Fe Chains Research Articles

Magnetic properties of 3d transition metal chains on vicinal [formula omitted] surface

Density functional theory (DFT) is applied in our study to describe magnetic properties of 3d transition metal (TM) nanowires on a stepped Cu ( 1 1 1 ) surface. The basic template to study such metallic chains on the Cu ( 1 1 1 ) surface is an embedded Fe chain at one-atom distance away from the upper edge of the monoatomic surface step. Chains of 3d transition metal atoms from Sc to Ni are added on top of the Fe chain. At the beginning of the 3d row, the chains show antiferromagnetic order. A small energy difference between ferromagnetic and antiferromagnetic order is obtained for the Mn–Fe system. Cr forms an antiferromagnetic chain, whereas Fe, Co, and Ni chains are ferromagnetically coupled to the embedded Fe chain.

Connection between magnetism and structure in Fe double chains on the Ir(100) surface

The magnetic ground state of nanosized systems such as Fe double chains, chains recently shown to form in the early stages of Fe deposition on Ir(100), is generally nontrivial. Using ab initio density functional theory we find that the straight ferromagnetic (FM) state typical of bulk Fe as well as of isolated Fe chains and double chains is disfavored after deposition on Ir(100) for all the experimentally relevant double chain structures considered. So long as spin-orbit coupling (SOC) is neglected, the double chain lowest energy state is generally antiferromagnetic (AFM), a state which appears to prevail over the FM state due to Fe-Ir hybridization. Successive inclusion of SOC adds two further elements, namely, a magnetocrystalline anisotropy and a Dzyaloshinskii-Moriya (DM) spin-spin interaction; the former stabilizing the collinear AFM state and the latter favoring a long-period spin modulation. We find that anisotropy is most important when the double chain is adsorbed on the partially deconstructed Ir(100)---a state which we find to be substantially lower in energy than any reconstructed structure---so that in this case the Fe double chain should remain collinear AFM. Alternatively, when the same Fe double chain is adsorbed in a metastable state onto the $(5\ifmmode\times\else\texttimes\fi{}1)$ fully reconstructed Ir(100) surface, the FM-AFM energy difference is very much reduced and the DM interaction is expected to prevail, probably yielding a helical spin structure.

Electronic structure and magnetic anisotropy of a constrained Fe chain in an electricfield

The electronic structure and magnetic anisotropy were studied for a constrained iron chain inan electric field by means of the first-principles approach. The electron induced by the electricfield was found to occupy mainly the extended s-like orbitals which is well hybridized with thed3z2−r2 localized orbital. The magnetic anisotropy was observed to decrease with thenumber of induced electrons and to depend on the magnetization direction. Themagnetization perpendicular both to the chain and the electric field modifies theelectron dispersion relation to be asymmetrical, which implies an expectation ofvariable transport property with both the external electric and magnetic fields.

Uniaxial magnetic anisotropy of quasi-one-dimensional Fe chains on Pb∕Si

We fabricated quasi-one-dimensional Fe chains on a 4° miscut Si (111) substrate with a Pb film as a buffer layer. The magnetic properties and morphology of Fe chains were investigated by means of scanning tunneling microscope (STM) and surface magneto-optical Kerr effect (SMOKE). STM images show that Fe chains are formed by Fe random islands along the steps of the Pb film due to step decoration. SMOKE data indicate that the Fe chains exhibit in-plane uniaxial magnetic anisotropy along the step direction. The effective in-plane uniaxial anisotropy constant at room temperature was determined by means of electron spin resonance.

Ligand-directed assembly of cyanide-bridged bimetallic MnIIFeIIIcoordination polymers based on the pentacyanoferrite(III) building blocks

Rarely investigated pentacyanoferrate(III) building blocks, [Fe(CN)5(L)]2− (L = 1-methylimdazole (1–CH3im), imidazole (imH)), have been used to prepare cyanide-bridged bimetallic polymeric Mn(II)–Fe(III) complexes {[Mn(bpy)(H2O)2Fe(CN)5(1–CH3im)]·H2O}n (1), {[Mn(bpy)Fe(CN)5(imH)]·H2O}n (2) and {[Mn(CH3OH)2Fe(CN)5(imH)]}n (3) (bpy = 2,2′-bipyridine). Complexes 1 and 2 were obtained via the reactions of Mn(bpy)2Cl2·EtOH with [Fe(CN)5(L)]2− (L = 1–CH3im and imH, respectively), and complex 3via the reaction between MnCl2·2H2O and [Fe(CN)5(imH)]2− in absolute methanol. Complex 1 is a one-dimensional alternate Mn(II)–Fe(III) chain, while complexes 2 and 3 are two-dimensional comprised of Fe2Mn2 squares. Complexes 2 and 3 show interesting intra- or interlayer π–π interactions between imidazole and pyridine rings of bpy. Partial loss of the bpy ligand and the π–π contacts has a direct effect on the molecular structures of complexes 1–3. Antiferromagnetic interaction between high-spin Mn(II), and low-spin Fe(III) has been observed in complexes 1–3, and the layered complexes 2 and 3 display long-range magnetic ordering at the critical temperature of 4.4 K (TN) for 2 and 5.0 K (Tc) for 3. A best-fit to the magnetic susceptibility of the 1D complex 1 has given the magnetic coupling constant of JMnFe = −6.16(9) cm−1 based on an antiferromagnetic chain model of alternate SFe = 1/2 and SMn = 5/2 spins.

