磁石材料微細構造最適化に向けて <<SPring-8との連携>> Sept. 2, 2014 合田 義弘 Y. Gohda Department of Materials Science and Engineering Tokyo Institute of Technology 1 /24 Acknowledgments In collaboration with: Z. Torbatian (ESICMM-UT) D. Hirai (ESICMM-UT) Y. Tatetsu (ESICMM-UT) S. Tsuneyuki (UT) H. Misawa (UT) T. Ozaki (UT) T. Nakamura Sept. 2, 2014 2 /24 (JASRI/Spring-8) Y. Gohda contents microstructures of magnets XMCD in SPring-8 First-principles calculations of microstructure interfaces Toward calculations of interface magnetic anisotropy Method for calculations of site/orbital decomposition Strain effects on anisotropy in Y2Fe14B system Summary Sept. 2, 2014 3 /24 Y. Gohda wind turbine permanent magnets permanent magnet synchronous motor used at high temperature Large magnetic moment High Curie temperature High coercivity Sept. 2, 2014 4 /24 Y. Gohda figure of merit: BHmax Sept. 2, 2014 Hc: coercive field 5 /24 J.M.D. Coey, IEEE Trans. Magn. 47, 4671 (2011). Y. Gohda magnetic couplings in Nd2Fe14B Nd 4f 3d-5d hybridization Hund coupling Nd 5d Fe 3d Density of states [arb. unit] up Ndf 4f j2 Fe 3d Ndf 5d 0 Ndf 5d Fej2 3d down −10 −8 Ndf 4f −6 −4 −2 0 2 4 6 8 Energy relative to εF [eV] a=8.76Å, c=12.11Å, μ=36.9μB/fu: DFT+U(6eV) w/o SOC Sept. 2, 2014 a=8.79Å, c=12.18Å μ=37.3μB/fu: experiment 6 /24 [J.M.D. Coey, 2009] Y. Gohda Nd-Fe-B sintered magnet @ 1000 ℃ B. Hallemans et al., J. Phase Equilibria (1995). W.F. Li et al., Acta Mater. (2011). Nd2Fe14B ≈5 μm main phase: micrograin of Nd2Fe14B grain-boundary phase: amorphous Nd-Fe alloy sub-phase: Nd-rich phases including oxides formed as the final point of solidification Sept. 2, 2014 7 /24 Y. Gohda supercomputer「京」 HPCIシステム一般利用 (hp120086) 「新磁石材料探査とその保磁力発現機構の解明」 Sept. 2, 2014 第一原理計算とマイクロマグネティクスシミュレーションを組み 合わせたマルチスケール解析 Y. Gohda 8 /24 微細構造の丸ごとシミュレーション（富士通・NIMS） SW model Considering a magneto-static interaction Non Magnetic layers(NML) at GBs Introduction of SMLs at GBs 富士通 プレスリリース (2013) Soft Magnetic layers(SML) at GBs 系のサイズ：サブμm Including initial reverse domain Soft Magnetic layers at GBs and initial reverse Domain 磁壁幅：∼5 nm 京による超並列計算：1 nm程度のグリッド幅 -> 磁壁幅を考慮に入れたシミュレーション Sept. 2, 2014 9 /24 Y. Gohda contents microstructures of magnets XMCD in SPring-8 First-principles calculations of microstructure interfaces Toward calculations of interface magnetic anisotropy Method for calculations of site/orbital decomposition Strain effects on anisotropy in Y2Fe14B system Summary Sept. 2, 2014 10/24 Y. Gohda Evaluation of mGB w/o knowledge of GB details To obtain mXMCD by sum-rule analysis, the number of 3d holes is needed. First-principles calculations Sept. 2, 2014 12 /24 Y. Gohda Number of Fe 3d electrons Fe 3d in Nd2Fe14B Fe 3d in Y2Fe14B up+down 