Ali Shafiei
The compressive mechanical behavior of a dual phase cobalt alloy (Al$_{14}$Co$_{41}$Cr$_{16}$Fe$_{11}$Ni$_{18}$) is reported in this communication. An uncommon triple yielding phenomenon is observed in the as-cast condition. Microstructural studies suggest that the observed behavior may be due to a stress/strain-induced martensitic phase transformation.
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Designing cobalt-free face-centered cubic high-entropy alloys: A strategy using d-orbital energy level
针对含钴高熵合金不适用于核应用的问题，提出利用d轨道能级等六个参数设计无钴面心立方高熵合金，并通过实验验证，发现d轨道能级是决定相稳定性和力学性能的关键因素。
We screened six cobalt-based 18-VEC systems CoVSi, CoNbSi, CoTaSi (Si-group) and CoVGe, CoNbGe, CoTaGe (Ge-group) by the first-principles approach, with the motivation of stabilizing these orthorhombic phases into the cubic symmetry -- favorable for thermoelectrics. Remarkably, it was found that the Ge-group is energetically more favorable in the cubic symmetry than the hitherto orthorhombic phase. We account the cubic ground state of the Si-group to the interplay of internal pressure and covalent interactions. The principle of covalent interactions will provide an insight and could be vital i…
Data-driven body-centered cubic phase prediction in cobalt free high-entropy alloys
本文利用机器学习和数据增强技术，通过六个半经验参数预测无钴高熵合金的体心立方相稳定性，准确率达84%。
Substituting the main group element in cobalt - iron based Heusler alloys: Co$_2$FeAl$_{1-x}$Si$_x$
本文报道了Heusler化合物Co $_2$ FeAl $_{1-x}$ Si $_x$的电子结构计算。特别强调了主族元素在该化合物中的作用。Al被Si取代导致价电子数随着Si含量的增加而增加，并且可以被视为电子掺杂。自洽的电子结构计算进行了调查的结果，电子掺杂的磁性。发现系列化合物Co $_2$ FeAl $_{1-x}$ Si $_x$具有半金属铁磁性，其磁矩符合Slater Pauling规则。结果表明，电子掺杂稳定的间隙在少数状态$x=0.5$。
Despite the potential advantages of information storage in antiferromagnetically coupled materials, it remains unclear whether one can control the magnetic moment orientation efficiently because of the cancelled magnetic moment. Here, we report spin-orbit torque induced magnetization switching of ferrimagnetic Co1-xTbx films with perpendicular magnetic anisotropy. Current induced switching is demonstrated in all of the studied film compositions, including those near the magnetization compensation point. The spin-orbit torque induced effective field is further quantified in the domain wall moti…
Modern high-performance permanent magnets are made from alloys of rare earth and transition metal elements, and large magnetization is achieved in the alloys with high concentration of transition metals. We applied evolutionary search scheme based on first-principles calculations to the Y-Co-B system and predicted 37 cobalt-rich compounds with high probability of being stable. Focusing on remarkably cobalt-rich compounds, YCo$_{16}$ and YCo$_{20}$, we found that, although they are metastable phases, the phase stability is increased with increase of temperature due to the contribution of vibrat…
Magnetic bond-order potential for iron-cobalt alloys
本研究提出一种适用于铁钴合金的解析磁性键序势，经DFT数据拟合后可准确描述Fe-Co体系的电子结构、结构稳定性等特性，适用于大规模原子模拟。
Fabrication of Dense Ultrafine-Grained MoW, MoWNb, and MoWNbTa Alloys: Influence of Cobalt Doping on Sintering and Grain Growth
通过高能球磨和等离子体烧结制备超细晶MoW等合金，研究发现钴掺杂能显著提高烧结密度并抑制晶粒生长。
Cobalt-based alloys with γ/γ' microstructures have the potential to become the next generation of superalloys, but alloy compositions and processing steps must be optimized to improve coarsening, creep, and rafting behavior. While these behaviors are different than in nickel-based superalloys, alloy development can be accelerated by understanding the thermodynamic factors influencing microstructure evolution. In this work, we develop a phase field model informed by first-principles density functional theory and experimental data to predict the equilibrium shapes of Co-Al-W γ' precipitates. Thr…
The magnets are typically classified into Stoner and Heisenberg type, depending on the itinerant or localized nature of the constituent magnetic moments. In this work, we investigate theoretically the behaviour of the magnetic moments of iron and cobalt in their B2-ordered alloy. The results based on local spin density approximation (LSDA) for the density functional theory (DFT) suggest that the Co magnetic moment strongly depends on the directions of the surrounding magnetic moments, which usually indicates the Stoner-type mechanism of magnetism. This is consistent with the disordered local m…
