Fe Chains Research Articles

Observation of two types of magnetization relaxation in a weakly correlated antiferromagnetic chain of MnIII2 single-molecule magnets

A Mn(III)(2)Fe(II) chain with a [-Mn(III)-(O(Ph))(2)-Mn(III)-ON-Fe(II)-NO-] repeat unit was synthesized via the assembling reaction of Mn(III) salen-type dimers and Fe(II) pyridyloximate complexes, where the -(O(Ph))- and -ON- bridges represent a biphenolate bridge and an oximate bridge, respectively. The bulky counter anions, BPh(4)(-), which surround the chain to form a zeolite-like brick wall, successfully isolate the chains from a magnetic point of view. This compound is isostructural with Mn(2)Ni-BPh(4), which is an SCM with S(T) = 3 (H. Miyasaka, A. Saitoh, M. Yamashita and R. Clérac, Dalton Trans., 2008, 2422). Because the Fe(II) unit is diamagnetic, the Mn(III) dimer, which has the potential to be a single-molecule magnet (SMM), is nearly magnetically isolated, although a weak antiferromagnetic interaction with J/k(B)≈-0.1 K is perturbed between the Mn(III) dimers with S(T) = 4 via the Fe(II) unit. Ac susceptibility data shows that two types of relaxation of the magnetization are present, which are attributed to SMM and chain relaxations.

Magnetic properties of Fe chains on Cu2N/Cu(100): A density functional theory study

We present a density functional study of the magnetic properties of Fe adatoms on Cu2N/Cu(100) surface. The magnetic anisotropy energies of a single Fe atom are in excellent agreement with the available experiments. Our results for the spin densities and exchange coupling strengths for Fe dimer and trimer establish antiferromagnetic configuration to be the ground state due to predominant superexchange interaction mediated by nitrogen atoms in this system.

Catena-Poly[(E)-4,4′-(ethane-1,2-diyl)dipyridinium [[bis(thiocyanato-κN)ferrate(II)]-di-μ-thiocyanato-κ2N:S;κ2S:N

In the crystal structure of the title compound, {(C12H14N2)[Fe(NCS)4]}n, the iron(II) cation is coordinated by four N-bonded and two S-bonded thio­cyanate anions in a distorted octa­hedral coordination mode. The asymmetric unit consists of half an iron(II) cation and half a protonated (E)-4,4′-(ethane-1,2-di­yl)dipyridinium dication, each located on a centre of inversion. In addition, there are two thio­cyanate anions in general positions. The crystal structure consists of Fe—(NCS)2—Fe chains in which each iron(II) cation is additionally coordinated by two terminal N-bonded thio­cyanate anions. Non-coordinating dipyridinium dications are present between the thiocyanatoferrate(II) chains and are connected to the anions via N—H⋯N and N—H⋯S hydrogen-bond interactions.

Electronic and magnetic properties of Fe, Co and Ni atomic chains encapsulated in BN nanotube bundle

The electronic and magnetic properties of the (6, 6) BN nanotube bundle in the presence of the Fe, Co and Ni atomic chains have been studied by the first principles calculations in the framework of the density functional theory (DFT). Results show that the our systems have ferromagnetic properties. All TM@(6, 6) BNNTs bundle systems are formed endothermically. The spin polarization and the magnetic moment of the system are depend on the position and type of the transition metal atomic chains. The Ni atomic chain has maximum spin polarization and maximum stability.

Group 6 Complexes with Iron and Zinc Heterometals: Understanding the Structural, Spectroscopic, and Electrochemical Properties of a Complete Series of MM···M′ Compounds

Binuclear quadruply bonded complexes Cr(2)(dpa)(4) (1, dpa = 2,2'-dipyridylamide), Mo(2)(dpa)(4) (2), and W(2)(dpa)(4) (3) react with anhydrous FeCl(2), yielding heterometallic compounds CrCrFe(dpa)(4)Cl(2) (4), MoMoFe(dpa)(4)Cl(2) (5), and WWFe(dpa)(4)Cl(2) (6). These molecules are structurally similar, having a linear M≡M···Fe chain that is axially capped by chloride ions and is equatorially supported by the helically twisted dpa ligands. A structurally related zinc analog, CrCrZn(dpa)(4)Cl(2) (7), can be prepared upon metalation of 1 with ZnCl(2). This reaction also persistently produces a 2:1 adduct of ZnCl(2) with 1, [Cr(2)(dpa)(4)](ZnCl(2))(2) (8), which is in equilibrium with 7 and has the two zinc ions bound externally to the Cr(2) core and axial bridging chloro ligands attached to each Cr ion. The sole isolable product of the addition of ZnCl(2) to 3 is a 1:1 adduct, [W(2)(dpa)(4)]ZnCl(2) (9). The structurally related chain complexes 4, 5, 6, and 7 are characterized by X-ray crystallography, UV-vis spectroscopy, cyclic voltammetry, and (57)Fe Mössbauer spectroscopy for the iron complexes in order to gain insights into the nature of heterometallic interactions, electronic excited states, and redox properties of these compounds, which have implications for all other M≡M···M' molecules. Additionally, NMR spectroscopy has been used to gain insight into the mechanism of the metalation of 1 by Zn(II).

