Dresden 2017 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 56: Bulk Materials: Soft and hard permanent magnets

MA 56.3: Vortrag

Donnerstag, 23. März 2017, 15:30–15:45, HSZ 403

Grain boundary diffusion of different rare earth elements in Nd-Fe-B sintered magnets by experiment and FEM simulation — •Konrad Loewe¹, Dimitri Benke¹, Christian Kübel², Konstantin Skokov¹, and Oliver Gutfleisch¹ — ¹TU Darmstadt, FB Materials Science, 64287 Darmstadt — ²KIT, Institute of Nanotechnology & Karlsruhe Nano Micro Facility, Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

In the present work, we explore the influence of a surface-bulk coercivity gradient in Nd-Fe-B magnets produced by the Grain Boundary Diffusion Process (GBDP) on the overall coercivity. In our systematic and comprehensive study we diffused four different rare earth elements (Dy, Tb, Ce and Gd) in two different kinds of commercial Nd-Fe-B magnets, one very Dy-lean and one Dy-rich. By means of cutting the magnets into thin slices we obtain lateral coercivity profiles, from which diffusion constants are extracted. We find that in both magnets Tb diffuses significantly faster than Dy. Ce diffuses slightly slower than Dy and the overall coercivity decrease is similar for Ce and Gd. High-resolution scanning transmission electron microscopy shows the nano-scale distribution of Tb around the grain boundaries located in the bulk of the magnet. Finally, a simple model for the magnetization reversal in grain boundary diffusion processed gradient Nd-Fe-B magnets was developed and implemented into a FEM software. Our calculated demagnetization curves correspond very well for the Dy and Tb samples, but deviate significantly for Ce and Gd.