Relationship between the microstructure, local magnetism and coercivity in Ga-containing Nd-Fe-B sintered magnets

David Billington, Hiroyuki Okazaki, Kentaro Toyoki, Yoshinori Kotani, Yukio Takada, Takashi Sato, Yuji Kaneko, Akira Kato, Taisuke T. Sasaki, Tadakatsu Ohkubo, Kazuhiro Hono, Tetsuya Nakamura

Research output: Contribution to journalArticlepeer-review

Abstract

The crystalline phases that comprise the bulk microstructure of an isotropic Ga-containing Nd-Fe-B sintered magnet are identified by in situ elevated-temperature x-ray diffraction for temperatures between 25 and 800C. Comparing the temperature-dependent volume fractions of the crystalline phases with the coercivity as a function of annealing temperature reveals that the large coercivity enhancements are remarkably well-correlated with the existence of a crystalline Nd6(Fe,Ga)14 phase. Scanning soft x-ray absorption microscopy measurements are used to directly observe the distribution of Fe and Nd in anisotropic as-sintered and optimally-annealed samples and demonstrate that the surface microstructure is similar to the bulk. Fe L3-edge x-ray magnetic circular dichroism measurements are used to directly map the demagnetization process in the fractured surfaces of anisotropic as-sintered and optimally-annealed samples. In the as-sintered sample, the demagnetization curves of compositionally different regions all have the same shape but with a maximum magnetic signal that only depends on the Fe content within the probing depth of the x-ray absorption measurements. In the optimally-annealed sample, the demagnetization curves from compositionally different regions have rather different shapes and the exposed Nd2Fe14B grains without any grain boundary coverage have much lower coercivity than those with. This provides evidence that the grain boundary phase that forms upon annealing is able to protect the Nd2Fe14B grains from magnetization reversal by exchange-decoupling the Nd2Fe14B grains.

Original languageEnglish
Article number116517
JournalActa Materialia
Volume205
DOIs
Publication statusPublished - 2021 Feb 15
Externally publishedYes

Keywords

  • Magnetic domains
  • Nd-Fe-B
  • XMCD
  • XRD

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

Fingerprint Dive into the research topics of 'Relationship between the microstructure, local magnetism and coercivity in Ga-containing Nd-Fe-B sintered magnets'. Together they form a unique fingerprint.

Cite this