Spin-polarized transport properties of Fe atomic chain adsorbed on zigzag graphene nanoribbons

The spin-polarized transport properties of Fe atomic chain adsorbed on zigzag graphene nanoribbons (ZGNRs) are investigated using the density-functional theory in combination with the nonequilibrium Green's function method. We find that the Fe chain has drastic effects on spin-polarized transport properties of ZGNRs compared with a single Fe atom adsorbed on the ZGNRs. When the Fe chain is adsorbed on the centre of the ZGNR, the original semiconductor transforms into metal, showing a very wide range of spin-polarized transport. Particularly, the spin polarization around the Fermi level is up to 100%. This is because the adsorbed Fe chain not only induces many localized states but also has effects on the edge states of ZGNR, which can effectively modulate the spin-polarized transports. The spin polarization of ZGNRs is sensitive to the adsorption site of the Fe chain. When the Fe chain is adsorbed on the edge of ZGNR, the spin degeneracy of conductance is completely broken. The spin polarization is found to be more pronounced because the edge state of one edge is destroyed by the additional Fe chain. These results have direct implications for the control of the spin-dependent conductance in ZGNRs with the adsorption of Fe chains.

Magnetic anisotropy and spin-spiral wave in V, Cr and Mn atomic chains on Cu(0 0 1) surface: first principles calculations

Recent ab intio studies of the magnetic properties of all 3d transition metal (TM) freestanding atomic chains have predicted that these nanowires could have a giant magnetic anisotropy energy (MAE) and might support a spin-spiral structure, thereby suggesting that these nanowires would have technological applications in, e.g. high-density magnetic data storage. In order to investigate how the substrates may affect the magnetic properties of the nanowires, here we systematically study V, Cr and Mn linear atomic chains on a Cu(0 0 1) surface based on the density functional theory with the generalized gradient approximation. We find that V, Cr and Mn linear chains on the Cu(0 0 1) surface still have a stable or metastable ferromagnetic state. However, the ferromagnetic state is unstable against the formation of a noncollinear spin-spiral structure in the Mn linear chains and also the V linear chain on the atop sites on the Cu(0 0 1) surface, due to the frustrated magnetic interactions in these systems. Nonetheless, the presence of the Cu(0 0 1) substrate does destabilize the spin-spiral state already present in the freestanding V linear chain and stabilizes the ferromagnetic state in the V linear chain on the hollow sites on Cu(0 0 1). When spin–orbit coupling (SOC) is included, the spin magnetic moments remain almost unchanged due to the weakness of SOC in 3d TM chains. Furthermore, both the orbital magnetic moments and MAEs for V, Cr and Mn are small, in comparison with both the corresponding freestanding nanowires and also the Fe, Co and Ni linear chains on the Cu(0 0 1) surface.

Noncollinear magnetism in freestanding and supported monatomic Mn chains

Using first-principles calculations, we study the occurrence of noncollinear magnetic order in monatomic Mn chains. First, we focus on freestanding Mn chains and demonstrate that they exhibit a pronounced noncollinear ground state in a large range of interatomic distances between atoms in the chain. By artificially varying the atomic number of Mn we investigate how the magnetic ground state is influenced by alloying the Mn chains with Fe and Cr. With increasing number of $3d$ electrons we find a smooth transition in the magnetic phase space starting from an antiferromagnetic state for pure Cr chains through a regime of noncollinear ground states for Mn-rich chains to a ferromagnetic solution approaching the limit of pure Fe chains. Second, we investigate the magnetism in supported Mn chains on the (110) surfaces of Cu, Pd, and Ag. We show that even a weak chain-surface hybridization is sufficient to dramatically change the magnetic coupling in the chain. Nevertheless, while we observe that Mn chains are antiferromagnetic on Pd(110), a weak noncollinear magnetic order survives for Mn chains on Cu(110) and Ag(110) a few meV in energy below the antiferromagnetic solution. We explain the sensitive dependence of the exchange interaction in Mn chains on the interatomic distance, chemical composition, and their environment based on the competition between the ferromagnetic double exchange and the antiferromagnetic kinetic exchange mechanism. Finally, we perform simulations which predict that the noncollinear magnetic order of Mn chains on Cu(110) and Ag(110) could be experimentally verified by spin-polarized scanning tunneling microscopy.

