在本报告中，我们回顾了磁性材料原子间交换相互作用的显式计算方法。这涉及通常被称为 Heisenberg 交换、Dzyaloshinskii-Moriya 相互作用和各向异性对称交换的交换机制。我们详细给出了微观电子结构理论（如密度泛函理论或动力学平均场理论）与原子间交换之间的联系。文章强调了从考虑显著较少原子（1-50个）的电子结构计算中，提取涉及数千个原子的有效自旋哈密顿量信息的不同方面。我们展示了一大类材料的交换相互作用实例，包括 3d 周期的重元素、过渡金属间的合金、Heusler 化合物、多层系统以及基底上的覆盖层和吸附原子、过渡金属氧化物、4f 元素、二维磁性材料和分子磁体。在可能的情况下，我们与实验数据进行了比较，这种比较自然地集中在磁振子色散上。我们在少数情况下回顾了相对论的影响，以及动态关联的重要性。本文还描述了处理非平衡条件理论的发展。综述最后简要描述了将原子间交换显式计算背后的理论扩展到非磁性情况的进展，例如描述化学（电荷）序和超导性。
英文摘要：
In this report we review the method of explicit calculations of interatomic exchange interactions of magnetic materials. This involves exchange mechanisms normally referred to as Heisenberg exchange, Dzyaloshinskii-Moriya interaction and anisotropic symmetric exchange. The connection between microscopic theories of the electronic structure, such as density functional theory or dynamical mean field theory, and interatomic exchange, is given in detail. The different aspects of extracting information for an effective spin Hamiltonian that involves thousands of atoms, from electronic structure calculations considering significantly fewer atoms (1-50) is highlighted. Examples of exchange interactions of a large group of materials is presented, which involves heavy elements of the 3d period, alloys between transition metals, Heusler compounds, multilayer systems as well as overlayers and adatoms on a substrate, transition metal oxides, 4f elements, magnetic materials in two dimensions and molecular magnets. Where possible, a comparison to experimental data is made, that naturally becomes focused on the magnon dispersion. The influence of relativity is reviewed for a few cases, as is the importance of dynamical correlations. Development to theories that handle out of equilibrium conditions is also described here. The review ends with a short description of extensions of the theories behind explicit calculations of interatomic exchange, to non-magnetic situations, e.g. that describe chemical (charge) order and superconductivity.
A vector order parameter phase field model derived from a grand potential functional is presented as a new approach for modeling polycrystalline solidification of alloys. In this approach, the grand potential density is designed to contain a discrete set of finite wells, a feature that naturally allows for the growth and controlled interaction of multiple grains using a single vector field. We verify that dendritic solidification in binary alloys follows the well-established quantitative behavior in the thin interface limit. In addition, it is shown that grain boundary energy and solute back-d…
A comparative study of the magnetic and magnetotransport properties between a metallic (x=0.6) and a semiconducting (x=0.2) member of the solid solution LaNixCo1-xO3
Realizing solution processed quantum dot (QD) lasers is one of the holy-grails of nanoscience. The reason that QD lasers are not yet commercialized is that the lasing threshold is too high: one needs > 1 exciton per QD, which is hard to achieve due to fast non-radiative Auger recombination. The optical gain threshold can be reduced by electronic doping of the QDs, which lowers the absorption near the band-edge, such that the stimulated emission (SE) can easily outcompete absorption. Here, we show that by electrochemically doping films of CdSe/CdS/ZnS QDs we achieve quantitative control over th…
Evolution of magnetic properties in the normal spinel solid solution Mg(1-x)Cu(x)Cr2O4
我们研究了普通尖晶石氧化物Mg（1-x）Cu（x）Cr2 O 4的磁性的演变，使用磁化强度和热容测量。固溶体系列的端元化合物由于其非常有趣的磁性行为而被详细研究。MgCr_2O_4是一个高阻挫体系，在反铁磁有序温度下发生一级结构转变。CuCr_2O_4在室温下是四面体结构，是Jahn-Teller活性四面体Cu^2+的结果，在135 K时发生磁转变。在组成系列Mg（1-x）Cu（x）Cr2 O 4的四面体A位上，磁性阳离子取代抗磁性Mg^2+会显著影响磁性行为。在0 < x < 0.3的组成范围内，化合物是反铁磁性的。在12.5K时观察到的MgCr_2 O_4的热容量中对应于磁驱动的一级结构转变的尖锐峰被抑制，即使对于小的x表明玻璃态无序。在x范围0.43 < x < 1的样品中，未补偿的磁性-具有开放的磁化回路-发展。在0.43 < x < 0.47的中间组成范围内出现多个磁有序温度和大的矫顽场。Neel温度随着整个系列中x的增加而增加，而Curie-Weiss Theta的值减小。给出了该固溶体系列的磁性温度-成分相图。