6.67 6.60 up-down 2.60 2.47 Mulliken population analysis mGB = 1.4 μB -> GB phase identified as ferromagnetic Sept. 2, 2014 13/24 Y. Gohda Further collaboration 第一原理計算による実験対象とする系の同定 計算結果に応じたモデル試料の作成 放射光等による計測 計測結果に応じた第一原理計算による理論解析 微細構造の副相および主相/副相界面 Sept. 2, 2014 14/24 Y. Gohda contents microstructures of magnets XMCD in SPring-8 First-principles calculations of microstructure interfaces Toward calculations of interface magnetic anisotropy Method for calculations of site/orbital decomposition Strain effects on anisotropy in Y2Fe14B system Summary Sept. 2, 2014 15/24 Y. Gohda role of oxygen Sepehri-Amin et al., Acta Mater. 60, 819 (2012). non-equilibrium NdOx phase nucleation of magnetic domains at main-phase/triple-junction interfaces? Sept. 2, 2014 16 /24 Y. Gohda Nd4O 0 Mixing energy [eV] Nd −0.5 octahedral −1 tetrahedral Nd O Nd4O −1.5 −2 −2.5 −3 mixing entropy ≈ 0.02 eV (300 K) 0 0.1 0.2 0.3 NdO 0.4 0.5 Oxygen concentration Oxygen at tetrahedral sites Density of states [arb. units] up Nd f Nd f O 0 O Nd f down Nd: [Xe](6s5d)2.54f3 −10 −5 0 5 10 Energy relative to εF [eV] a=5.44 Å <- agrees with experiment Sept. 2, 2014 17/24 Y. Gohda Nd2Fe14B(001)√2×√2-Nd4O(001)√5×√5 Fe 2 3d μ=2.64μB DOS [1/eV] 1 0 -1 -2 -8 -6 -4 -2 0 2 4 6 8 6 8 Energy [eV] 2 μ=2.44μB DOS [1/eV] 1 0 -1 -2 -8 -6 -4 -2 0 2 4 Energy [eV] anisotropy at the interface? Sept. 2, 2014 18/24 Y. Gohda contents microstructures of magnets XMCD in SPring-8 First-principles calculations of microstructure interfaces Toward calculations of interface magnetic anisotropy Method for calculations of site/orbital decomposition Strain effects on anisotropy in Y2Fe14B system Summary Sept. 2, 2014 19/24 Y. Gohda strain effect Y2Fe14B YFe3 MAE (MJ/m3) . 2.0 . . . 0.0 . . 0.97 . . 1.0 0.97 1.0 1.0 . c/c0 a/a0 1.03 Y: [Ar+3d10]4s24p65s24d1 Fe: [Ne]3s23p64s23d6 3d-5d hybridization Nd 5d Fe 3d Sept. 2, 2014 Y2Fe14B 20/24 Y. Gohda MAE expressed by perturbation scheme Sept. 2, 2014 21/24 Y. Gohda anisotropy decomposition Y2Fe14B perturbation self-consistent equilibrium 4.0 meV (0.69 MJ/m3) 2.6 meV (0.45 MJ/m3) compressed 13.4 meV (2.58 MJ/m3) 11.2 meV (2.16 MJ/m3) 1MJ=6.24151x1024eV Sept. 2, 2014 22/24 Y. Gohda LDOS at the Fe j2 site (b) Y †* k2 k2 j1 k2 k1 k1 j2 j1 k2 k2 Y *† Z. Torbatian, T. Ozaki, S. Tsuneyuki, & Y. Gohda, Appl. Phys. Lett. (2014). Sept. 2, 2014 23/24 Y. Gohda summary microstructures of magnets XMCD in SPring-8 First-principles calculations of microstructure interfaces Toward calculations of interface magnetic anisotropy Method for calculations of site/orbital decomposition Strain effects on anisotropy in Y2Fe14B system Sept. 2, 2014 24/24 Y. Gohda
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