The ability to tune the iron chalcogenides BaFe2Q3 from Mott insulators, to metals and then superconductors with applied pressure has renewed interest in low-dimensional iron chalcogenides and oxychalcogenides. We report here a combined experimental and theoretical study on the iron oxychalcogenides BaFe2Q2O (Q=S, Se) and show that their magnetic behaviour results from nearest-neighbour magnetic exchange interactions via oxide and selenide anions of similar strength, with properties consistent with more localised electronic structures than those of BaFe2Q3 systems.
An insulating ferromagnetic (FM) phase exists in the quasi-one-dimensional iron chalcogenide Ce$_2$O$_2$FeSe$_2$ but its origin is unknown. To understand the FM mechanism, here a systematic investigation of this material is provided, analyzing the competition between ferromagnetic and antiferromagnetic tendencies and the interplay of hoppings, Coulomb interactions, Hund's coupling, and crystal-field splittings. Our intuitive analysis based on second-order perturbation theory shows that large entanglements between doubly-occupied and half-filled orbitals play a key role in stabilizing the FM or…
We present the results of structural and magnetic phase comparisons of the iron oxychalcogenides La$_{2}$O$_{2}$Fe$_{2}$O$M$$_{2}$ ($M$ = S, Se). Elastic neutron scattering reveals that $M$ = S and Se have similar nuclear structures at room and low temperatures. We find that both materials obtain antiferromagnetic ordering at a Neel temperature $T_{N}$ 90.1 $\pm$ 0.16 K and 107.2 $\pm$ 0.06 K for $M$= Se and S, respectively. The magnetic arrangements of $M$ = S, Se are obtained through Rietveld refinement. We find the order parameter exponent $β$ to be 0.129 $\pm$ 0.006 for $M$ = Se and 0.133 …
Mott-Kondo Insulator Behavior in the Iron Oxychalcogenides
我们对铁氧硫族化合物（FeO $\emph{Ch}$）系列La $_{2}$ O $_{2}$ Fe $_{2}$ O \emph{M} $_{2}$（\emph{M} =S，Se）进行了实验和理论研究，这是铁基材料中最新的具有非常规高温$_{c}$超导性（HTSC）的材料。结合X射线吸收（XAS）和共振非弹性X射线散射（RIXS）谱中的非相干Hubbard特征以及电阻率数据，揭示了母体FeO $\emph{Ch}$是相关驱动的绝缘体。为了揭示这些发现的微观基础，我们进行局域密度近似加动力学平均场论（LDA+DMFT）计算，解开莫特近藤绝缘状态。基于理论和一系列数据之间的良好一致性，我们提出，FeO $\emph{Ch}$可能构成一个新的，理想的试验场，探索HTSC所产生的一种奇怪的金属接近一种新的选择性莫特量子临界。
Nematic fluctuations occur in a wide range of physical systems from liquid crystals to biological molecules to solids such as exotic magnets, cuprates and iron-based high-$T_c$ superconductors. Nematic fluctuations are thought to be closely linked to the formation of Cooper-pairs in iron-based superconductors. It is unclear whether the anisotropy inherent in this nematicity arises from electronic spin or orbital degrees of freedom. We have studied the iron-based Mott insulators La$_{2}$O$_{2}$Fe$_{2}$O$M$$_{2}$ $M$ = (S, Se) which are structurally similar to the iron pnictide superconductors. …
We describe the local structural properties of the iron oxychalcogenides, La$_2$O$_2$Fe$_2$O$M_2$ ($M$ = S, Se), by using pair distribution function (PDF) analysis applied to total scattering data. Our results of neutron powder diffraction show that $M$ = S and Se possess similar nuclear structure at low and room temperatures. The local crystal structures were studied by investigating deviations in atomic positions and the extent of the formation of orthorhombicity. Analysis of the total scattering data suggests that buckling of the Fe$_2$O plane occurs below 100 K. The buckling may occur conc…
Magnetic order and spin dynamics in La2O2Fe2OSe2 probed by 57Fe-Moessbauer, 139La-NMR, and muon spin relaxation spectroscopy
我们提出了一个详细的本地探针研究的磁顺序在氧硫属化物La 2 O2 Fe 2 OSe 2利用57 Fe穆斯堡尔谱，139 La NMR和μ子自旋弛豫谱。该系统可作为铁砷化物和硫属化物超导体的绝缘参考系。从本地探针技术的组合，我们确定了一个非共线的磁性结构类似于Sr 2F 2Fe 2 OS 2。磁序参量的分析产生的有序温度TN = 90.1 K和β = 0.133的临界指数，这是接近的二维伊辛普适类中报道的相关氧硫族化物家庭。
Control of emergent magnetic orders in correlated electron materials promises new opportunities for applications in spintronics. For their technological exploitation, it is important to understand the role of surfaces and interfaces to other materials and their impact on the emergent magnetic orders. Here, we demonstrate for iron telluride, the nonsuperconducting parent compound of the iron chalcogenide superconductors, determination and manipulation of the surface magnetic structure by low-temperature spin-polarized scanning tunneling microscopy. Iron telluride exhibits a complex structural a…
Inelastic neutron scattering recently confirmed the theoretical prediction of a $\uparrow\uparrow\downarrow\downarrow$-magnetic state along the legs of quasi-one-dimensional (quasi-1D) iron-based ladders in the orbital-selective Mott phase (OSMP). We show here that electron-doping of the OSMP induces a whole class of novel block-states with a variety of periodicities beyond the previously reported $π/2$ pattern. We discuss the magnetic phase diagram of the OSMP regime that could be tested by neutrons once appropriate quasi-1D quantum materials with the appropriate dopings are identified.
