The dynamics of magnetic moments in iron-chromium alloys with different levels of Cr clustering show unusual features resulting from the fact that even in a perfect body-centred cubic structure, magnetic moments experience geometric magnetic frustration resembling that of a spin glass. Due to the long range exchange coupling and configuration randomness, magnetic moments of Cr solutes remain non-collinear at all temperatures. To characterise magnetic properties of Fe-Cr alloys, we explore the temperature dependence of magnetisation, susceptibility, Curie temperature and spin-spin correlations with spatial resolution. The static and dynamic magnetic properties are correlated with the microstructure of Fe-Cr, where magnetisation and susceptibility are determined by the size of Cr precipitates at nominal Cr concentrations. The Curie temperature is always maximised when the solute concentration of Cr in the $α$ phase is close to 5 to 6 at.\%, and the susceptibility of Fe atoms is always enhanced at the boundary between a precipitate and solid solution. Interaction between Cr and Fe stimulates magnetic disorder, lowering the effective Curie temperature. Dynamic simulation of evolution of magnetic correlations shows that the spin-spin relaxation time in Fe-Cr alloys is in the 20 to 40 ps range.
We report a study on the electronic and magnetic properties of a novel Rb$_{x}$Sr$_{1-x}$C alloy. We find that the variation of the lattice parameter as function of Rb composition exhibits a deviation from the Vegard's law of about 0.4 Å. The total energy results predict a ferromagnetic ordering for Sr-rich alloy, and antiferromagnetic ordering for RbC-rich alloy with a total magnetic moment ranging from 2 to 3$μ_\text{B}$ per cation. As for the parent compounds, RbC and SrC, the origin of magnetism arises from the polarization of the carbon $p$-orbitals. From the spin-polarized calculations, …
Electronic structure and magnetism in disordered bcc Fe alloys
本文采用增强空间递归方法结合紧束缚线性松饼锡轨道（TB-LMTO）方法研究了bcc结构Co $_{x}$ Fe $_{1-x}$，Cr $_{x}$ Fe $_{1-x}$和Mn $_{x}$ Fe $_{1-x}$的电子结构和磁性.本文系统地研究了磁矩和居里温度等磁性，并从电荷转移、交换分裂和杂化等效应出发，对3-{ \it d}过渡金属系列的磁矩和居里温度的变化规律进行了讨论。
Magnetism: the Driving Force of Order in CoPt. A First-Principles Study
CoPt或FePt等原子合金按照有利于其强磁各向异性的四元L10结构有序化。相反，磁性可以影响化学有序。本文用{ \it ab initio}方法计算了Co-Pt合金在顺磁和铁磁状态下的L10和L12结构的稳定性。他们表明，磁性强烈地加强了这个系统中的有序趋势。一个简单的紧约束分析允许我们用一些相关参数来解释这种行为。
Spintronics is the fast growing field that will play a key role in optimizing power consumption, memory, and processing capabilities of nanoelectronic devices. Heusler alloys are potential candidates for application in spintronics due to their room temperature (RT) half-metallicity, high Curie temperature, low lattice mismatch with most substrates, and strong control on electronic density of states at Fermi level. In this work, we investigate the effect of {substitutional doping and disorder} on the half-metallicity, phase stability, and magnetism of Heusler alloys using density functional the…
A recent experimental study (Phys. Rev. Appl. 9, 024023, 2018) on paramagnetic CeCo$_3$ finds that Magnesium alloying induces a ferromagnetic transition with intrinsic properties large enough for permanent magnet applications. Here we explain these surprising results \textit{via} a first principles study of the electronic structure and magnetism of Magnesium-alloyed CeCo$_3$. We find the origin of this Magnesium-induced ferromagnetic transition to be Stoner physics - the substantial increase in the Fermi-level density-of-states $N(E_F)$ with Mg alloying. Our calculations suggest that both Ce a…
In 1965 Duwez \textit{et al.} reported having generated an amorphous, stable phase of palladium-silicon in the region 15 to 23 atomic percent (at. \%) silicon. These pioneering efforts have led to the development of solid materials that are now known as Bulk Metallic Glasses (BMG). In 2019 we discovered, computationally, that bulk amorphous Pd becomes magnetic, and so does porous/amorphous Pd. Puzzled by our results we undertook the study of several solid binary systems in the Pd-rich zone; in particular, the study of the glassy metallic alloy $a$-Pd$_{100-c}$Si$_{c}$, for $0 \leq c \leq 22$, …
Designing magnetism in Fe-based Heusler alloys: a machine learning approach
结合材料信息学和高通量电子结构计算提供了快速表征复杂磁性材料的可能性。在这里，我们证明了在从头计算水平上计算的电子性质数据集可以有效地用于识别和理解磁性材料的物理趋势，从而为加速材料发现开辟了新的途径。以数据为中心的方法之后，我们利用在密度泛函理论水平计算的Heusler合金的数据库来识别在$X_2$ Fe $Z$ Heusler原型中邻近Fe的理想离子。Fe与最近邻的$X$离子的杂化被发现会引起原位Fe电荷的重新分布和其磁矩的净增加，其磁矩与$X$的价态成正比。因此，后过渡金属是生产高磁矩铁基Heusler磁体的理想Fe邻居。同时，热力学稳定性分析发现，限制$Z$的主族元素。机器学习回归器，训练预测磁矩和赫斯勒合金的体积，用于确定属于所提出的原型的所有材料的磁化。我们发现Co $_2$ Fe $Z$合金，特别是Co $_2$ FeSi，使磁化强度最大化，其达到高达1.2T的值。这是在良好的协议与从头算和实验数据。此外，我们确定Cu $_2$ Fe $Z$系列是具有成本效益的材料类别，提供约0.65 T的磁化强度。
