Fe Chains Research Articles

FePd2Te2: An Anisotropic Two-Dimensional Ferromagnet with One-Dimensional Fe Chains.

Two-dimensional (2D) magnets have attracted significant attention in recent years due to their importance in the research on both fundamental physics and spintronic applications. Here, we report the discovery of a new ternary compound FePd2Te2. It features a layered quasi-2D crystal structure with 1D Fe zigzag chains extending along the b-axis in the cleavage plane. Single crystals of FePd2Te2 with centimeter size could be grown. Density functional theory calculations, mechanical exfoliation, and atomic force microscopy on these crystals reveal that they are 2D materials that can be thinned down to ∼5 nm. Magnetic characterization shows that FePd2Te2 is an easy-plane ferromagnet with TC ∼ 183 K and strong in-plane uniaxial magnetic anisotropy. Magnetoresistance and the anomalous Hall effect demonstrate that ferromagnetism could be maintained in FePd2Te2 flakes with large coercivity. A crystal twinning effect is observed by scanning tunneling microscopy which makes the Fe chains right angle bent in the cleavage plane and creates an intriguing spin texture. Besides, a large electronic specific heat coefficient of up to γ ∼ 32.4 mJ mol-1 K-2 suggests FePd2Te2 is a strongly correlated metal. Our results show that FePd2Te2 is a correlated anisotropic 2D magnet that may attract multidisciplinary research interests.

Er-driven incommensurate to commensurate magnetic phase transition of Fe in the spin-chain compound BaErFeO4

Magnetic phase transitions and structures of the spin-chain compound BaErFeO4 were investigated by measurements of magnetic properties (specific heat, magnetic susceptibility) and neutron diffraction. The lattice geometry of the orthorhombic crystal structure (space group ) of the BaRFeO4 compounds (R=Dy–Yb, Y) supports frustrations which lead to multiple magnetic phase transitions with complex magnetic structures. BaErFeO4 undergoes three successive magnetic phase transitions at TN1=49K, TN2=33.4K, and TN3=3.4K. In contrast with the previously investigated BaRFeO4 (R=Y, Tm, Yb) compounds, all with incommensurate magnetic propagation vectors k1=(0,0,kz), BaErFeO4 is the first member in this series that shows a phase transition from an incommensurate (k1 below TN1) to a commensurate magnetic structure with k2=(12,0,12) below TN2. In the crystal structure, all magnetic ions (Fe1, Fe2, Er1, and Er2) are part of chains propagating along the b axis. Below TN1, strong antiferromagnetic (AFM) Fe-Fe spin-exchange coupling between square pyramidal (Fe1) and octahedral (Fe2) centers generates a collinear AFM structure with a constant size of the ordered Fe moments and a constant magnetic phase inside each chain of Fe3+ cations. Exchange coupling between the Fe chains is much weaker. At TN2, 3d−4f exchange interactions induce an ordered moment at the Er3+ ions, which results in a change of the direction of the ordered Fe moments from the b direction (above TN2) to inside the ac plane (below TN2) and a change from an incommensurate (k1 above TN2) to a commensurate (k2 below TN2) AFM structure. Toward lower temperature, 4f−4f exchange interactions become stronger and create at TN3 a constant magnetic phase inside each chain of Er3+ cations. At TN2 and TN3, the magnetic susceptibility shows sharp decreases that coincide with large increases of the correlation length of the magnetic structure. The unique magnetic structures of BaErFeO4 are compared with those of other BaRFeO4 compounds by considering experimental and theoretical aspects. ©2024 American Physical Society 2024 American Physical Society

