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論文

Composition dependence of the anomalous Nernst effect in Fe $_{4-x}$ Mn $_{x}$ N and Fe $_{4-y}$ Co $_{y}$ N films

Yin, W.*; 伊藤啓太*; 坪和優佑*; 辻川雅人*; 白井正文*; 梅津理恵*; 高梨弘毅

Journal of Magnetism and Magnetic Materials, 628, p.173157_1 - 173157_8, 2025/09

https://doi.org/10.1016/j.jmmm.2025.173157

被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

Fe $_{4}$ N exhibits a large anomalous Nernst effect (ANE), which motivates a systematic study of enhancing the anomalous Nernst coefficient (S $_{rm ANE}$ ) by modulating its electronic and magnetic structures. In this study, Mn and Co substitution effects for Fe in Fe $_{4}$ N on S $_{ANE}$ were investigated. Fe $_{4-x}$ Mn $_{x}$ N and Fe $_{4-y}$ Co $_{y}$ N films in wide ranges of x and y were grown epitaxially on MgO(001) and (LaAlO $_{3}$ ) $_{0.3}$ (Sr $_{2}$ TaAlO $_{6}$ ) $_{0.7}$ (001) substrates, respectively, using molecular beam epitaxy. The S $_{rm ANE}$ value of the Fe $_{4}$ N film is suppressed by substituting Fe with Mn or Co. By measuring the ANE, Seebeck effect, and anomalous Hall effect, the transverse thermoelectric conductivity ( $alpha_{xy}$ ) was evaluated. The composition dependence of S $_{ANE}$ was dominated by the change of $alpha_{xy}$ for both Fe $_{4-x}$ Mn $_{x}$ N and Fe $_{4-y}$ Co $_{y}$ N films. First-principles calculations were conducted for the transverse electric conductivity ( $sigma_{xy}$ ) and $alpha_{xy}$ of Fe $_{4}$ N and Fe $_{3.1}$ Co $_{0.9}$ N, and large $alpha_{xy}$ leading to large S $_{ANE}$ was predicted in Fe $_{3.1}$ Co $_{0.9}$ N.

論文

Strong low-energy rattling modes enabled liquid-like ultralow thermal conductivity in a well-ordered solid

Liu, P.-F.*; Li, X.*; Li, J.*; Zhu, J.*; Tong, Z.*; 古府麻衣子*; 楡井真実; Xu, J.*; Yin, W.*; Wang, F.*; et al.

National Science Review, 11(12), p.nwae216_1 - nwae216_10, 2024/12

https://doi.org/10.1093/nsr/nwae216

被引用回数：16 パーセンタイル：91.30(Multidisciplinary Sciences)

Crystalline solids exhibiting inherently low lattice thermal conductivity ( $kappa_{rm L}$ ) are of great importance in applications such as thermoelectrics and thermal barrier coatings. However, $kappa_{rm L}$ cannot be arbitrarily low and is limited by the minimum thermal conductivity related to phonon dispersions. In this work, we report the liquid-like thermal transport in a well-ordered crystalline CsAgTe, which exhibits an extremely low $kappa_{rm L}$ value of 0.18 Wm $^{-1}$ K $^{-1}$ . On the basis of first-principles calculations and inelastic neutron scattering measurements, we find that there are lots of low-lying optical phonon modes at 3.1 meV hosting the avoided-crossing behavior with acoustic phonons. These strongly localized modes are accompanied by weakly bound rattling Ag atoms with thermally induced large amplitudes of vibrations. Using the two-channel model, we demonstrate that coupling of the particle-like phonon modes and the heat-carrying wave-like phonons is essential for understanding the low $kappa_{rm L}$ , which is heavily deviated from the temperature dependence of the standard Peierls theory. In addition, our analysis indicates that the soft structural framework with liquid-like motions of the fluctuating Ag atoms is the underlying cause that leads to the suppression of the heat conduction in CsAgTe. These factors synergistically account for the ultralow $kappa_{rm L}$ value. Our results demonstrate that the liquid-like heat transfer could indeed exist in a well-ordered crystal.