The purpose of this study is to investigate the mechanisms involved in the wear of cobalt-based interfaces at high temperature. The studied contact is a cobalt-based alloy subjected to fretting against an alumina sample. At high temperature, a protective third body is spontaneously created at the interface and presents excellent tribological properties. The formation of the so-called ''glaze layer'' leads to an absence of wear. The investigation presents on complete description of the hightemperature tribolayer with microstructural, chemical and mechanical characterizations. The glaze layer re…
Computational insights into Cobalt-based novel half-Heusler alloy for sustainable energy applications
本文利用DFT和FLAPW方法系统研究半赫斯勒合金CoVAs的弹性、电子、磁性、热力学及光学性质，揭示其半金属铁磁性和高温应用潜力，并指出其在自旋电子学、光伏和光电领域的应用前景。
We propose a general rule for estimating the magnetic moments of Co$ 2$(cobalt)-based Heusler alloys, especially when doped with late transition metals. We come up with a descriptor that can characterise both pure Co$_2$YZ compounds and the doped ones with the chemical formula Co$_2$Y$_{1-x}$M$_x$Z (M is the dopant) using online data for magnetic moments of Heusler alloys with Co$_2$YZ structure and compressive sensing approach. The newly proposed descriptor not only depends on the number of valence electrons of the compound also it depends on the number of unoccupied d-electrons in the doping…
Magnetism, transport and atomic structure of amorphous binary YxCo1-x alloys
本文研究非晶 YxCo1-x 溅射薄膜的成分依赖磁性、原子堆积与输运行为，揭示 Co 磁矩在 x=0.50 消失，并通过 XMCD 和磁化转动模型阐明其软磁机制。
Structures of iron and cobalt bimetallic clusters for optimized chemical vapor deposition growth of single-walled carbon nanotubes
研究通过铁钴双金属簇优化化学气相沉积生长单壁碳纳米管，发现Fe0.75Co0.25合金在高温下促进大直径纳米管生长。
Formation of double ring patterns on Co2MnSi Heusler alloy thin film by anodic oxidation under scanning probe microscope
利用原子力显微镜（AFM）观察到Co2MnSi（CMS）薄膜在局部阳极氧化（LAO）过程中在电击穿电压下形成双环。利用磁力显微镜和能量色散谱研究了电晕效应和钴在环附近的偏析。双环的形成归因于LAO过程中烧蚀材料与感应磁场的相互作用。从CMS膜的未扰动区域的正向偏压输运特性的陡度表明非平衡自旋贡献。AFM针尖在磁性薄膜中的这种介观织构可以潜在地用于存储应用。
The existence of three fold rotational, mirror and time reversal symmetries often give rise to the triply degenerate nodal point (TP) in the band structure of a material. Based on point group symmetry analysis and first principle electronic structure, we predict, in this article, a series of quaternary Heusler alloys host an ideal platform for the occurrence of TP. We simulated, the projection of these TPs onto the (111) and (100) surfaces lead to form topological Fermi arcs, which may further be detected by scanning tunneling spectroscopy and angle resolved photoemission spectroscopy. These F…
Experiments identified Co3Sn2S2 as the first magnetic Weyl semimetal (MWSM). Using first-principles calculation with a global optimization approach, we explore the structural stabilities and topological electronic properties of cobalt (Co-based shandite and alloys, Co3MM-X2 (M/M-=Ge, Sn, Pb, X=S, Se, Te), and identify new stable structures with new Weyl phases. Using a tight-binding model, for the first time, we reveal that the physical origin of the nodal lines of a Co-based shandite structure is the interlayer coupling between Co atoms in different Kagome layers, while the number of Weyl poi…
Melting of alloys along the inter-phase boundaries in eutectic and peritectic systems
本文讨论了共晶和包晶系统中沿固-固界面熔化动力学的一个简单模型。该过程是由液相内的扩散控制的，并且三重连接点的存在对于速度选择问题至关重要。使用润滑近似在液相中的扩散场，我们得到缩放结果的稳态速度的移动模式取决于过热以上的平衡温度和系统的材料参数，包括依赖于在三重连接点的角度。
Dirac, triple-point and Weyl fermions represent three topological semimetal phases, characterized with a descending degree of band degeneracy, which have been realized separately in specific crystalline materials with different lattice symmetries. Here we demonstrate an alloy engineering approach to realize all three types of fermions in one single material system of MgTa$_{2-x}$Nb$_x$N$_3$. Based on symmetry analysis and first-principles calculations, we map out a phase diagram of topological order in the parameter space of alloy concentration and crystalline symmetry, where the intrinsic MgT…
