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SmCo12磁能积大, 是当前备受关注的一种极具应用潜力的高温永磁体, 但该体系普遍存在的ThMn12型晶体结构面临严峻的稳定性挑战, 严重制约其实际工程应用. 探索兼具稳定性和优良磁性能的SmCo12新结构是突破这一瓶颈的关键. 本文采用局域粒子群优化算法结合第一性原理计算, 系统探索了SmCo12体系的亚稳相. 理论计算发现了一种六方相结构(空间群 $ P\overline{3}1m $), 其形成能较传统ThMn12型SmCo12低90 meV/atom. 声子谱和分子动力学模拟也证实其具有动力学和热力学稳定性. 此外, 理论预测六方相SmCo12结构表现出非常优异的磁性能, 最大磁能积、各向异性场, 以及居里温度可达54.56 MGOe (1 GOe = 7.9577×10-3 J/m3), 15.01 MA/m和1180 K. 本文新发现的六方相SmCo12为解决ThMn12型结构的稳定性难题提供了新方向.SmCo12, with its large magnetic energy product, is a highly promising high-temperature permanent magnet that has attracted significant attention. However, the widely existing ThMn12-type crystal structure in this system faces serious stability problem, which significantly hinders its practical engineering applications. Exploring a novel SmCo12 structure that combines stability and excellent magnetic properties is crucial for breaking through this bottleneck. In this study, the metastable phases of the SmCo12 system are systematically investigated by using a local particle swarm optimization algorithm combined with first-principles calculations. The theoretical calculations reveal a hexagonal phase structure (space group $ P\overline{3}1m $) with a formation energy 90 meV/atom lower than that of the conventional ThMn12-type SmCo12. Its phonon spectrum shows no imaginary frequencies and its structure remains stable during Nosé-Hoover thermostat simulations at 1200 K, confirming its dynamic stability and thermodynamic stability. The electronic structure reveals that this structure exhibits metallic characteristics, with a total magnetic moment of as high as 21.81 μB/f.u. and a magnetocrystalline anisotropy constant of up to 11.10 MJ/m3, significantly exceeding similar high-cobalt-content Sm-Co systems. Furthermore, theoretical predictions indicate that the hexagonal phase SmCo12 structure exhibits exceptionally outstanding magnetic properties, with maximum energy product, anisotropy field, and Curie temperature reaching 54.56 MGOe, 15.01 MA/m, and 1180 K, respectively. The newly discovered hexagonal SmCo12 phase provides a novel direction for solving the stability problem of the ThMn12-type structure.
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Keywords:
- structure prediction /
- first principles calculations /
- high Curie temperature /
- rare earth permanent magnets
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Space Group Enthalpy/(eV·atom–1) Lattice parameters/Å Wyckoff position Crystal system $ P4 mm $ (No.99) –6.52 a = b = 4.00, c = 10.65
α = β = γ = 90°Sm: $ 1a $
Co: $1 {a}_{i} $; $1 {b}_{i} $; $ 2{c}_{i} $ (i = 1, 2, 3)Tetragonal $ I4/mmm $ (No.139) –6.67 a = b = 8.89, c = 4.087
α = β = γ = 90°Sm: $ 2a $
Co: $8 f $; $8 i $; $8 j $Tetragonal $ P\overline{3}1 m $ (No.162) –6.76 a = b = 4.20, c = 10.93
α = β = 90°, γ = 120°Sm: $1 b $
Co: $6 {k}_{1} $; $6 {k}_{2} $Hexagonal $ P4/mmm $ (No.123) –6.79 a = b = 3.54, c = 12.13
α = β = γ = 90°Sm: $1 a $
Co: $2 {h}_{i} $ (i = 1, 2); $ 4i $; $ 2h $; $2 e $Tetragonal 
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Space
groupVolume
/Å3Formation energy
(meV/atom)Bulk
module
/GPa$ {E}_{\mathrm{f}\mathrm{o}\mathrm{r}\mathrm{m}} $ $ {E}_{\mathrm{f}\mathrm{o}\mathrm{r}\mathrm{m}}^{\mathrm{S}\mathrm{m}\mathrm{C}{\mathrm{o}}_{5}} $ $ {E}_{\mathrm{f}\mathrm{o}\mathrm{r}\mathrm{m}}^{\mathrm{S}{\mathrm{m}}_{2}\mathrm{C}{\mathrm{o}}_{17}} $ $ P4 mm $(No.99) 173.22 0 63 67 111.00 $ I4/mmm $(No.139) 323.12 –47 16 21 145.50 $ P\overline{3}1 m $(No.162) 172.16 –137 –74 –69 131.99 $ P4/mmm $(No.123) 161.37 –167 –104 –99 154.33
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Method Atom s p d $ {m}_{i/\mu_\mathrm{B}} $ $ {k}_{i} $/meV OpenMX Co 6$ {k}_{1} $ –0.01 –0.08 1.74 1.66 0.19 Co 6$ {k}_{2} $ 0.0 –0.06 1.84 1.76 0.46 Sm 1$ b $ –0.01 –0.04 1.29 1.25 –11.97 VASP Co 6$ {k}_{1} $ –0.02 –0.05 1.67 1.60 0.57 Co 6$ {k}_{2} $ –0.01 –0.04 1.57 1.52 0.4 Sm 1$ b $ –0.01 –0.01 –0.21 –0.23 –8.93
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Atoms Occ. $ {m}_{i}^{s}/{\mu }_{{\mathrm{B}}} $ $ {m}_{i}^{\mathrm{o}\mathrm{r}\mathrm{b}\mathrm{i}\mathrm{t}}/{\mu }_{{\mathrm{B}}} $ $ {m}_{i}/{\mu }_{{\mathrm{B}}} $ Co 6$ {k}_{1} $ 1.66 0.07 1.73 Co 6$ {k}_{2} $ 1.76 0.08 1.84 Sm 1$ b $ 1.25 0.02 1.27
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Space Group $ {m}^{\mathrm{t}\mathrm{o}\mathrm{t}}/ $($ {\mathrm{\mu }}_{\mathrm{B}} $·f.u.–1) $ {M}_{\mathrm{s}}/ $(MA·m–1) $ (\mathrm{B}\mathrm{H}{)}_{\mathrm{m}\mathrm{a}\mathrm{x}}/ $MGOe $ {H}_{\mathrm{a}}/ $(MA·m–1) $ {T}_{\mathrm{C}}/ $K $ P\overline{3}1 m $ (No.162) SmCo12 21.81 1.17 54.56 15.01 1180 ThMn12-type SmCo12 * 21.90 1.26 62.38 8.70 1150 ThMn12-type SmCo12 [15,38,40,41] 17.4 1.0 39.60 3.91 1300 ThMn12-type SmFe12 [38,41,44] 25.7 1.30 76.0 9.55 554 ThMn12-type Sm(Fe0.8Co0.2)12 [15,43] 24.5 1.35 80 9.55 1100 注: *present work.
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[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45]
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