Ground and excited states of the finite-size Fe chains on Pt(664) surface

Ground and excited states of the finite-size Fe chains on Pt(664) surface

Isotopic dependence of (n,α) reaction cross sections for Fe and Sn nuclei

The (n,α) reactions play an important role for the energy generation and the synthesis of chemical elements in the stars, as well as for nuclear engineering and medical applications. The aim of this study is to explore the evolution of (n,α) reactions in Fe and Sn isotope chains in order to assess the cross section properties with the increase of neutron number in target nucleus, and to make a comparison with other relevant neutron induced reactions. The cross section calculations are based on the statistical Hauser-Feshbach and exciton models in TALYS nuclear reaction code, using global optical model potential that is additionally adjusted by the (n,α) cross section data for 54Fe and 118Sn. The calculations of (n,α) reactions in Fe and Sn isotopes provide the insight into their isotopic dependence and properties over the complete relevant range of neutron energies. The cross sections result in pronounced maxima at lower-mass isotopes, and rather strong decrease for neutron-rich nuclei consistent with the reduction of the reaction Q-value and increased contributions from other exit channels from compound nucleus. The analysis of the Maxwellian averaged cross sections at temperatures in stellar environment shows that the (n,α) reactions have significant contributions for low-mass Fe isotopes, that is opposite than for Sn isotopes. For both neutron rich isotopes γ and neutron emissions dominate, with their interplay depending on the temperature involved.

The High-Pressure Phase Transition in Jamesonite: A Single-Crystal Synchrotron X-ray Diffraction Study

The high-pressure behavior of jamesonite (FePb4Sb6S14, a = 4.08(3) Å, b = 19.08(3) Å, c = 15.67(3) Å, β= 91.89°, space group P21/c) has been investigated using in situ HP synchrotron X-ray single-crystal diffraction up to ~17 GPa with a diamond anvil cell under hydrostatic conditions. Results of the volume isothermal equation of state (EoS), determined by fitting the P-V data with a third-order Birch–Murnaghan (BM) EoS, are V0 = 1207.1(4) Å3, K0 = 36(1) GPa and K’ = 5.7(7). At high pressure, jamesonite undergoes a phase transition to an orthorhombic structure with a Pmcb space group (β-jamesonite). The analysis of β-jamesonite’s compressibility up to 16.6 GPa, studied by fitting the data with a second-order BM-EoS, gives V0 = 1027(2) Å3, K0 = 74(2) GPa. The comparison of the structural refinements at different pressures indicates that Fe, Pb and Sb do not change their coordination number over the whole investigated P range, respectively, 6 for Fe, 7 and 8 for Pb and 5 + 2 for Sb. However, a significant change occurs on the orientation of Sb lone electron pairs upon the phase transition in accordance with the change in symmetry. Furthermore, a discontinuity in the Fe chain evolution at the transition pressure is observed.

Dynamical Stability and Physical Properties of Fe Dihalide Nanowires

AbstractAn extensive first‐principles and atomistic Monte Carlo study on isolated Fe ( = F, Cl, Br, I) nanowires is presented. The structural properties of the Fe chains are determined and compared with their bulk structures. The results indicate that in the lowest energy configuration, the wires crystalize in a system that belongs to the space group (No. 131, Z = 2, point group ), with antiferromagnetic arrangement. The stability is determined by calculating the phonon frequencies in the whole Brillouin zone within the supercell approach. The relative stability of the periodic chains is also determined by calculating the elastic properties and comparing them with bulk cases. The band structure, the density of states, the magnetic properties, the anisotropy energy, and topological analysis, performed with the Quantum Theory of Atoms in Molecules approach, are also reported and discussed. The results support the idea that these Fe nanowire systems are promising materials for practical applications, like lithium‐ion batteries.

Cycloidal spiral magnetic structures in the spin-chain compounds BaRFeO4 ( R=Yb and Tm): Ordered Yb versus partly ordered Tm

