Applying the local density and dynamical mean field approximations to paramagnetic γ-iron we revisit the problem of theoretical description of magnetic properties in a wide temperature range. We show that contrary to α-iron, the frequency dependence of the electronic self-energy has a quasiparticle form for both, t_{2g} and e_g states. In the temperature range T=1200-1500 K, where γ-iron exist in nature, this substance can be nevertheless characterized by temperature-dependent effective local moments, which yield relatively narrow peaks in the real part of the local magnetic susceptibility. At the same time, at low temperatures γ-iron (which is realized in precipitates) is better described in terms of itinerant picture. In particular, the nesting features of the Fermi surfaces yield maximum of the static magnetic susceptibility at the incommensurate wave vector q_{max} belonging the direction q_X-q_W (q_X=(2π/a)(1,0,0),q_W=(2π/a)(1,1/2,0), a is a lattice parameter) in agreement with the experimental data. This state is found however to compete closely with the states characterized by magnetic wave vectors along the directions q_X-q_L-q_K, where q_L=(2π/a)(1/2,1/2,1/2), q_K=(2π/a)(3/4,3/4,0). From the analysis of the uniform magnetic susceptibility we find that contrary to α-iron, the Curie-Weiss law is not fulfilled in a broad temperature range, although the inverse susceptibility is nearly linear in the moderate-temperature region (1200-1500 K). The non-linearity of the inverse uniform magnetic susceptibility in a broader temperature range is due to the density of states peak located close to the Fermi level. The effective exchange integrals in the paramagnetic phase are estimated on the base of momentum dependent susceptibility.
New radical cation salt $κ$-(BETS)$_2$Co$_{0.13}$Mn$_{0.87}$[N(CN)$_2$]$_3$ with two magnetic metals: synthesis, structure, conductivity and magnetic peculiarities
合成了一种新的金属自由基阳离子盐$κ$ -（BETS）$_2$ Co $_{0.13}$ Mn $_{0.87}$ [N（CN）$_2$ ] $_3$，其中BETS为双（亚乙基二硫代）四硒富瓦烯，C $_{10}$ S $_4$ Se $_4$ H $_8$。在该盐中，一部分Mn $^{2+}$离子被Co $^{2+}$取代，Co $^{2+}$充当具有不同有效磁矩的磁性掺杂剂。研究了该盐的晶体结构、能带结构、导电和磁性。在30 K以下，材料经历金属-绝缘体转变，通过施加约0.5kbar的压力来抑制，导致超导基态。虽然结构和导电性质与母体盐$κ$ -（BETS）$_2$ Mn[N（CN）$_2$ ] $_3$的结构和导电性质非常相似，但发现与阴离子层中的局部磁矩相关的磁性惊人地不同。
The ground ytterbium doublet in h-YbMnO3 and the related low-temperature peculiarities of the compound
Institute of Spectroscopy, Russian Academy of Sciences（俄罗斯科学院光谱研究所）；Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences（中国科学院合肥物质科学研究院固体物理研究所材料物理重点实验室）
Orbital loop currents in iron-based superconductors
我们发现，通常观察到的铁基超导体的相图中的反铁磁状态必然触发回路电流的特征在于不同的Fe $ 3d $轨道之间的电荷转移。这种效应是植根于这些材料的滑移面对称性和存在的原子自旋轨道耦合，耦合状态的$X$和$Y$点的1-Fe布里渊区。在磁矩平行于磁有序矢量方向排列的特定情况下，这是铁基超导体中最常见的磁矩配置，这些环电流涉及$d_{xy}$轨道和$d_{yz}$轨道（如果磁矩指向$y$轴）或$d_{xz}$轨道（如果磁矩指向$x$轴）。我们发现，轨道环电流的两个主要表现形式是出现的磁矩在磷属元素化物/硫属元素网站和轨道选择性带分裂的磁有序状态，这两个都可以通过实验检测。我们的研究结果突出了铁基超导体中轨道和自旋自由度之间的独特交织，并揭示了可能影响这些材料正常状态和超导特性的不寻常相关相的出现。
Orbital selective local moment formation in iron: first principle route to an effective model
我们重新讨论了α-铁的理论描述问题。通过在顺磁相中进行LDA+DMFT计算，我们发现库仑相互作用，特别是Hund交换，产生了e_g电子带中的局部矩，这可以从自旋-自旋关联函数的虚时间依赖性来追踪。这种行为伴随着e_g电子的非费米液体行为，并建议在铁的有效模型中使用局部矩变量。通过研究Hund交换I= 0.9eV时Curie-Weiss定律的轨道选择性贡献，我们得到了e_g电子的有效局域磁矩2 p =1.04 μ_B。提出了描述铁在磁相变附近磁性的有效玻色子模型。
Properties of iron oxides at the extreme conditions are of essential importance in condensed matter physics and Geophysics. The recent discovery of a new type of iron oxide, Fe4O5, at high pressure and high temperature of Earth's deep interior attracts great interests. In this paper, we report the electronic structure and the magnetic properties of Fe4O5 predicted by the density functional theory plus dynamic mean field theory (DFT+DMFT) approach. We find that Fe4O5 stays metallic from ambient pressure to high pressure. The magnetic moments of iron atoms at the three different crystallographic…
We study the electronic and magnetic properties of L1$_0$ phase of FeNi, a perspective rare-earth-free permanent magnet, by using a combination of density functional and dynamical mean-field theory. Although L1$_0$ FeNi has a slightly tetragonally distorted fcc lattice, we find that magnetic properties of its constituent Fe atoms resemble those in pure bcc Fe. In particular, our results indicate the presence of well-localized magnetic moments on Fe sites, which are formed due to Hund's exchange. At the same time, magnetism of Ni sites is much more itinerant. Similarly to pure bcc Fe, the self-…
In the iron-pnictide material CeFeAsO not only the Fe moments, but also the local 4f moments of the Ce order antiferromagnetically at low temperatures. We elucidate on the peculiar role of the Ce on the emergence of superconductivity. While application of pressure suppresses the iron SDW ordering temperature monotonously up to 4 GPa, the Ce-4f magnetism is stabilized, until both types of magnetic orders disappear abruptly and a narrow SC dome develops. With further increasing pressure characteristics of a Kondo-lattice system become more and more apparent in the electrical resistivity. This su…
Spin current -- a flow of the spin degree of freedom in matter -- has vital importance in spintronics. Propagation of the spin current ranges over a whole momentum space; however, generated spin currents are mainly detected in the long-wavelength limit. To facilitate practical uses of spintronics and magnonics, microscopic understanding of the spin current is necessary. We here address yttrium iron garnet, which is a well-employed ferrimagnet for spintronics, and review {\it in re} the momentum- and energy-resolved characteristics of its magnetism. Using {\it unpolarized} neutrons, we refined …
