[O4] Characterization

3:45 PM - 4:00 PM JST(6:45 AM - 7:00 AM UTC)

[O4-2] 2D and 3D magnetic imaging of interaction domains in nanostructured Nd₂Fe₁₄B using X-ray imaging techniques

Philipp Klaßen¹, Damian Günzing^1,6, Alex Aubert², Thomas Feggeler^4,6, Benedikt Eggert¹, Jeffrey Neethirajan⁵, Lukas Schäfer², Fernando Maccari², Manuel Guizar-Sicairos^3,7, Valerio Scagnoli^3,8, Mirko Holler³, David Shapiro⁶, Alex Ditter⁶, Enrico Bruder², Heiko Wende¹, Konstantin Skokov², Claire Donnelly⁵, Oliver Gutfleisch², *Katharina Ollefs¹ (1. University Duisburg-Essen (Germany), 2. Technical University Darmstadt (Germany), 3. Paul Scherrer Institut (Switzerland), 4. National Synchrotron Light Source II (United States of America), 5. Max-Planck-Institute for Chemical Physics of Solids (Germany), 6. Lawrence Berkeley National Laboratory (United States of America), 7. École Polytechnique Fédérale de Lausanne (Switzerland), 8. ETH Zurich (Switzerland))

Keywords:

2-14-1,x-ray imaging,nanostructured magnets

We present insights into the 2D and 3D magnetic domain structure of nanostructured Nd-Fe-B magnets obtained by advanced imaging techniques such as ptychographic X-ray laminography using synchrotron X-rays. Nanostructured Nd₂Fe₁₄B magnets have a very fine grain structure of a few 100 nm in width, which is approximately the single domain particle size, in contrast to sintered magnets which have a much coarser grain structure. The fine grain structure of nanostructured magnets offers great potential for improving magnetic properties by controlling the microstructure. Nanostructured magnets exhibit cooperative phenomena such as interaction domains, where the magnetic domains are much larger than the grains themselves. Their formation can be attributed to both exchange and magnetostatic interactions of the grains, depending on the elemental and phase composition. A deeper understanding of the interplay between the underlying microstructure and the resulting magnetic properties is crucial to improve the magnetic performance of such materials. We have imaged the magnetic interaction domain structure within the bulk of a nanostructured hot deformed anisotropic nanocrystalline Nd₁₅Fe₇₈B₈ magnet to correlate the crystal structure and magnetic moment configuration. Here, a Nd-rich boundary phase decouples the grains with respect to exchange interactions. We show that surface effects, such as flux closure domains, do not dominate the magnetic domain pattern at the surface and reveal the complex domain structure in deeper regions of the permanent magnet. Furthermore, we have imaged the interaction domain structure of these anisotropic nanocrystalline Nd₁₅Fe₇₈B₈ magnets in 2D in comparison to isotropic Nd₁₅Fe₇₈B₈ and single-phase Nd₂Fe₁₄B melt spun ribbons. These measurements are complemented by surface sensitive studies using Kerr microscopy, magnetic force microscopy and electron microscopy. This study advances our understanding of interaction domain size, their domain energy and wall character. We acknowledge funding by the Deutsche Forschungsgemeinschaft (DFG) within the CRC/TRR 270 (Project-ID 405553726).