$\mathrm{Ba}R\mathrm{Fe}{\mathrm{O}}_{4}$ compounds containing magnetic rare-earth ions ($R=\mathrm{Yb}$, Tm) were prepared by a conventional solid-state method in air. We present detailed measurements of magnetic properties (specific heat, magnetic susceptibility) to demonstrate the presence of three successive magnetic phase transitions (at ${T}_{\mathrm{N}1}$, ${T}_{\mathrm{N}2}$, and ${T}_{3}$) in both compounds and employed neutron diffraction to determine the magnetic structures. Both compounds are isostructural (orthorhombic space group $Pnma$) and magnetic ions form rings and chains along the $b$ direction. All magnetic structures are incommensurate with a propagation vector $\mathbf{k}=(0,\phantom{\rule{0.28em}{0ex}}0,\phantom{\rule{0.28em}{0ex}}{k}_{z})$. Magnetic ordering of ${\mathrm{Fe}}^{3+}$ ions occurs at ${T}_{\mathrm{N}1}$ and ${T}_{\mathrm{N}2}$, where two different irreducible representations (irreps) order. Below ${T}_{\mathrm{N}1}$, there is a collinear spin-density wave with ordered ${\mathrm{Fe}}^{3+}$ moments along the chain direction ($b$ axis). Below ${T}_{\mathrm{N}2}$, this component remains stable and an additional component inside the $ac$ plane appears. Each Fe chain adopts a collinear antiferromagnetic structure with a constant magnetic phase. The two Fe rings in the unit cell have a different chirality and a noncollinear coupling. The mixing of two irreps leads to a cycloidal spiral magnetic structure that allows spin-induced ferroelectric polarization at ${T}_{\mathrm{N}2}$. With the presence of modulated components both perpendicular and along the propagation vector $\mathbf{k}$, the magnetic structure can be viewed as a sum of a helix and a cycloid structure. For ${\mathrm{BaTmFeO}}_{4}$, the magnetic structure has a larger cycloidal contribution and the dielectric constant \ensuremath{\epsilon} exhibits a small peak at ${T}_{\mathrm{N}2}$. ${\mathrm{Yb}}^{3+}$ moments order at ${T}_{3}$ with each Yb chain having a constant magnetic phase and a collinear antiferromagnetic structure stabilized by $4f\ensuremath{-}4f$ electron-exchange interactions. In contrast, no constant magnetic phase is observed at the Tm chains. Below ${T}_{3}$, magnetic order of Tm2 ions is induced by $3d\ensuremath{-}4f$ electron-exchange interactions and Tm1 ions remain disordered down to the lowest measured temperature $T=1.6\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ due to frustration of magnetic exchange interactions. The obtained magnetic structures are compared with those of ${\mathrm{BaYFeO}}_{4}$.

An antiferromagnetic semiconducting FeCN2 monolayer with a large magnetic anisotropy and strong magnetic coupling.

Two-dimensional antiferromagnetic (AFM) materials with an intrinsic semiconductivity, a high critical temperature, and a sizable magnetic anisotropy energy (MAE) have attracted extensive attention because they show promise for high-performance spintronic nanodevices. Here, we have identified a new FeCN2 monolayer with a unique zigzag Fe chain through first-principles swarm structural search calculations. It is an AFM semiconductor with a direct band gap of 2.04 eV, a Néel temperature (TN) of 176 K, and a large in-plane MAE of 0.50 meV per Fe atom. More interestingly, the intrinsic antiferromagnetism, contributed by the strong magnetic coupling of neighbouring Fe ions, can be maintained under the external biaxial strains. A large cohesive energy and high dynamical stability favor synthesis and application. Therefore, these fascinating properties of the FeCN2 monolayer make it a promising nanoscale spintronic material.

Effect of magnesium treatment on microstructure and property of H13 die steel during EAF-LF-VD-CC steelmaking process

Due to the advantages of Mg on inclusions and carbides in H13 steel, Mg wire was added into industrial ladle after VD process to replace traditional Ca treatment in this paper, which is of great significance for industrial production of H13 steel. This paper focuses on the effects of Mg treatment and traditional Ca treatment on the inclusions, carbides, microstructure and mechanical properties in H13 steel. The results show that feeding Mg wire during EAF→ LF→ VD → CC steelmaking process can ensure the submerged nozzle not being blocked under the condition of continuous casting 15 heats of steel ladle, which means feeding Ca wire can be replaced with Mg wire from the aspect of steelmaking production. The primary carbides in Mg treatment steel are mainly precipitated with MgO or MgAl2O4 as the cores and small in size, while the primary carbides in Ca treatment steel are almost large-size carbides without core. The samples taken from the intermediate ladle show that the primary carbide types are all V-rich, Mo-rich and V–Mo-rich composite, and the size of primary carbides in Mg treatment steel is much smaller than that in Ca treatment steel. Adding Mg is helpful to improve the equiaxed crystal rate of continuous casting ingot. The annealed hot rolling samples show that Mg treatment could interrupt the M23C6 (M = Cr, Fe) chain carbides distributed along the grain boundary. The impact test shows that the dimple fracture surface become small and deep after adding Mg, which improves impact toughness significantly.