Interstitial Solute Segregation at Triple Junctions: Implications for the Hydrogen Storage Properties of Nanomaterials
针对极细晶粒尺寸下三重点效应对间隙溶质偏析的影响，开发适用于Pd(H)多晶的间隙位点偏析计算框架，揭示尺寸依赖性机制，为间隙纳米晶合金界面工程提供基础并证明其可提升储氢密度。
Despite the growing interest in topological materials, the difficulty of experimentally synthesizing and integrating them with other materials has been one of the main barriers restricting access to their unique properties. Recent advances in synthesizing metastable phases of crystalline materials can help to overcome this barrier and offer new platforms to experimentally study and manipulate band topology. Because III-V semiconductors have a wide range of functional material applications (including optoelectronic devices, light-emitting diodes, and highly efficient solar cells), and because B…
Rapid Assessment of Stable Crystal Structures in Single Phase High Entropy Alloys Via Graph Neural Network Based Surrogate Modelling
本研究提出基于图神经网络ALIGNN-FF的单相高熵合金稳定结构快速预测方法，经132种合金测试并与传统方法对比，验证了多因素对精度的影响，还成功预测并实验验证了新型无钴3d高熵合金的结构。
Noble metal surfaces (Au, Ag and Cu etc.) have been extensively studied for the Shockley type surface states (SSs). Very recently, some of these Shockley SSs have been understood from the topological consideration, with the knowledge of global properties of electronic structure. In this letter, we show the existence of Dirac like excitations in the elemental noble metal Ru, Re and Os based on symmetry analysis and first principle calculations. The unique SSs driven Fermi arcs have been investigated in details for these metals. Our calculated SSs and Fermi arcs are consistent with the previous …
Layered Li(Ni,Mn,Co,)O$_2$ (NMC) presents an intriguing ternary alloy design space for optimization as a cathode material in Li-ion batteries. Recently, the high cost and resource limitations of Co have added a new design constraint and high Ni-containing NMC alloys have gained enormous attention despite possible performance trade-offs. It is not fully understood if this material space is a disordered solid solution at room temperature and any arbitrary combination can be used or if there exist distinct transition metal orderings to which meta-stable solid solutions will decay during cycling a…
Microstructure evolution and heterogeneous nucleation in ternary Al-Cu-Ni alloys
采用多相场模型对三元Al-Cu-Ni合金的凝固过程进行了模拟，结果表明，通过耦合各相的真实热力学参数和演化方程，可以得到真实的微观组织。对模型函数的各个界面的稳定性要求保证了在$n$维相场空间中不存在“鬼”相。特别构造的热噪声项干扰了稳定性，并可根据能量和浓度条件产生产物相的异相成核。特别感兴趣的是，在三相点中，第四相的成核发生而没有额外的噪声。另一个观察结果是在各种合金中的共晶状或包晶状结构的生长。
High-Temperature Deformation Behavior of Co-Free Non-Equiatomic CrMnFeNi Alloy
研究无钴非等原子CrMnFeNi合金高温变形行为，通过拉伸试验、分子动力学模拟、电子背散射衍射等方法，揭示其热激活变形机制、微观结构演变及孪晶等情况，发现无钴使其高温强度增强。
Non-collinear magnetic ordering in compressed FePd$_3$ ordered alloy: a first principles study
采用基于密度泛函理论的从头计算方法研究了有序FePd $_3$合金的磁相图随外压的变化。考虑到几种磁组态，我们得出结论，在压力下的系统有一个非共线自旋排列的趋势。海森堡交换参数$J_{ij}$的分析表明，铁-铁磁耦合对Pd原子的极化有很强的依赖性。考虑到后者的影响，我们建立了一个扩展的海森堡模型与高阶（双二次）条款。最小化这个哈密顿量的能量，充分参数化使用从头计算的结果，我们发现了一个候选人的压缩FePd $_3$，这可以被看作是两个相互渗透的“三重Q”相的基态。
We present results on the identification of phase transitions in ferrimagnetic GdFeCo alloys using machine learning. The approach for finding phase transitions in the system is based on the `learning by confusion' scheme, which allows one to characterize phase transitions using a universal $W$-shape. By applying the `learning by confusion' scheme, we obtain 2D $W$-a shaped surface that characterizes a triple phase transition point of the GdFeCo alloy. We demonstrate that our results are in the perfect agreement with the procedure of the numerical minimization of the thermodynamical potential, …
Ab initio High-Pressure Phase Diagrams of Al-Mg Alloys in the Low Solute Concentration Limit
该研究采用从头算方法计算了Al-Mg合金低压溶质极限下的高压相图，揭示了富Mg侧Al的固液分配随压力反转的新规律，对行星内部模型有重要意义。
New phase space of hardness materials and synergic enhancement of hardness and toughness in superconducting Ti2Co and Ti4Co2X (X = B, C, N, O)
研究发现立方合金Ti2Co硬度远超理论预测且韧性极低，通过间隙掺氧可同时提升硬度和韧性，源于金属键与共价键共存，扩展了合金材料相空间。
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