Ab initiostudies of spin-spiral waves and exchange interactions in3dtransition metal atomic chains

The total energy of the transverse spin-spiral wave as a function of the wave vector for all $3d$ transition metal atomic chains has been calculated within ab initio density functional theory with the generalized gradient approximation. It is predicted that at the equilibrium bond length, the V, Mn, and Fe chains have a stable spin-spiral structure, while the magnetic ground state of the Cr, Co, and Ni chains remains collinear. Furthermore, all the exchange interaction parameters of the $3d$ transition metal chains are evaluated by using the calculated energy dispersion relations of the spin-spiral waves. Interestingly, it is found that the magnetic couplings in the V, Mn, and Cr chains are frustrated (i.e., the second near-neighbor exchange interaction is antiferromagnetic), and this leads to the formation of the stable spin-spiral structure in these chains. The spin-wave stiffness constant of these $3d$ metal chains is also evaluated and is found to be smaller than its counterpart in bulk systems. The upper limit (on the order of 100 Kelvins) of the possible magnetic phase transition temperature in these atomic chains is also estimated within the mean-field approximation. The electronic band structure of the spin-spiral structures have also been calculated. It is hoped that the interesting findings here of the stable spin-spiral structure and frustrated magnetic interaction in the $3d$ transition metal chains will stimulate further theoretical and experimental research in this field.

First principles study on spin and orbital magnetism of 3d transition metal monatomicnanowires (Mn, Fe and Co)

We have demonstrated the electronic structure and magnetic properties of 3d transitionmetal nanowires (Mn, Fe and Co) in the framework of relativistic density functionaltheory. The equilibrium bond lengths were optimized using the generalized gradientapproximation. In a full relativistic regime individual spin and orbital moments inducedfrom spin polarization via spin–orbit coupling were calculated. In order to get an upperestimate for orbital moments, we used an orbital polarization correction to ourexchange–correlation functional. We found that the orbital magnetic moments of Fe and Colinear chains are strongly enhanced in the presence of an orbital polarization correction. Wehave calculated the exchange coupling parameters between two nearest-neighbormagnetic atoms according to a Heisenberg-like model in the presence of the orbitalpolarization correction. We found that the Co and Fe nanowires behave like aferromagnetic linear chain whereas a Mn monatomic nanowire remains antiferromagnetic.

Uniaxial magnetic anisotropy of quasi-one-dimensional Fe chains on Pb/Si: A Monte Carlo simulation

Magnetic behaviors of Fe nanowires grown on 4° miscut Si(111) substrate with Pb buffer layers have been investigated by means of Monte Carlo method. A simple model is constructed, in which the Fe chains are assumed to be assemblies of single domain Fe nanoclusters with magnetostatic energy and exchange coupling energy. The coverage dependence of the magnetic ordering temperature TC of the system is discussed. By accurately calculating the magnetostatic energy of the Fe chains, the simulated results are in agreement with the experimental ones measured by in situ surface magneto-optical Kerr effect. In addition to the magnetostatic energy, the exchange coupling between the overlapping islands is also responsible for the ferromagnetic ordering of high coverage Fe chains at room temperature. Our model was able to predict the essential features of the system.

Catena-Poly[(E)-4,4′-(ethene-1,2-diyl)dipyridinium [[bis(thiocyanato-κN)ferrate(II)]-di-μ-thiocyanato-κ2N:S;κ2S:N

In the title compound, {(C12H12N2)[Fe(NCS)4]}n, each FeII cation is coordinated by four N-bonded and two S-bonded thio­cyanate anions in an octa­hedral coordination mode. The asymmetric unit consists of one FeII cation, located on a center of inversion, as well as one protonated (E)-4,4′-(ethene-1,2-di­yl)dipyridinium dication and two thio­cyanate anions in general positions. The crystal structure consists of Fe—(NCS)2—Fe chains extending along the a axis, in which two further thio­cyanate anions are only terminally bonded via nitro­gen. Non-coordinating (E)-4,4′-(ethene-1,2-di­yl)dipyrid­inium cations are found between the chains.