Magnetic ground state of supported monatomic Fe chains from first principles

A new computational scheme is presented based on a combination of the conjugate gradient and the Newton–Raphson method to self-consistently minimize the energy within local spin-density functional theory, thus to identify the ground state magnetic order of a finite cluster of atoms. The applicability of the new ab initio optimization method is demonstrated for Fe chains deposited on different metallic substrates. The optimized magnetic ground states of the Fe chains on Rh(111) are analyzed in details and a good comparison is found with those obtained from an extended Heisenberg model containing first principles based interaction parameters. Moreover, the effect of the different bilinear spin–spin interactions in the formation of the magnetic ground states is monitored. In case of Fe chains on Nb(110) spin-spiral configurations with opposite rotational sense are found as compared to previous spin-model results which hints on the importance of higher order chiral interactions. The wavelength of the spin-spiral states of Fe chains on Re(0001) was obtained in good agreement with scanning tunneling microscopy experiments.

Quantum spins and hybridization in artificially-constructed chains of magnetic adatoms on a superconductor

Magnetic adatom chains on surfaces constitute fascinating quantum spin systems. Superconducting substrates suppress interactions with bulk electronic excitations but couple the adatom spins to a chain of subgap Yu-Shiba-Rusinov (YSR) quasiparticles. Using a scanning tunneling microscope, we investigate such correlated spin-fermion systems by constructing Fe chains adatom by adatom on superconducting NbSe2. The adatoms couple entirely via the substrate, retaining their quantum spin nature. In dimers, we observe that the deepest YSR state undergoes a quantum phase transition due to Ruderman-Kittel-Kasuya-Yosida interactions, a distinct signature of quantum spins. Chains exhibit coherent hybridization and band formation of the YSR excitations, indicating ferromagnetic coupling. Longer chains develop separate domains due to coexisting charge-density-wave order of NbSe2. Despite the spin-orbit-coupled substrate, we find no signatures of Majoranas, possibly because quantum spins reduce the parameter range for topological superconductivity. We suggest that adatom chains are versatile systems for investigating correlated-electron physics and its interplay with topological superconductivity.

Improved kinetic Monte Carlo models for computational and analytical investigations of the magnetic properties of finite-size atomic chains

Two improved kinetic Monte Carlo (kMC) models for investigations of the magnetic properties of finite-size atomic chains are presented. These models take into account the possible noncollinearity of magnetic moments. The spontaneous remagnetization of ferromagnetic Co chains on the Pt(997) surface and antiferromagnetic Fe chains on the surface is investigated in the framework of our models. The results are compared with the results of the simple kMC model. It is also shown that a single domain-wall approximation can be successfully used to estimate the reversal time of the magnetization. Therefore, the improved kMC models can be used for analytical calculations as well as for computer simulations.