論文

Enhancing mechanical properties of medium Mn steel by warm rolling based on laminated elemental segregation

Chen, H. F.*; Liu, B. X.*; 徐平光; Fang, W.*; Tong, H. C.*; Yin, F. X.*

Journal of Materials Research and Technology, 32, p.3060 - 3069, 2024/09

https://doi.org/10.1016/j.jmrt.2024.08.060

被引用回数：1 パーセンタイル：22.74(Materials Science, Multidisciplinary)

The hot-rolled microstructure of medium Mn steel has coarse grains and severe elemental segregation, resulting in low strength and plasticity. Constructing a multiphase structure, refining the microstructure, and regulating elemental segregation enhance the mechanical properties. In this study, liquid nitrogen treatment created a layered distribution of austenite and martensite. Warm rolling was then used to reduce layer thickness and refine grain structure. After liquid nitrogen and warm rolling treatments, the strength and plasticity of medium Mn steel increased to 1270 MPa and 23.3%, respectively, far exceeding the hot-rolled state (724 MPa, 12.8%). Warm rolling also triggers austenite reverted transformation (ART) and introduces high-density dislocations, further improving austenite stability. This strengthening effect is higher than that from intercritical annealing alone. Improved austenite stability delays the transformation induced plasticity (TRIP) effect, preventing brittle fracture and enhancing deformation coordination between layers, significantly increasing the plastic deformation capacity of medium Mn steel.

論文

Influence of interstitial carbon on bulk texture evolution of carbide-free high-entropy alloys during cold rolling using neutron diffraction

Fang, W.*; Liu, C.*; Zhang, J.*; 徐平光; Peng, T.*; Liu, B.*; 諸岡聡; Yin, F.*

Scripta Materialia, 249, p.116046_1 - 116046_6, 2024/08

https://doi.org/10.1016/j.scriptamat.2024.116046

被引用回数：4 パーセンタイル：65.10(Nanoscience & Nanotechnology)

The influence of interstitial carbon on the texture evolution of high-entropy alloys during cold rolling was investigated. To prevent carbide formation, elements with weak carbon affinity were carefully selected in the (FeMnCoNi) $_{96.5}$ C $_{3.5}$ alloy. Neutron diffraction, electron channeling contrast imaging, and electron backscatter diffraction were used to analyze the texture and microstructure evolution in alloys with and without carbon addition. Though their texture components are similar at the early stage of deformation, the Brass and Goss textures in the carbon-containing alloy at 50% cold rolling reduction are obviously higher than those in the carbon-free alloy, while Copper and S textures are lower. A large number of deformation twins induced in the carbon containing alloy is attributed as the significant reason for the texture differences. This work helps to understand the impact of interstitial carbon on the texture evolution of high-entropy alloys, providing valuable insights for microstructure and performance optimization.

論文

Phase transformation and equation of state in Ti-45Al alloy under high pressure

Li, X.*; Zhu, R.*; Xin, J.*; Luo, M.*; Shang, S.-L.*; Liu, Z.-K.*; Yin, C.*; 舟越賢一*; Dippenaar, R. J.*; 肥後祐司*; et al.

CALPHAD; Computer Coupling of Phase Diagrams and Thermochemistry, 84, p.102641_1 - 102641_6, 2024/03

https://doi.org/10.1016/j.calphad.2023.102641

被引用回数：0 パーセンタイル：0.00(Thermodynamics)

The phase transformations and pressure-volume dependencies of the Ti-45Al alloy with respect to pressure have been investigated by means of in-situ observation using multi anvil-type high-pressure devices and synchrotron radiation. Under hydrostatic compression from 0 to 10.1 GPa, about 2.3 vol. % of transforms continuously to 2. Lattice parameters as well as volume fractions of these two phases have been determined as a function of pressure. Bulk moduli estimated using Birch-Murnaghan's equation of state are 148 GPa for the phase, 138 GPa for the 2 phase, and 149 GPa for their two-phase mixture of Ti-45Al alloy. First-principles have also applied to investigate bulk moduli of two single phases, and the deviation between calculations and measurements is discussed and attributed to mainly phase transformation. The presently study provides useful insights into thermodynamics of 2 and phases under high pressure.

