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Rare-earth magnets are mainly composed of 3d transition metals (T) and rare-earth metals (R). The former yield large magnetization, while the latter are a source of strong magnetocrystalline anisotropy (at low temperature). Strong magnet compounds, such as Nd2Fe14B and Sm2Fe17N3, contain a light element (X) as a third element. We will discuss the role of the X element in the magnetism of R-T-X systems. First-principles calculations [1] clarify that the magnetic moment depends sensitively on X as a consequence of orbital hybridization between X-2p and T-3d. Crystal-field coefficients at the R sites are also affected by X. This suggests that magnetocrystalline anisotropy can be controllable by additive elements. We will also present a combined first-principles and classical spin model analysis of magnetocrystalline anisotropy at finite temperature [2,3,4].

[1] Y. Harashima et al., Phys. Rev. B 92, 184426 (2015).
[2] M. Matsumoto et al., J. Appl. Phys. 119, 213901 (2016).
[3] Y. Toga et al., Phys. Rev. B 94, 174433 (2016).
[4] T. Fukazawa et al., arXiv:1612.04478.

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