Dresden 2017 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 56: Bulk Materials: Soft and hard permanent magnets

MA 56.7: Vortrag

Donnerstag, 23. März 2017, 16:45–17:00, HSZ 403

Impact of dislocations on coercivity in L1₀-MnAl — •Florian Bittner¹, Jens Freudenberger^1,2, Ludwig Schultz¹, and Thomas G. Woodcock¹ — ¹IFW Dresden, Institute for Metallic Materials, PO Box 270116, 01171 Dresden, Germany — ²TU Bergakademie Freiberg, Institute of Materials Science, Gustav-Zeuner-Straße 5, 09599 Freiberg, Germany

Novel rare-earth free hard magnetic compounds are of growing interest due to the demand for permanent magnets with maximum energy densities between those of ferrites and rare earth magnets. The L1₀ ordered τ-MnAl is one candidate material for applications due to its promising intrinsic magnetic properties. Even though the anisotropy field is approximately 5 T, the coercivity achieved in bulk magnets is currently too low to reach its full potential. The reason for this discrepancy is caused by the microstructure of the material and the impact microstructural features on the magnetic properties. The coercivity of cold worked Mn₅₄Al₄₆ is remarkably increased from 0.02 T in the initial state to 0.29 T. Further annealing reduces coercivity while the microstructure remains unchanged within the resolution limit of the scanning electron microscope. Direct analysis of the quality of electron backscatter diffraction patterns was used to approximate the local dislocation density in the materials. The results showed significant evidence for different dislocation densities in the different metallurgical conditions. The conclusion that dislocations can act as pinning sites is also supported by the shape of the initial magnetisation curve and explained by local changes of the intrinsic magnetic properties.