The effect of high oxygen pressure for La-Co SrM ferrite -for high performance ferrite magnets-

• Project/Area Number: 17K14811
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Inorganic materials/Physical properties
• Research Institution: Kyoto University
• Principal Investigator: Waki Takeshi 京都大学, 工学研究科, 助教 (50463906)
• Project Period (FY): 2017-04-01 – 2019-03-31
• Project Status: Completed (Fiscal Year 2018)
• Budget Amount: ¥4,420,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥1,020,000); Fiscal Year 2018: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2017: ¥2,990,000 (Direct Cost: ¥2,300,000、Indirect Cost: ¥690,000)
• Keywords: 高性能フェライト磁石 / La-Co SrMフェライト / 磁気異方性 / 酸素分圧 / 磁性

Outline of Final Research Achievements

La-Co co-substituted magnetoplumbite-type (M-type) strontium ferrite is typically used as a base material for high-performance hard ferrite magnets. Generally, the unquenched orbital moment of Co2+, substituted for Fe3+, is thought to enhance magnetic anisotropy and then coercivity. La3+ is substituted for Sr2+ to compensate for the charge unbalance associated with Co2+ substitution. Even if the synthesis starts with equal amounts of Co and La, the Co contents of the resulting samples are generally lower than the La contents because of the partial reduction of Fe3+ to Fe2+. We studied how the oxygen potential suppresses the formation of Fe2+ and expands the Co solubility range in this system.We reveal that the application of higher oxygen pressure dramatically expands the Co solubility range, resulting in the enhancement in magnetic anisotropy. We successfully synthesized Sr-free LaFe11CoO19 with high magnetic anisotropy using the hot isostatic pressure (HIP) technique.

Academic Significance and Societal Importance of the Research Achievements

本研究では、La-Co共置換SrMフェライトのCo置換量上限が酸素分圧に非常に敏感であることを初めて明らかにしたものである。得られた試料が高性能フェライト磁石の母材として非常に有望な優れた磁気異方性を有していることを発見したことが重要な成果である。

Research Products

• [Journal Article] Co site preference and site-selective substitution in La-Co co-substituted magnetoplumbite-type strontium ferrites probed by 59Co nuclear magnetic resonance (2019)
  • Author(s): H. Nakamura, T. Waki, Y. Tabata, C. Meny
  • Journal Title: J. Phys.: Mater Volume: 2 Issue: 1 Pages: 015007-015007
  • DOI: 10.1088/2515-7639/aaf540
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Single-crystal growth and magnetic properties of Co-substituted Ca-La magnetoplumbite-type ferrite (2019)
  • Author(s): Waki T.、Uji K.、Tabata Y.、Nakamura H.
  • Journal Title: Journal of Solid State Chemistry Volume: 270 Pages: 366-369
  • DOI: 10.1016/j.jssc.2018.11.036
  • Peer Reviewed
• [Journal Article] Occupation sites and valence states of Co dopants in (La, Co)-codoped M-type Sr ferrite: 57Fe and 59Co nuclear magnetic resonance studies (2018)
  • Author(s): H. Sakai,* T. Hattori, Y. Tokunaga, and S. Kambe, H. Ueda, Y. Tanioku, C. Michioka, and K. Yoshimura, K. Takao, A. Shimoda, T. Waki, Y. Tabata, and H. Nakamura
  • Journal Title: Phys. Rev. B Volume: 98 Issue: 6 Pages: 064403-064403
  • DOI: 10.1103/physrevb.98.064403
  • Peer Reviewed / Open Access
• [Journal Article] Effect of oxygen potential on Co solubility limit in La-Co co-substituted magnetoplumbite-type strontium ferrite (2018)
  • Author(s): Waki T.、Okazaki S.、Tabata Y.、Kato M.、Hirota K.、Nakamura H.
  • Journal Title: Materials Research Bulletin Volume: 104 Pages: 87-91
  • DOI: 10.1016/j.materresbull.2018.03.057
  • Peer Reviewed