Evolution of β -decay half-lives in stellar environments

$\ensuremath{\beta}$-decay properties of nuclei are investigated within the relativistic nuclear energy density functional framework by varying the temperature and density, conditions relevant to the final stages of stellar evolution. Both thermal and nuclear pairing effects are taken into account in the description of nuclear properties and in the finite-temperature proton-neutron relativistic quasiparticle random-phase approximation (FT-PNRQRPA) to calculate the relevant allowed and first-forbidden transitions in the $\ensuremath{\beta}$ decay. The temperature and density effects are studied on the $\ensuremath{\beta}$-decay half-lives at temperatures $T=0$--$1.5\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ and at densities $\ensuremath{\rho}{Y}_{e}={10}^{7}\phantom{\rule{4pt}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$ and ${10}^{9}\phantom{\rule{4pt}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$. The relevant Gamow-Teller transitions are also investigated for Ti, Fe, Cd, and Sn isotopic chains at finite-temperatures. We find that the $\ensuremath{\beta}$-decay half-lives increase with increasing density $\ensuremath{\rho}{Y}_{e}$, whereas half-lives generally decrease with increasing temperature. It is shown that the temperature effects decrease the half-lives considerably in nuclei with longer half-lives at zero temperature, while only slight changes for nuclei with short half-lives are obtained. We also show the importance of including the de-excitation transitions in the calculation of the $\ensuremath{\beta}$-decay half-lives at finite-temperatures. Comparing the FT-PNQRPA results with the shell-model calculations for $pf$-shell nuclei, a reasonable agreement is obtained for the temperature dependence of $\ensuremath{\beta}$-decay rates. Finally, large-scale calculations of $\ensuremath{\beta}$-decay half-lives are performed at temperatures ${T}_{9}(\text{K})=5$ and ${T}_{9}(\text{K})=10$ and densities $\ensuremath{\rho}{Y}_{e}={10}^{7}$ and ${10}^{9}\phantom{\rule{4pt}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$ for even-even nuclei in the range $8\ensuremath{\le}Z\ensuremath{\le}82$, relevant for astrophysical nucleosynthesis mechanisms.

Nanoresonator Enhancement of Majorana-Fermion-Induced Slow Light in Superconducting Iron Chains.

We theoretically investigate Fano resonance in the absorption spectrum of a quantum dot (QD) based on a hybrid QD-nanomechanical resonator (QD–NR) system mediated by Majorana fermions (MFs) in superconducting iron (Fe) chains. The absorption spectra exhibit a series of asymmetric Fano line shapes, which are accompanied by the rapid normal phase dispersion and induce the optical propagation properties such as the slow light effect under suitable parametric regimes. The results indicated that the slow light induced by MFs can be obtained under different coupling regimes and different detuning regimes. Moreover, we also investigated the role of the NR, and the NR behaving as a phonon cavity enhances the slow light effect.

Novel Fluorine-Pillared Metal-Organic Framework for Highly Effective Lithium Enrichment from Brine.

The continuously developing lithium battery market makes seeking a reliable lithium supply a top priority for technology companies. Although metal-organic frameworks have been extensively researched as adsorbents owing to their exceptional properties, lithium adsorption has been scarcely investigated. Herein, we prepared a novel cuboid rod-shaped three-dimensional framework termed TJU-21 composed of fluorine-pillared coordination layers of Fe-O inorganic chains and benzene-1,3,5-tricarboxylate (BTC) linkages. Besides thermal and chemical robustness, a remarkably high lithium uptake of about 41 mg·g-1 was observed on TJU-21 as a fast-spontaneous endothermic process. Single-crystal X-ray diffraction demonstrated that the adsorbed lithium was located in the cavity symmetrically assembled by iron sites and organic ligands between adjacent layers, while another kind of cavity in the framework circled by Fe-O-Fe-O-Fe-O-Fe chains and shared BTC linkages was occupied by hydrogen-bonded water molecules. Lithium adsorption resulted in decreased curviness of the coordination layers, and the binding energy change at O 1s as well as the increased Fe 2p peak, suggested potential interaction with iron sites. The practicability of TJU-21 as a lithium adsorbent was further proved by the considerable capacity and selectivity in simulated salt brines with excellent reusability.

