Quantitative identification of constituent phases in a Nd-Fe-B-Cu sintered magnet and temperature dependent change of electron density of Nd2Fe14B studied by synchrotron X-ray diffraction

Hiroyuki Okazaki, David Billington, Naruki Tsuji, Wakana Ueno, Yoshinori Kotani, Shogo Kawaguchi, Kunihisa Sugimoto, Kentaro Toyoki, Tomoki Fukagawa, Takeshi Nishiuchi, Kazuhiro Hono, Satoshi Hirosawa, Tetsuya Nakamura

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

We have measured the temperature dependent XRD profiles of an isotropic Nd-Fe-B-Cu sintered magnet during the annealing process. Through Rietveld refinement, we demonstrate the changes in the volume fractions of a Nd2Fe14B main-phase and the other secondary phases as a function of increasing temperature up to 1047 °C. The secondary phases mainly include dhcp-Nd, fcc-NdOx, and hcp-Nd2O3 at room temperature and fcc-Nd at elevated temperatures. The main phase starts melting above 900 °C but remains relatively stable up to 600 °C, while the dhcp-Nd phase completely disappears at around 600 °C. Taking an advantage of the excellent quality of the XRD profiles in the powdered single crystal sample, we have also investigated the electron density distribution of main-phase by MEM/Rietveld analysis in order to elucidate the origin of the large magnetic anisotropy. The change in asymmetric part of electron density is derived by the subtraction of the electron density distributions between those recorded at -123 and -173 °C, where the spin reorientation transition at -138 °C changes the magnetic anisotropy. This change is attributed to be a difference of electron density distribution between Nd f and g sites of the Nd2Fe14B, relating to the magnetic anisotropy.

Original languageEnglish
Pages (from-to)530-536
Number of pages7
JournalActa Materialia
Volume181
DOIs
Publication statusPublished - 2019 Dec
Externally publishedYes

Keywords

  • Crystal structure
  • Electron density map
  • Nd-Fe-B sintered magnet
  • Synchrotron X-ray diffraction

ASJC Scopus subject areas

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

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