Interstitial Fe-Cr alloys: Tuning of magnetism by nanoscale structural control and by implantation of nonmagnetic atoms
使用密度泛函理论，我们进行了一个完整的原子弛豫的散装铁氧体与12.5%的浓度的单原子间隙Cr周期性地位于bcc Fe $_α$细胞的边缘。我们表明，在这种人工设计的合金结构弛豫导致显着的原子位移，并在形成新的高度稳定的配置与平行链的八面体排列的铁的结果。这种类型的合金的低对称金属状态下的增强的磁极化可以通过额外包含诸如氮的非金属杂质来外部控制。我们讨论了生成的间隙合金在自旋电子器件中的可能应用，并建议将其作为新型耐用不锈钢的基础。
Compositionally complex materials (CCMs) present a potential paradigm shift in the design of magnetic materials. These alloys exhibit long-range structural order coupled with limited or no chemical order. As a result, extreme local environments exist with a large opposing magnetic energy term, which can manifest large changes in the magnetic behavior. In the current work, the magnetic properties of (Cr, Mn, Fe, Ni) alloys are presented. These materials were prepared by room-temperature combinatorial sputtering, resulting in a range of compositions with a single BCC structural phase and no chem…
Room temperature solute clustering in aluminium alloys, or natural ageing, despite its industrial relevance, is still subject to debate, mostly due to its experimentally challenging nature. To better understand the complex multi-constituents' interactions at play, we have studied ternary and quaternary subsystems based on the Al-Cu alloys, namely Al-Cu-Mg, Al-Cu-Li and Al-Cu-Li-Mg. We used a recently introduced correlative technique using small-angle neutrons and X-ray scattering (SANS and SAXS) to extract the chemically resolved kinetics of room temperature clustering in these alloys, which w…
Magnetism of mixed quaternary Heusler alloys: (Ni,T)$_{2}$MnSn (T=Cu,Pd) as a case study
采用{ \it ab initio}计算方法研究了Cu和Pd掺杂的无规四元Heusler Ni $_{2}$ MnSn合金的电子性质、交换作用、有限温度磁性和输运性质.虽然磁矩仅弱地依赖于合金成分，但居里温度相对于Cu掺杂表现出强烈的非线性行为，而在Pd掺杂的情况下几乎是线性的浓度依赖性。目前的无参数理论同意定性，也相当好地定量与现有的实验结果。交换互动的分析提供了一个更深入的理解这个问题。掺杂剂原子仅微弱地扰动接近费米能的电子结构，并且剩余电阻率因此服从简单的Nordheim规则。对温度依赖性电阻率的主要贡献是由于自旋无序引起的电子涨落，根据我们的计算，这可以通过无序局域矩模型成功地描述。基于此模型的计算结果与自旋无序感生电阻率的测量值吻合得相当好。
A nexus between 3D atomistic data hybrids derived from atom probe microscopy and computational materials science: a new analysis of solute clustering in Al-alloys
In general, conventional superconductivity and magnetism are competing phenomena. In some alloys this competition is a function of the concentration of the elements. Here we show that in the palladium alloys Pd$_{1-c}$(H/D/T)$_{c}$ (Pd-ides) the increase in the concentration $c$ of the ides: hydrogen, deuterium, tritium (H/D/T), lowers the predicted magnetism of amorphous palladium ($a$-Pd) gradually, allowing superconductivity to appear for $ c \approx 40\%$. This magnetism explains why superconductivity does not manifest for smaller values of $c$ ($c \leq 40\%$) in these Pd alloys. Also, the…
We have studied the properties of relatively thick (about 120 nm) magnetic composite films grown by pulsed laser deposition method using (GaSb)$_{0.59}$(MnSb)$_{0.41}$ eutectic compound as a target for sputtering. For the studied films we have observed ferromagnetism and anomalous Hall effect above the room temperature, it manifests the presence of spin-polarized carriers. Electron microscopy, atomic and magnetic force microscopy results suggests that films under study have homogenous columnar structure in the bulk while MnSb inclusions accumulate near it's surface. This is in good agreement w…
Deploying an analytical atomistic model of the bulk band structure of the IV-VI semiconductors we connect the spin structure of the topological surface state to the crystal field and spin orbit coupling parameters of the bulk material. While the Dirac-Weyl (or equivalently, Rashba) type topological surface state is often assumed universal, we show that the physics of the surface state is strikingly non-universal. To see this explicitly we calculate the RKKY interaction, which may be viewed as a probe of this surface state spin structure, finding its \emph{qualitative form} depends on the value…
Enhancing the magnetism and giant anomalous Hall effect in thin Fe-Al films via B2 nanophase growth
Lobachevsky State University of Nizhny Novgorod（下诺夫哥罗德洛巴切夫斯基国立大学）；Institute for Physics of Microstructures, Russian Academy of Sciences（俄罗斯科学院微观结构物理研究所）
We present the results of ab initio modeling of structure of dilute Ti-Fe, a typical representative of quenched Ti-based transition-metal alloys. We have demonstrated that beyond the solubility limit this alloy cannot be described in common terms of substitutional and interstitial alloys. Instead, very stable local clusters are formed in both low-temperature hcp and high-temperature bcc phases of alloys, with almost identical local structures. This gives an example of geometrically frustrated state and explains unusual concentration behavior of Mössbauer spectra discovered long ago for this sy…
