Because of large spatial separation of the Mn atoms in Heusler alloys the Mn 3d states belonging to different atoms do not overlap considerably. Therefore an indirect exchange interaction between Mn atoms should play a crucial role in the ferromagnetism of the systems. To study the nature of the ferromagnetism of various Mn-based semi- and full-Heusler alloys we perform a systematic first-principles calculation of the exchange interactions in these materials. The calculation of the exchange parameters is based on the frozen-magnon approach. The calculations show that the magnetism of the Mn-based Heusler alloys depends strongly on the number of conduction electrons, their spin polarization and the position of the unoccupied Mn 3d states with respect to the Fermi level. Various magnetic phases are obtained depending on the combination of these characteristics. The Anderson's s-d model is used to perform a qualitative analysis of the obtained results. The conditions leading to diverse magnetic behavior are identified. If the spin polarization of the conduction electrons at the Fermi energy is large and the unoccupied Mn 3d states lie well above the Fermi level, an RKKY-type ferromagnetic interaction is dominating. On the other hand, the contribution of the antiferromagnetic superexchange becomes important if unoccupied Mn 3d states lie close to the Fermi energy. The resulting magnetic behavior depends on the competition of these two exchange mechanisms. The calculational results are in good correlation with the conclusions made on the basis of the Anderson s-d model which provides useful framework for the analysis of the results of first-principles calculations and helps to formulate the conditions for high Curie temperature.
Theory of Huge Thermoelectric Effect Based on Magnon Drag Mechanism: Application to Thin-Film Heusler Alloy
为了理解在薄膜Heusler合金Fe $_2$ V $_{0.8}$ W $_{0.2}$ Al中观察到的出乎意料的高热电性能，我们研究了由钨基杂质带产生的磁振子拖曳效应，作为这种增强的可能来源，类似于在FeSb $_2$中观察到的声子拖曳。假设薄膜Heusler合金具有与杂质带结合的导带，由钨替代产生，我们基于自洽t矩阵近似推导了电导率$L_{11}$，基于线性响应理论推导了磁振子拖曳引起的热电电导率$L_{12}$，并估算了电阻率、Seebeck系数和功率因数随温度的变化.最后，我们将理论结果与薄膜Heusler合金的实验结果进行了比较，结果表明，异常热电性能的起源很可能是由于与钨基杂质带相关的磁振子阻力。
Simulations with machine learning potentials identify the ion conduction mechanism mediating non-Arrhenius behavior in LGPS
Li $_{10}$ Ge（PS $_6$）$_2$（LGPS）是一种高度浓缩的固体电解质，其中相邻阳离子之间的库仑排斥被假设为协同离子跳跃的根本原因，协同离子跳跃是诸如Li $_7$ La $_3$ Zr $_2$ O $_{12}$（LLZO）和Li $_{1.3}$ Al $_{0.3}$ Ti $_{1.7}$（PO $_4$）$_{1.7}$（LATP）的超离子导体中常见的机制。虽然使用分子动力学（MD）的第一性原理模拟提供了对Li $^+$传输机制的深入了解，但从历史上看，在模拟和实验中研究的温度范围存在差距。在这里，我们使用了在密度泛函理论（DFT）模拟上训练的神经网络（NN）势，以DFT般的精度运行长达40纳秒的MD模拟，以表征包括先前模拟和实验研究在内的温度范围内的离子传导机制。我们已经证实了锂$^+$亚晶格相变在LGPS约400 K，低于该\textit{ab}平面扩散率$D^*_{ab}$急剧减少。伴随着400 K附近的亚晶格相变，有较少的阳离子-阳离子（交叉）相关性，其特征在于Haven比接近1，并且在较低的温度下，系统中的振动更谐波。直觉上，在高温下，振动模式的收集可能足以驱动协同离子跳跃。然而，在接近室温时，可用的振动模式可能不足以克服静电排斥，从而导致相关性较低的离子运动和相对较慢的离子传导。这种亚晶格相变的现象，在其以下协调跳跃起不太重要的作用，可以…
Pt-induced semimetallic transport and enhanced thermoelectric response in the half-Heusler alloy YNi_{0.5}Pt_{0.5}Bi
Indian Institute of Technology Delhi（印度德里理工学院）；Harbin Institute of Technology（哈尔滨工业大学）；Chalmers University of Technology（查尔姆斯理工大学）；Damanhour University（达曼胡尔大学）；Max-Planck-Institut für Chemische Physik fester Stoffe（马克斯·普朗克固体化学物理研究所）；Tohoku University（东北大学）
Superconductivity mediated by the antiferromagnetic spin-wave in chalcogenide iron-base superconductors
K $_{0.8+x}$ Fe $_{1.6+y}$ Se $_2$等铁基硒化物超导体的基态都是掺杂反铁磁半导体。在这些材料中，存在定义明确的铁局域矩，其能量与传导电子的能量通过大的带隙分开。我们建议，该系统的低能物理是由一个模型的相互作用的电子与现场铁磁交换相互作用和站点间的超交换相互作用的哈密顿量。我们在线性自旋波近似下导出了电子的有效配对势，并证明了这些材料中的超导性可以通过介导相干自旋波激发来驱动。我们的工作为中子散射和其他实验观察到的超导和反铁磁长程序共存提供了一个自然的解释。
