Berlin 2015 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 40: Electronic Structure of Magnetism, Micromagnetism, Computational Magnetism (organized by MA)

TT 40.10: Vortrag

Dienstag, 17. März 2015, 12:00–12:15, H 0112

Micromagnetic analysis of nucleation and pinning processes in supermagnetsDagmar Goll1, Therese Dragon2, Matthias Katter3, and •Helmut Kronmueller21Aalen University, Materials Research Institute (IMFAA), Aalen — 2Max Planck Institute for Intelligent Systems — 3Vacuumschmelze GmbH & Co. KG, Hanau

The large discrepancy between theoretical predictions and realized magnetic properties of hysteresis loops of high-quality permanent magnets, known as Brown-paradox, has been the matter of discussions over decades of years. In particular whether the leading hardening mechanism is due to a nucleation mechanism or to domain wall pinning has been the topic of many publications with contrary statements. Here the existence of single or multi-domain grains plays a central role. This contribution presents the following basic results which allow a distinction between the two types of hardening mechanisms: 1. Coercive field Hc as a function of maximum applied magnetic field. 2. Change of domain patterns as a function of applied magnetic field. 3. Angular dependence of Hc. 4. Temperature dependence of Hc. Experimental results obtained for nanocrystalline systems of FePt and MnBi and sintered Nd-Fe-B based permanent magnets are compared with micromagnetic analytical results. It is shown that for high-quality permanent magnets the dominant hardening mechanism corresponds to the nucleation process.

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