論文

The BCC FCC hierarchical martensite transformation under dynamic impact in FeMnAlNiTi alloy

Li, C.*; Fang, W.*; Yu, H. Y.*; Peng, T.*; Yao, Z. T.*; Liu, W. G.*; Zhang, X.*; 徐平光; Yin, F.*

Materials Science & Engineering A, 892, p.146096_1 - 146096_11, 2024/02

https://doi.org/10.1016/j.msea.2024.146096

被引用回数：6 パーセンタイル：78.45(Nanoscience & Nanotechnology)

The quasi-static superelastic responses and hierarchical martensite transformation from body-centered cubic (BCC) to face-centered cubic (FCC) under dynamic impact in Fe $_{42}$ Mn $_{34}$ Al $_{15}$ Ni $_{7.5}$ Ti $_{1.5}$ alloys were investigated. Polycrystalline and oligocrystalline alloys were produced through solution heat treatment and cyclic heat treatment processes, respectively. The results show the volume fraction of residual martensite for oligocrystalline alloys is lower, which exhibits better superelastic responses compared with polycrystalline alloys. Dynamic impact tests indicate that, despite the weakening of the grain boundary strengthening effect, the ultimate strength of the oligocrystalline alloys closely matches that of the polycrystalline alloys under dynamic impact. The martensite transformation of the FeMnAlNiTi alloy is characterized as hierarchical under dynamic impact, and increasing strain rates and grain sizes can enhance the BCC FCC martensite transformation, resulting in higher martensite phase fractions for oligocrystalline alloys. The increase in ultimate strength is attributed to the dynamic Hall-Petch effect introduced by more martensite phase interfaces under dynamic impact.

論文

Stacking fault driven phase transformation in CrCoNi medium entropy alloy

He, H.*; Naeem, M.*; Zhang, F.*; Zhao, Y.*; Harjo, S.; 川崎卓郎; Wang, B.*; Wu, X.*; Lan, S.*; Wu, Z.*; et al.

Nano Letters, 21(3), p.1419 - 1426, 2021/02

https://doi.org/10.1021/acs.nanolett.0c04244

被引用回数：77 パーセンタイル：96.40(Chemistry, Multidisciplinary)

In CrCoNi, a so-called medium-entropy alloy, an fcc-to-hcp phase transformation has long been anticipated. Here, we report an in situ loading study with neutron diffraction, which revealed a bulk fcc-to-hcp phase transformation in CrCoNi at 15 K under tensile loading. By correlating deformation characteristics of the fcc phase with the development of the hcp phase, it is shown that the nucleation of the hcp phase was triggered by intrinsic stacking faults. The confirmation of a bulk phase transformation adds to the myriads of deformation mechanisms available in CrCoNi, which together underpin the unusually large ductility at low temperatures.

論文

Coexistence of ferromagnetic and stripe-type antiferromagnetic spin fluctuations in YFe $_{2}$ Ge $_{2}$

Wo, H.*; Wang, Q.*; Shen, Y.*; Zhang, X.*; Hao, Y.*; Feng, Y.*; Shen, S.*; He, Z.*; Pan, B.*; Wang, W.*; et al.

Physical Review Letters, 122(21), p.217003_1 - 217003_5, 2019/05

https://doi.org/10.1103/PhysRevLett.122.217003

被引用回数：7 パーセンタイル：45.84(Physics, Multidisciplinary)

We report neutron scattering measurements of single-crystalline YFe $_{2}$ Ge $_{2}$ in the normal state, which has the same crystal structure as the 122 family of iron pnictide superconductors. YFe $_{2}$ Ge $_{2}$ does not exhibit long-range magnetic order but exhibits strong spin fluctuations. Like the iron pnictides, YFe $_{2}$ Ge $_{2}$ displays anisotropic stripe-type antiferromagnetic spin fluctuations at (). More interesting, however, is the observation of strong spin fluctuations at the in-plane ferromagnetic wave vector (). These ferromagnetic spin fluctuations are isotropic in the () plane, whose intensity exceeds that of stripe spin fluctuations. Both the ferromagnetic and stripe spin fluctuations remain gapless down to the lowest measured energies. Our results naturally explain the absence of magnetic order in YFe $_{2}$ Ge $_{2}$ and also imply that the ferromagnetic correlations may be a key ingredient for iron-based materials.

