成果報告書詳細
管理番号20110000001388
タイトル*平成22年度中間年報 希少金属代替材料開発プロジェクト 希土類磁石向けディスプロシウム使用量低減技術開発(3)
公開日2011/12/13
報告書年度2010 - 2010
委託先名国立大学法人山形大学
プロジェクト番号P08023
部署名電子・材料・ナノテクノロジー部
和文要約和文要約等以下本編抜粋:1. 研究開発の内容及び成果等 研究開発項目(1)「界面ナノ構造制御による保磁力向上技術の開発」 (2)~2 高保磁力磁石の焼結組織最適化に関する研究【山形大学】【緒言】本研究では薄膜プロセスを用いて,主相であるNd2Fe14B 粒子表面へ擬似的なNd-rich 粒界相物質を堆積してモデル界面を形成させることで,高い保磁力を持つ試料の作製を試み,最終的には保磁力メカニズムの解明を目指す.昨年度実施された研究において,Nd 被覆によって14kOe という著しい保磁力増大を示す試料の作製に成功した.しかし保磁力の到達値は最大16.5kOe であり,Dy フリー磁石としてはそれ程大きな値ではない.そこで今年度は,更なる保磁力増大を目指し,Nd2Fe14B 相の単磁区臨界サイズ(250 nm)以下でモデル界面をもつNd-Fe-B/Nd 薄膜の作製を試みた. この試料の構造と保磁力に対するNd2Fe14B 粒子サイズ依存性について検討した.
英文要約Nd-Fe-B magnets are useful permanent magnets utilized in many applications such as motors, HDD and mobile phones. Recently, they are used in motors of hybrid electric vehicles (HEV) which is one of the most promising application of Nd-Fe-B magnets. As high heat resistance and high coercivity are strongly required in HEVs, some amounts of Dy are added to Nd-Fe-B magnets. However, the natural abundance of Dy is quite low and producing countries are limited. Therefore, the development of Dy-free or Dy-less Nd-Fe-B sintered magnets with high coercivity is strongly demanded. In order to enhance the coercivity, grain refinement of microstructure in sintered magnets and the microstructural control at the interface between Nd2Fe14B and Nd-rich phases are important. Therefore, the following researches were carried out in this research. Section 2: Development of coercivity enhancement technique by controlling interface nanostructure. Subsection 2-2: Coercivity enhancement study by using model interface fabricated by sputtering process; In order to verify the coherent lattice-matching conjecture and to clarify the coercivity mechanism in sintered Nd-Fe-B magnets, it would be helpful to manipulate the interface between main and Nd-rich phases. We thus use the sputtering process to form such a model interface and to compare the coercivity values of the films with and without Nd overlayer, which is a simulated intergranular Nd-rich phase. In this year, we fabricated the Nd-Fe-B/Nd films with smaller grain sizes, in order to investigate the size dependence of the coercivity and its relation with the Nd coating. Films of Mo (20 nm)/Nd-Fe-B (5 ~ t(NFB) ~ 70 nm)/Nd (t(Nd) = 0, 60 nm)/Mo (10 nm) were deposited by using UHV sputtering system onto MgO(100) single-crystal substrates. As the Nd-Fe-B layer thickness t(NFB) was decreased from 70 nm to 5nm, the coercivity Hc exhibited a gradual increase behavior from 6.5 kOe to 16 kOe, and from 17.5 kOe to 26 kOe for the Nd-Fe-B and Nd-Fe-B/Nd films, respectively. It should be noted that the amount of Hc increase by the Nd coating was about 10 kOe irrespective of t(NFB) value. AFM observations showed that the average Nd-Fe-B particle size of the t(NFB) = 5 nm film is about 60 nm, which is much smaller than the critical size ( ~ 250 nm) for the single domain in the Nd2Fe14B phase. X-ray diffraction measurements showed an existence of NdOx phases, as reported in the previous films with larger grain size. These results therefore suggest that a proper interface state is extremely important to achieve high Hc not only in larger grain system but also in smaller particle one.
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