An ab initio study of the magnetic and electronic properties of Fe, Co, and Ni nanowires on Cu(001) surface

Magnetism at the nanoscale has been a very active research area in the past decades, because of its novel fundamental physics and exciting potential applications. We have recently performed an ab initio study of the structural, electronic and magnetic properties of all 3 d transition metal (TM) free-standing atomic chains and found that Fe and Ni nanowires have a giant magnetic anisotropy energy (MAE), indicating that these nanowires would have applications in high density magnetic data storages. In this paper, we perform density functional calculations for the Fe, Co and Ni linear atomic chains on Cu(001) surface within the generalized gradient approximation, in order to investigate how the substrates would affect the magnetic properties of the nanowires. We find that Fe, Co and Ni linear chains on Cu(001) surface still have a stable or metastable ferromagnetic state. When spin–orbit coupling (SOC) is included, the spin magnetic moments remain almost unchanged, due to the weakness of SOC in 3 d TM chains, whilst significant orbital magnetic moments appear and also are direction-dependent. Finally, we find that the MAE for Fe, and Co remains large, i.e., being not much affected by the presence of Cu substrate.

Collectivity atN=40in neutron-richCr64

$^{9}\mathrm{Be}$-induced inelastic scattering of $^{62,64,66}\mathrm{Fe}$ and $^{60,62,64}\mathrm{Cr}$ was performed at intermediate beam energies. Excited states in $^{64}\mathrm{Cr}$ were measured for the first time. Energies and population patterns of excited states in these neutron-rich Fe and Cr nuclei are compared and interpreted in the framework of large-scale shell-model calculations in different model spaces. Evidence for increased collectivity and for distinct structural changes between the neighboring Fe and Cr isotopic chains near $N=40$ is presented.

Magnetic properties of 3d transition metal wires on vicinal Cu(111) surfaces at finite temperature

One-dimensional transition metal (TM) nanowires can be formed on a stepped Cu(111) surface. The basic template is an embedded Fe chain at one-atom distance away from the upper edge of the monoatomic surface step, supplying the deposition of 3d TM chains from V to Co to form on top of the Fe chain. Density functional theory (DFT) is applied to calculate the magnetic properties of these TM-Fe wires. Exchange parameters are extracted from the DFT calculations. A classical Heisenberg model is used in Monte Carlo simulations to study finite temperature effects.

Three New Iron(II) Thiocyanato Coordination Polymers Based on 4,4′‐Bipyridine as Ligand and the Influence of Methanol on Their Structures

AbstractReaction of iron(II) thiocyanate with 4,4‐bipyridine (bipy) in methanol leads to the formation of three new solvates of different composition depending on the reaction conditions: At room temperature two new ligand‐rich 1:2 (1:2 = ratio between metal and N‐donor ligand) polymorphic forms [Fe(NCS)2(bipy)2·2MeOH]n (1I) and [Fe(NCS)2(bipy)(MeOH)2·(bipy)]n (1II) are obtained, whereas solvothermal conditions leads to the formation of the new ligand‐deficient 1:1 compound [{Fe(NCS)2(bipy)(MeOH)}2]n (2). All crystal structures were determined by X‐ray single crystal structure analysis. In the crystal structure of modification 1I the metal atoms are coordinated by four bridging bipy ligands, which connect them into layers. The methanol molecules occupy voids in the structure. Compared to 1I in modification 1II the crystal structure contains of linear Fe–bipy–Fe chains, which are further connected by hydrogen bonds between coordinating MeOH and noncoordinated bipy ligands into layers. The ligand‐deficient 1:1 compound 2 shows a completely different coordination topology with linear Fe–bipy–Fe chains, which are connected by coordinating methanol molecules into double‐chains. In all compounds the thiocyanato anions are terminal N‐bonded to the metal atoms. Investigation of the thermal behavior of compound 1I shows a two‐step decomposition, in which ligand‐deficient intermediates are formed. Magnetic measurements on 1I reveal Curie–Weiss paramagnetism with increasing antiferromagnetic interactions on cooling.

Nuclear magnetic and quadrupole resonances of Cu in the low-dimensional magnets Cu2M2Ge4O13 (M = Fe, Sc)

We report on the results of nuclear magnetic and quadrupole resonances of Cu in Cu2Fe2Ge4O13 consisting of weakly coupled Cu dimers and Fe chains. In the antiferromagnetic state below 39 K, we observed nuclear resonance of Cu under the internal magnetic field at the Cu site. An analysis of the internal field based on the square-planar coordination of Cu2+suggests that the 3d hole is mainly in the dx2−y2 orbital. In Cu2Sc2Ge4O13 including only Cu dimers, we observed oscillation of Cu spin-echo intensity as a function of the separation time between π/2 and π pulses. This is caused by indirect nuclear spin coupling mediated by strong intradimer exchange coupling of the electronic spins, indicating that the dimers are magnetically well isolated in these materials.

