ホーム > 研究活動 > 口頭発表(2015) > Electronic theory for the magnetic properties of Nd2Fe14B compounds

研究活動

Electronic theory for the magnetic properties of Nd2Fe14B compounds

20th International Conference on Magnetism (ICM2015)

H. Tsuchiura, T. Yoshioka, P. Novák

概要/Abstract

In view the energy-saving and renewable technology, theoretical understanding of the coercivity mechanisms of Nd-Fe-B is urgently needed. It has been widely accepted that the large magnetic anisotropic energy due to the Nd ions is the dominant factor of the coercivity of Nd-Fe-B magnets. For deeper understanding of the mechanism, it is necessary to study the magnetic anisotropy due to the Nd ions from the viewpoint of crystal field theory. Several recent experimental studies have revealed that local atomic structures around the grain boundaries of sintered Nd-Fe-B magnets significantly affect their coercivity [1]. Theoretically, we have found that the crystal field parameters (CFP) A20 of Nd ions can be negative, implying the local in-plane anisotropy, if they are exposed on the (001) surface of the crystalline Nd2Fe14B [2]. We have also reported that such surface anisotropy anomaly may cause coercivity reduction of a single Nd2Fe14B particle by half of the anisotropy field HK, based on a simple micromagnetic-type simulation [3].In this talk, first we show the physical origin of the anomalous surface anisotropy by using newly developed CFP calculation technique, the so-called Wannierization method [4]. We find that the 4f clouds in Nd2Fe14B system are usually lie within the c-plane, but extend along the c- axis direction in the surface Nd ions. We also show the results of higher-order CFPs based on the Wannierization method, and discuss the spin-reorientation phenomena and coercivity of a single Nd2Fe14B particle.[1] H. Sepehri-Amin, T. Ohkubo, T. Shima, and K. Hono, Acta Mater. 60, 819 (2012) [2] H. Moriya, H. Tsuchiura, and A. Sakuma, J. Appl. Phys. 105, 07A740 (2009)[3] C. Mitsumata, H. Tsuchiura, and A. Sakuma, Appl. Phys. Exp. 4, 113002 (2011) [4] P. Novák, K. Knížek, and J. Kuneš, Phys. Rev. B 87, 205139 (2013)



研究活動

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