論文

Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe $_{2-x}$ T $_{x}$ As $_{2}$ ( = Co,Ni)

Tam, D. M.*; Song, Y.*; Man, H.*; Cheung, S. C.*; Yin, Z.*; Lu, X.*; Wang, W.*; Frandsen, B. A.*; Liu, L.*; Gong, Z.*; et al.

Physical Review B, 95(6), p.060505_1 - 060505_6, 2017/02

https://doi.org/10.1103/PhysRevB.95.060505

被引用回数：24 パーセンタイル：67.56(Materials Science, Multidisciplinary)

We use neutron diffraction and muon spin relaxation to study the effect of in-plane uniaxial pressure on the antiferromagnetic (AF) orthorhombic phase in BaFe $_{2-x}$ T $_{x}$ As $_{2}$ and its Co- and Ni-substituted members near optimal superconductivity. In the low-temperature AF ordered state, uniaxial pressure necessary to detwin the orthorhombic crystals also increases the magnetic ordered moment, reaching an 11% increase under 40 MPa for BaFe $_{1.9}$ Co $_{0.1}$ As, and a 15% increase for BaFe $_{1.915}$ Ni $_{0.085}$ As. We also observe an increase of the AF ordering temperature () of about 0.25 K/MPa in all compounds, consistent with density functional theory calculations that reveal better Fermi surface nesting for itinerant electrons under uniaxial pressure. The doping dependence of the magnetic ordered moment is captured by combining dynamical mean field theory with density functional theory, suggesting that the pressure-induced moment increase near optimal superconductivity is closely related to quantum fluctuations and the nearby electronic nematic phase.

論文

Spin excitations in optimally P-doped BaFe(As $_{0.7}$ P $_{0.3}$ ) superconductor

Hu, D.*; Yin, Z.*; Zhang, W.*; Ewings, R. A.*; 池内和彦*; 中村充孝; Roessli, B.*; Wei, Y.*; Zhao, L.*; Chen, G.*; et al.

Physical Review B, 94(9), p.094504_1 - 094504_7, 2016/09

AA2016-0252.pdf:2.18MB

https://doi.org/10.1103/PhysRevB.94.094504

被引用回数：21 パーセンタイル：63.42(Materials Science, Multidisciplinary)

最適Pドープされた超伝導体BaFe(As $_{0.7}$ P $_{0.3}$ ) (T=30K)におけるスピン励起の温度及びエネルギー依存性が非弾性中性子散乱実験を使って調べられた。我々の実験結果は密度汎関数理論や動的平均場理論で予想される計算結果と矛盾しておらず、BaFe(As $_{0.7}$ P $_{0.3}$ )における平均プニクトゲン高さの減少が、電子相関の強さを弱め、磁気励起の有効バンド幅の増加に寄与することを示唆している。

論文

Implications of NbTi short-sample test results and analysis for the ITER Poloidal Field Conductor Insert (PFCI)

Zanino, R.*; Bagnasco, M.*; Baker, W.*; Bellina, F.*; Bruzzone, P.*; della Corte, A.*; Ilyin, Y.*; Martovetsky, N.*; Mitchell, N.*; Muzzi, L.*; et al.

IEEE Transactions on Applied Superconductivity, 16(2), p.886 - 889, 2006/06

https://doi.org/10.1109/TASC.2006.873318

被引用回数：7 パーセンタイル：40.08(Engineering, Electrical & Electronic)

那珂核融合研究所においてITERポロイダル磁場コイル導体インサート(PFCI)の実験が予定されている。このため、PFCIの適切な実験プログラムを作成することを目的として、NbTi短尺導体サンプル実験から得られた結果の解析を行った。特に、次の項目について検討を行った;(1)巻線内の導体ジョイントがクエンチする前に導体自身の分流開始温度Tcsを測定できる可能性に関する検討。(2)解析コードMithrandirを用いて短尺導体サンプルの実験結果を解析し、いわゆる突然の又は早期のクエンチの可能性に関する検討。(3)PFCI実験における熱量法によるACロス測定の可能性。検討の結果、Tcs及びACロスの測定は可能であることがわかった。しかし、突然のクエンチについては今後のこれらの検討が必要である。