Theory of magnetic excitation for coupled spin dimer and spin chain system Cu2Fe2Ge4O13

Cu2Fe2Ge4O13 is a quantum magnet consisting of Cu spin dimers and Fe spin chains. It shows an antiferromagnetic phase transition at low temperatures due to the magnetic moment of Fe. Since the two parts are weakly coupled, magnetic excitations are well separated into high-energy Cu dimer part and low-energy Fe chain part. We study the magnetic excitations in the ordered phase of Cu2Fe2Ge4O13 based on a theory used for coupled spin dimer systems such as TlCuCl3. Analyzing the dynamical spin correlation functions, we find several high-energy modes with longitudinal spin fluctuations peculiar to the coupled spin dimer and spin chain system. This is consistent with the recent experimental result of inelastic neutron scattering. A possibility to detect such longitudinal modes is discussed by means of magnetic Raman scattering.

Structurally driven magnetic state transition of biatomic Fe chains on Ir(001)

Using first-principles calculations, we demonstrate that the magnetic exchange interaction and the magnetocrystalline anisotropy of biatomic Fe chains grown in the trenches of the $(5\ifmmode\times\else\texttimes\fi{}1)$ reconstructed Ir(001) surface depend sensitively on the atomic arrangement of the Fe atoms. Two structural configurations have been considered which are suggested from recent experiments. They differ by the local symmetry and the spacing between the two strands of the biatomic Fe chain. Since both configurations are very close in total energy they may coexist in experiment. We have investigated collinear ferro- and antiferromagnetic solutions as well as a collinear state with two moments in one direction and one in the opposite direction ($\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\uparrow}$-state). For the structure with a small interchain spacing, there is a strong exchange interaction between the strands and the ferromagnetic state is energetically favorable. In the structure with larger spacing, the two strands are magnetically nearly decoupled and exhibit antiferromagnetic order along the chain. In both cases, due to hybridization with the Ir substrate the exchange interaction along the chain axis is relatively small compared to free-standing biatomic iron chains. The easy magnetization axis of the Fe chains also switches with the structural configuration and is out-of-plane for the ferromagnetic chains with small spacing and along the chain axis for the antiferromagnetic chains with large spacing between the two strands. Calculated scanning tunneling microscopy images and spectra suggest the possibility to experimentally distinguish between the two structural and magnetic configurations.

덩어리, 단층 및 사슬 구조 철의 전자구조와 자성에 대한 LDA+U 효과

상관효과 U가 전자구조와 자성에 미치는 영향을 검토하기 위하여 대표적 자성물질인 철의 덩어리, 단층 및 사슬 구조에 대해 연구하였다. 이를 위하여 U = 3 eV로 택하여, 총 퍼텐셜 보강 평면파동 에너지 띠 방법을 이용하여 LDA+U 및 GGA+U 근사 하에 전자구조 계산을 수행하였다. 비교를 위하여 LDA 및 GGA를 이용한 계산도 수행하였다. 그 결과 U의 효과를 포함시켰을 때 덩어리 철의 경우 자기모멘트가 <TEX>$0.3{\mu}_B$</TEX> 증가하여 실험값이나 LDA 및 GGA 계산에 비해 과다하게 계산되는 것으로 나타났으나, 단층이나 사슬의 경우는 그렇게 큰 차이를 보이지 않았다. 이로부터 전자구조 계산 시대상 계에 따라 U의 효과를 적절히 고려하여야 함을 알았다. We examine the effect of U term (U = 3 eV) describing the Coulomb interactions between electrons on the results of electronic band structure calculations carried out for bcc Fe bulk, monolayer, and chain. We investigated the properties of the three Fe structures by using the all-electron total-energy full-potential linearized augmented plane wave method. The U term was included in the exchange - correlation functionals constructed on the basis of local density approximation (LDA) and general gradient approximation (GGA). We found that in the case of bcc Fe bulk structure inclusion of the U term leads to the overestimated values of magnetic moment on Fe atom. The values of magnetic moment calculated for Fe in monolayer and chain are in accordance with calculations in which the U term was not included. In general, for each system the calculated values of magnetic moment on Fe sites were larger when the U term was incorporated in the energy functional. In Fe bulk, the value of magnetic moment <TEX>$2.54{\mu}_B$</TEX> for LDA+U larger than <TEX>$2.25{\mu}_B$</TEX> for LDA.