Coupling between antiferromagnetic and spin-glass orders in the quasi-one-dimensional iron tellurideTaFe1+xTe3(x=0.25)

Understanding the interplay among different magnetic exchange interactions and its physical consequences, especially in the presence of itinerant electrons and disorders, remains one of the central themes in condensed matter physics. In this vein, the coupling between antiferromagnetic and spin glass orders may lead to large exchange bias, a property of potential broad technological applications. In this article, we report the coexistence of antiferromagnetic order and spin glass behaviors in a quasi-one-dimensional iron telluride TaFe$_{1+x}$Te$_3$ ($x$=0.25). Its antiferromagnetism is believed to arise from the antiferromagnetic interchain coupling between the ferromagnetically aligned FeTe chains along the $b$-axis, while the spin glassy state stems from the disordered Fe interstitials. This dichotomic role of chain and interstitial sublattices is responsible for the large exchange bias observed at low temperatures, with the interstitial Fe acting as the uncompensated moment and its neighboring Fe chain providing the source for its pinning. This iron-based telluride may thereby represent a new paradigm to study the large family of transition metal chalcogenides whose magnetic order or even the dimensionality can be tuned to a large extent, forming a fertile playground to manipulate or switch the spin degrees of freedom thereof.

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe III 4 Fe II 4 } Cubes

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe ^III ₄ Fe ^II ₄ } Cubes

Electronic and Magnetic Properties of Building Blocks of Mn and Fe Atomic Chains on Nb(110).

We present results for the electronic and magnetic structure of Mn and Fe clusters on Nb(110) surface, focusing on building blocks of atomic chains as possible realizations of topological superconductivity. The magnetic ground states of the atomic dimers and most of the monatomic chains are determined by the nearest-neighbor isotropic interaction. To gain physical insight, the dependence on the crystallographic direction as well as on the atomic coordination number is analyzed via an orbital decomposition of this isotropic interaction based on the spin-cluster expansion and the difference in the local density of states between ferromagnetic and antiferromagnetic configurations. A spin-spiral ground state is obtained for Fe chains along the [] direction as a consequence of the frustration of the isotropic interactions. Here, a flat spin-spiral dispersion relation is identified, which can stabilize spin spirals with various wave vectors together with the magnetic anisotropy. This may lead to the observation of spin spirals of different wave vectors and chiralities in longer chains instead of a unique ground state.

Coupling of Yu-Shiba-Rusinov states in one-dimensional chains of Fe atoms on Nb(110)

The hybridization of Yu-Shiba-Rusinov states in dimers of magnetic impurities leads to molecular-like bonding and antibonding modes. In many-impurity systems, the interaction gives rise to YSR bands and can even result in the formation of a topologically non-trivial superconducting state, characterized by Majorana fermions at the edges of the system. To obtain a more detailed understanding of these interactions, we investigate the coupling of YSR states in short one-dimensional Fe chains on clean Nb(110). We observe a splitting of the single-atom YSR peaks into multiple states with even or odd spatial symmetry and identify a peculiar dependence of the even and odd states' energy position on the chain length.

In-situ regrowth constructed magnetic coupling 1D/2D Fe assembly as broadband and high-efficient microwave absorber

Magnetic material performance critically depends on its anisotropic behavior, however, the regulate strategy is still in lack. Herein, a novel 1D/2D anisotropic assembly of two-dimension (2D) magnetic Fe nanosheets supported on one-dimension (1D) Fe chain is successfully constructed as an excellent microwave absorber. By a controllable in-situ regrowth and subsequent reduction strategy, 2D Fe nanosheets radiating out the 1D Fe chain along its axis orientation are successfully converted from an intermediate γ-FeOOH phase. 1D axial Fe chains are self-assembled from isolated Fe nanospheres by the magnetic dipolar interactions. The multi-dimensional 1D/2D Fe exhibits an outstanding absorption performance with reflection loss of −57.3 dB and ultra-wide effective bandwidth of 11.5 GHz (1.9 mm). Integrated large planar anisotropy of 2D Fe nanosheets with anisotropic field of 1D Fe chains, such a hierarchical structure endows the assembly with strong anisotropy for magnetic response enhancement. Reinforced by the ultrathin magnetic nanosheets with high specific surface area, high-density magnetic flux lines construct the large-scale 3D coupling nets, which is confirmed by electron holography. The hierarchical chains cross-link with each other and form 3D conductive networks for enhancing dielectric loss. This finding might provide a novel idea on the design of high-performance microwave absorbers.