particle simulations are used for magnetostatic problems with moving parts. Hierarchical matrices improves the performance in large scale micromagnetic problems.
Impressum
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