ホーム > 研究活動 > 口頭発表(2014) > Computational approaches for understanding the role of grain boundary phase on magneticproperty of NdFeB hard magnet

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Computational approaches for understanding the role of grain boundary phase on magneticproperty of NdFeB hard magnet

59th Annual conference on Magnetism and Magnetic Materials (MMM2014)

Toshiyuki Koyama, Taichi Abe, Yuhki Tsukada and Yoshinao Kobayashi

概要/Abstract

It is widely known that Nd-rich amorphous phase forms at the grain boundary (GB) region inNd2Fe14B polycrystalline microstructure during optimization annealing, and the coercive forcedepends crucially on the Nd concentration in the amorphous GB phase. In this study, we attemptfor understanding the thermodynamic nature of Nd-rich amorphous phase based on the Calphadmethod and phase-field method, and calculate the effect of Nd-rich amorphous phase on thecoercive force of material by micromagnetics simulation. Results obtained are as follows: (1) Themetastable Nd-Fe-B ternary phase diagram was calculated based on the conventional Calphadapproach, where liquid phase and Nd-Fe-B ternary compounds including Nd2Fe14B phase areconsidered. The metastable phase diagram reveals that Nd concentration in the amorphous GBphase, which is measured in experiment, is reasonably explained if we assume the amorphousphase to be a liquid one. (2) The Nd concentration in amorphous GB phase was analyzed based onthe modified grain-boundary-phase (GBP) model. The phenomenological segregation behavior ofmicro-alloying elements at grain boundary region has been theoretically explained based on theGBP model. We modified the GBP model by considering the composition gradient energy throughthe phase-field methodology, then the extended GBP model was applied to the Nd segregationbehavior in Nd2Fe14B hard magnet. Important result is that the Nd segregation is cruciallydependent on the tiny change of average composition of Nd. (3) The magnetic property ofNd2Fe14B polycrystalline microstructure including GB phase was calculated by the image-basedmicromagnetics simulation based on the Landau–Lifshitz–Gilbert equation, where the maximummagnetization of GB phase was systematically changed. The behavior of magnetic domainboundary migration during magnetization and the value of coercive force depend on the magneticproperty of GB phase, i.e. the coercive force increases with decreasing maximum magnetization ofGB phase.



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