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…
Since the discovery of pressure-induced superconductivity in the two-leg ladder system BaFe$_2X_3$ ($X$=S, Se), with the 3$d$ iron electronic density $n = 6$, the quasi-one-dimensional iron-based ladders have attracted considerable attention. Here, we use Density Functional Theory (DFT) to predict that the novel $n = 6$ iron ladder BaFe$_2$Te$_3$ could be stable with a similar crystal structure as BaFe$_2$Se$_3$. Our results also indicate that BaFe$_2$Te$_3$ will display the complex 2$\times$2 Block-type magnetic order. Due to the magnetic striction effects of this Block order, BaFe$_2$Te$_3$ …
The recent discovery of superconductivity at high pressure in the two-leg ladder compounds BaFe$_2X_3$ ($X$=S, Se) started the novel field of quasi-one-dimensional iron-based superconductors. In this publication, we use Density Functional Theory (DFT) to predict that the previously barely explored ladder compound RbFe$_2$Te$_3$ should be magnetic with a CX-type arrangement involving ferromagnetic rungs and antiferromagnetic legs, at the realistic density of $n=5.5$ electrons per iron. The magnetic state similarity with BaFe$_2$S$_3$ suggests that RbFe$_2$Te$_3$ could also become superconductin…
We present a comparative electronic structure study using DFT and various beyond-DFT (DFT+$U$, $G_0W_0$, DFT+DMFT) methods for ferromagnetic Iron (Fe) to find better approach for describing the spectral properties of correlated magnetic system. The computed value of $U$ ($W$) is $\sim$5.4 ($\sim$0.8) eV. The calculated spectra of all methods are providing good agreement with experimental spectra (ES) for peaks' positions. But, the proper line shape is only found from DFT+DMFT with correct estimation of incoherent states, which depends on $J$ and form of local Coulomb interactions. The estimati…
The recent detailed study of quasi-one-dimensional iron-based ladders, with the $3d$ iron electronic density $n = 6$, has unveiled surprises, such as orbital-selective phases. However, similar studies for $n=6$ iron chains are still rare. Here, a three-orbital electronic Hubbard model was constructed to study the magnetic and electronic properties of the quasi-one-dimensional $n=6$ iron chain Ce$_2$O$_2$FeSe$_2$, with focus on the effect of doping. Specifically, introducing the Hubbard $U$ and Hund $J_{H}$ couplings and studying the model via the density matrix renormalization group, we report…
We have performed x-ray magnetic circular dichroism (XMCD) measurements on the iron-based superconductor Sr$_2$VFeAsO$_{3-δ}$ to study the origin of weak ferromagnetism (WFM) reported for this compound. While Fe 3$d$ electrons show a magnetic response similar to the other iron pnictides, signals from V 3$d$ electrons remain finite at zero magnetic field and may be responsible for the WFM.
Quasi-one-dimensional iron chalcogenides possess various magnetic states depending on the lattice distortion, electronic correlations, and presence of defects. We present neutron diffraction and inelastic neutron scattering experiments on the spin ladder compound BaFe$_{2-δ}$S$_{1.5}$Se$_{1.5}$ with $\sim$6% iron vacancies. The data reveal that long-range magnetic order is absent, while the characteristic magnetic excitations that correspond to both the stripe- and block-type antiferromagnetic correlations are observed. First-principles calculations support the existence of both stripe and blo…
Recent experiments in iron pnictide superconductors reveal that, as the putative magnetic quantum critical point is approached, different types of magnetic order coexist over a narrow region of the phase diagram. Although these magnetic configurations share the same wave-vectors, they break distinct symmetries of the lattice. Importantly, the highest superconducting transition temperature takes place close to this proliferation of near-degenerate magnetic states. In this paper, we employ a renormalization group calculation to show that such a behavior naturally arises due to the effects of spi…
Investigation of the crystal and magnetic structures of the trigonal multiferroic iron-boracite Fe3B7O13(OH)
本文用中子衍射方法研究了三方晶系铁硼石Fe_3B_7O_（13）X（X = OH）的晶体结构和磁性。中子衍射使我们能够找到羟基的氢原子，并确定磁性基态的这个成员的多铁性硼酸盐家庭。没有证据表明磁有序状态的单斜畸变。磁对称性允许磁电和铁电性质。TN的氮平衡温度为4.86（4）K，证实了硼质岩中TN从X = I > Br > Cl > OH降低的总趋势。令人惊讶的是，虽然Fe 3 B 7 O 13 OH在Fe 3 B 7 O 13 X系列中表现出与$|θ/T_N| = 5.6$的最大挫折，但使用中子衍射未发现磁矩的降低。
