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MM: Fachverband Metall- und Materialphysik

MM 36: Topical Session Electron Theory V

MM 36.2: Topical Talk

Thursday, March 17, 2011, 14:30–15:00, IFW A

High-performance permanent magnets - significance of thermodynamics, kinetics and microstructure — •Gerhard Schneider and Dagmar Goll — Aalen University, Materials Research Institute, Beethovenstr. 1, 73430 Aalen

High-performance permanent magnets (pms) like NdFeB magnets are based on outstanding intrinsic and extrinsic (microstructural) magnetic properties. Excellent intrinsic properties as high saturation polarization and large magnetic anisotropy are achieved by combining transition-metal atoms and rare-earth atoms. For outstanding extrinsic properties ideally µm- or nm-scaled textured hard magnetic grains of ellipsoidal shape are required separated by a nonmagnetic grain boundary phase from each other. However, in NdFeB sintered pms deviations ("structural defects") from this ideal microstructure occur due to the chosen alloy composition in the phase diagram (including additives), powder processing, sintering and annealing conditions. As a consequence the microstructure is characterized by hard magnetic grains of polyhedral shape which are completely or partly surrounded by grain boundary phases (metastable magnetic phases, nonmagnetic phases (η-phase, rare earth oxides)) and pores. Especially the metastable phases which crystallize out of a liquid phase at sintering form a complex structure below the eutectic solidification temperature of 650 ^∘C and influence the magnetic properties. The presentation highlights the thermodynamics and kinetics of the grain boundary phases. The systematic quantitative investigation of character and composition of these phases enables a specific tailoring of the properties of high-performance pms.