Regensburg 2002 – scientific programme

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MA: Magnetismus

MA 2: Mikromagnetismus / Computational Magnetics

MA 2.6: Talk

Monday, March 11, 2002, 11:15–11:30, H22

Magnetic Domains and Magnetization Processes in Sub-micron Soft Ferromagnetic Discs — •Jonathan Ha, Riccardo Hertel, and Jürgen Kirschner — Max Planck Institute für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany

Sub-micron magnetic elements have received much attention for the last few years in part because these magnetic dots show complex domain patterns and unusual hysteresis loops, and because their unique features must be understood if sub-micron devices such as MRAMs are to be used in applications. In this presentation, we report a detailed study of magnetic configurations and magnetization processes of three representative sub-micron soft ferromagnetic disc-shaped elements with diameter-to-thickness ratios of 30 and 100. The computation is done using a finite element method based on micromagnetics principles. The magnetization process begins in saturation, and with decreasing external field, the magnetic configuration can collapse from an almost uniform state to a highly nonuniform vortex state. The configurational transition is a first-order type with a discontinuity in the first derivative of the free energy. An intermediate buckle state is observed in one of the discs. The spread factor function is introduced to measure the degree of spreading of the magnetization. It is shown that the reversal of magnetization can be accomplished with a much smaller field strength than what is expected from the so-called configurational anisotropy by a rotational field applied in the disc plane. This is a way to avoid configurational transitions in magnetization reversal processes.