(ESICMM-G8 Symposium on Next Generation Permanent Magnets, Tsukuba, 2015)
First-principles approach to new rare-earth-lean permanent magnet compounds


Takashi Miyake

AIST, Tsukuba, Japan, and ESICMM, NIMS, Tsukuba, Japan

Abstract:

  The ThMn12-type rare-earth magnetic compounds (1:12 systems) are potential high-performance permanent magnets. Among them, NdFe11TiN [1] is known for large magnetization, although the value is smaller than that of Nd2Fe14B and Sm2Fe17N3. One of the advantages of the 1:12 systems is low content of rare-earth elements, which motivates us to study the systems for future rare-earth-lean permanent magnet compounds. In the present work, we study NdFe11TiN and related compounds theoretically [2,3]. The calculations are based on density functional theory in the generalized gradient approximation, with the open-core treatment for the Nd-4f orbitals. We found that a titanium atom reduces the magnetic moment by about 5 μB. It is substantially larger than the local magnetic moment at the substituted iron site, which can be explained from Friedel’s sum rule. Interstitial nitrogenation, on the other hand, enhances magnetization as a consequence of hybridization between the Fe-d and N-p orbitals. Nitrogenation also induces bonding charge between the N and Nd atoms. It results in significant enhancement of the crystal-electric-field parameter A20 ＜r2＞, suggesting strong uniaxial magnetic anisotropy. These results indicate that NdFe12N [4] would be a good candidate for a strong permanent magnet compound.
Figure 1. Crystal structure of NdFe11TiN
References:
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[2] T.Miyake, K.Terakura, Y.Harashima, H.Kino, and S.Ishibashi, J. Phys. Soc. Jpn. 83, 043702 (2014).
[3] Y.Harashima, K.Terakura, Y.Harashima, H.Kino, S.Ishibashi, and T. Miyake, JPS Conf. Proc. 5, 011021 (2015).
[4] Y. Hirayama, Y.K. Takahashi, S. Hirosawa, K. Hono, Scripta Mater. 95, 70 (2015).