ホーム > 研究活動 > 口頭発表(2013) > Nd-oxides as intergranular phases of Nd-Fe-B

研究活動

Nd-oxides as intergranular phases of Nd-Fe-B

ISAMMA2013

Takuya Yoshioka ( Tohoku univ )
Hiroki Tsuchiura ( Tohoku univ )
Pavel Novak ( ASCR )

Abstract

Because of the recent developments of renewable and sustainable technology, there has been emerging interest in improving the coercivity of Nd-Fe-B permanent magnets, and in revealing its mechanism.
Several recent experimental studies have shown that local structures around the grain boundaries of sintered Nd-Fe-B magnets significantly affect their coercivity.
Theoretically, we have estimated the crystal field of Nd ions around the surface of the crystalline Nd2Fe14B based on first-principles calculations, and found that the Nd ions exposed on the (001) surface exhibit c-plane magnetic anisotropy [1,2], resulting in a reduction of coercivity of a single Nd2Fe14B grain by half of the anisotropy field HK [3].
The next question we have to study is (i) whether such coercivity reduction mechanism can be realized in more realistic interfacial structures of Nd-Fe-B sintered magnets, and (ii) how Nd2Fe14B grains magnetically coupled each other through grain boundaries.
In particular, magnetic properties of the grain boundaries, that is, whether they show magnetism or not, is a crucial issue to understand the coercivity mechanism of Nd-Fe-B magnets.
It is well known that Nd oxides are found in the so-called Nd-rich phases at the grain boundaries.
Thus in this study, we investigate the magnetic structures and magnetic anisotropy of NdO2 and Nd2O3 using first-principles calculations.
We have confirmed that a purely antiferromagnetic (AF) structure occurs in the so-called C-type structure of Nd2O3, as shown in the figure.
For NdO2, by contrast, we can see the residual density of states at the Fermi energy, which implies that a simple AF state is not favored in this system.
We will examine the relative stabilities of various kinds of magnetic states for NdO2.
We also discuss the magnetic properties of thin-layered systems of these materials.
[1] H. Moriya, H. Tsuchiura, and A. Sakuma, J. Appl. Phys. 105, 07A740 (2009).
[2] S. Tanaka, H. Moriya, H. Tsuchiura, A. Sakuma, M. Divis, and P. Novak, J. Appl. Phys. 109, 07A702 (2011).
[3] C. Mitsumata, H. Tsuchiura, and A. Sakuma, Appl. Phys. Express 4, 113002 (2011).


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