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A mixed-valence model for Ce2Fe14B compounds

64th Annual Conference on Magnetism and Magnetic Materials

Hikaru Tabata(Tohoku University),Hiroki Tsuchiura(Tohoku University), TakuyaYoshioka(Tohoku University)

Abstract

Because of the recent intensive use of Nd and Dy for high performance Nd-Fe-B permanent magnets,there is an urgent need to develop novel, economically attractive magnetic materials. Ce-based, or atleast Ce-sub- stituted permanent magnets, will be of particular interest because Ce is the mostabundant rare-earth element. It is well known, however, that Ce-based magnetic materials such asCe2Fe14B usually do not have high magnetocrys- talline anisotropy as a consequence of the lesstightly-bound 4f electronic clouds in those systems. Theoretically, much less is known about the 4felectronic states of Ce ions in the Ce2Fe14B because the modern first-prin- ciples calculationstechniques still have problems to treat them. Thus in this study, we propose an alternative theoreticalmodel to understand how the 4f electrons behave, and how these materials loses magnetocrystallineanisotropy. This model is essentially a cluster-type model which consists of Ce 4f orbital degrees offreedom and several surrounding ligand orbitals. The hybridization amplitude between the 4f and ligandorbitals is given as a parameter V in this model. This model reduces to the localized spin model in a limitwith V=0, which has been widely used for rare-earth based permanent magnets [1]. Figure 1 shows thetemperature dependences of the magnetic anisotropy constant K1 obtained by using the present model.We find that the experimental data [2] can be well described at any temperature, when we takeV=1100K. The localized spin model extremely overestimates K1, as also shown in Fig. 1. The Vdependences of K1 and the 4f electronic density N4f are shown in Fig. 2. We can see that N4f firstrapidly decreases but becomes almost independent with increasing V.
However, K1 decreasesmonotonically even when N4f is nearly constant around 0.5. This results may correspond to the weakmagnetic anisotropy of Ce2Fe14B.






研究活動

文部科学省

文部科学省
元素戦略プロジェクト(活動紹介)
NIMS磁石パートナーシップ

元素戦略拠点

触媒・電池元素戦略拠点
触媒・電池元素戦略研究拠点 (京都大学)
東工大元素戦略拠点
東工大元素戦略拠点 (東京工業大学)
構造材料元素戦略研究拠点
構造材料元素戦略研究拠点 (京都大学)
高効率モーター用磁性材料技術研究組合
高効率モーター用 磁性材料技術研究組合