Samples consisting of one ferromagnetic and one diamagnetic component which are immiscible at the thermodynamic equilibrium (Co-Cu, Fe-Cu, Fe-Ag) are processed by high-pressure torsion at various compositions. The received microstructures are investigated by electron microscopy and synchrotron X-ray diffraction, showing a microstructural saturation. Results gained from microstructural investigations are correlated to magnetometry data. The Co-Cu samples show mainly ferromagnetic behavior and a decrease in coercivity with increasing Co-content. The saturation microstructure of Fe-Cu samples is …
Structural and Magnetic Phase Transitions in MnTe-MnSe solid solutions
用中子衍射方法研究了富硒区MnSe和MnTe固溶体随温度的变化。有趣的是，当Te掺杂在MnSe中时，向NiAs相的结构转变减小，无论是在化合物的分数方面还是在转变温度方面。在MnTe $_{0.3}$ Se $_{0.7}$中，NaCl向NiAs的相变发生在40 K左右，虽然在室温下存在于MnTe $_{0.5}$ Se $_{0.5}$中，但其体积分数仅占样品总体积的10%左右.立方相的磁有序温度随Te含量的增加而降低，而六方相的顺序在相同的温度下，在MnSe。在磁有序以及结构转变温度的晶格参数的热演化的异常表明在这些化合物的磁结构耦合的存在。
This paper presents an efficient and quantitative phase-field model for elastically heterogeneous alloys that ensures the two mechanical compatibilities$\unicode{x2014}$static and kinematic, in conjunction with chemical equilibrium within the interfacial region. Our model contrasts with existing phase-field models that either violate static compatibility or interfacial chemical equilibrium or are computationally costly. For computational efficiency, the partial rank-one homogenization (PRH) scheme is employed to enforce both static and kinematic compatibilities at the interface. Moreover, inte…
Magnetic Behaviour of the $Bi_{2-y} Sr_y Ir_2 O_7$ Pyrochlore Solid Solution
研究了Bi $_{2-y}$ Sr $_{y}$ Ir $_{2}$ O $_{7}$体系在2 ~ 300 K温度范围内的磁化率随温度的变化关系。根据这些测量结果，固溶体$(0\leq y\leq 0.9)$没有显示出任何磁转变;然而，从居里-外斯定律发生了明显的偏离，并且该系统的磁行为可以归因于短程磁序，这也存在于几个几何阻挫系统中。泡利磁化率随着Sr含量的增加而降低，这可以与样品中向Ir $^{5+}$的偏移相关联; Ir的有效磁矩也降低。估计的威尔逊比表明存在强的电子-电子相关。
Three-dimensional topological solitons attract a great deal of interest in fields ranging from particle physics to cosmology but remain experimentally elusive in solid-state magnets. Here we numerically predict magnetic heliknotons, an embodiment of such nonzero-Hopf-index solitons localized in all spatial dimensions while embedded in a helical or conical background of chiral magnets. We describe conditions under which heliknotons emerge as metastable or ground-state localized nonsingular structures with fascinating knots of magnetization field in widely studied materials. We demonstrate magne…
The spin Seebeck effect (SSE) refers to the generation of a spin current as a result of a temperature gradient in a magnetic material, which can be detected electrically via the inverse spin Hall effect in a metallic contact. Since the discovery of SSE in 2008, intensive studies on SSE have been conducted to elucidate its origin. SSEs appear in a wide range of magnetic materials including ferro-, ferri-, and antiferro-magnets and also paramagnets with classical or quantum spin fluctuation. SSE voltage reflects fundamental properties of a magnet, such as elementary excitation, static magnetic o…
The relativistic Dirac equation covers the fundamentals of electronic phenomena in solids and as such it effectively describes the electronic states of the topological insulators like Bi$_2$Se$_3$ and Bi$_2$Te$_3$. Topological insulators feature gapless surface states and, moreover, magnetic doping and resultant ferromagnetic ordering break time-reversal symmetry to realize quantum anomalous Hall and Chern insulators. Here we focus on the bulk and investigate the mutual coupling of electronic and magnetic properties of Dirac electrons. Without carrier doping, spiral magnetic orders cause a fer…
Mott-insulator to commensurate-solid transition in a 4He layer on α-graphyne: Pseudo-spin symmetry breaking under a particle-induced pseudo-magnetic field
One of the major challenges in modern robotics is controlling micromanipulation by active and adaptive materials. In the respiratory system, such actuation enables pathogen clearance by means of motile cilia. While various types of artificial cilia have been engineered recently, they often involve complex manufacturing protocols and focus on transporting liquids only. Here, we create soft magnetic carpets via an easy self-assembly route based on the Rosensweig instability. These carpets can transport liquids but also solid objects that are larger and heavier than the artificial cilia, using a …