Anisotropic superexchange in one-dimensional Fe-chains on InAs(1 1 0)

The magnetic and electronic properties of Fe chains on InAs(1 1 0) are calculated from first-principles using the density functional theory. The magnetic ground state is found to be antiferromagnetic (AF) for Fe chains along [1 −1 0] direction and ferromagnetic (FM) for Fe chains along the perpendicular [0 0 1] direction. The AF structure is explained with an AF superexchange between Fe atoms via mediating As, while the FM structure is explained with a more complicated exchange path via surface As and In atoms.

Magnetic anisotropy ofFe∕Pt(001)andPt∕Fe∕Pt(001)using a first-principles approach

We investigated the magnetic anisotropy of an iron layer on a Pt(001) surface and some related systems by employing the local spin density approximation in a theoretical ab initio approach. We found that the surface system $\mathrm{Pt}∕\mathrm{Fe}∕\mathrm{Pt}(001)$ showed a perpendicular magnetic anisotropy and its anisotropy energy per iron atom amounted to a value which is 2 times larger than the value of bulk FePt. The surface relaxation much enhances the anisotropy energies, related to a large attractive force between the iron and platinum layers. A remarkable cap effect---that the covering platinum layer changes anisotropy energy---was also found to exist. We investigated the microscopic origin of the perpendicular anisotropy in relation to the local densities of states of the Fe atom. These quantities were discussed as a fingerprint of magnetic anisotropy in comparison with the results of the Fe chain at the step edge on a vicinal surface Pt(664). The atomic orbital magnetic moments were enhanced at the respective surface atoms.

Single-chain magnets constructed with a twisting arrangement of the easy-plane of iron(II) ions

Abstract A novel class of single-chain magnets (SCMs), catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4 and its derivative, were synthesized using the spin-carrier components possessing hard-axis anisotropy (or easy-plane anisotropy, D > 0). The easy-axis-type anisotropy of whole molecules of these compounds, which is essential for the formation of SCMs, arises from the twisted arrangement of easy-planes of Fe(II) along the chain axis. Alternating high-spin Fe(II) and low-spin Fe(III) chain complexes behave as an SCM with a typical frequency-dependent ac susceptibility which obeys Arrhenius law. Below 7 K, catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4 showed a short-range spin-ordering even in zero external field in a time range of Mössbauer spectroscopy as well as the muon-spin-relaxation (μSR) spectroscopy. Since the easy-axis-type magnetic anisotropy originated from the structural motif of the twisting arrangement of Fe(II) ions, the overall magnetic property was very sensitive to the small structural changes arising from adsorption/desorption of the crystal solvents, and catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4 showed a reversible change in magnetism that has been referred to as "a magnetic sponge". In its derivative, controls of the molecular structure, the arrangement of chains in the crystal, and magnetic properties both in dc and ac susceptibility have been achieved by the introduction of methyl group on a bpca- ligand, which bridges and mediates the magnetic interaction of the adjoining Fe(II)/Fe(III) ions.

1D and 2D FeII Azide Coordination Polymers with Ferromagnetic Canting

AbstractThe two compounds [FeII(pyridine)2(N3)2(H2O)] (1) and [FeII(4‐acetylpyridine)2(N3)2] (2) were prepared. The X‐ray crystal structures show end‐to‐end (EE) bridging azides in both cases with a 1D Fe–NNN–Fe chain for 1 and a 2D Fe–NNN–Fe net in 2. Both compounds show similar magnetic behaviour where the high‐temperature data are consistent with antiferromagnetic couplings and the low‐temperature data indicate ferrimagnetic ordering based on spin canting at 20 and 45 K. Compound 2 also shows a hysteresis loop. These findings are compared to the related 3D coordination polymer [Fe(N3)2(4,4′‐bipyridine)]. According to network analyses the latter compound was shown to contain the new uninodal six‐connected‐network topology (510 · 64 · 7)‐jsm. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Systematicab initiostudy of the magnetic and electronic properties of all3dtransition metal linear and zigzag nanowires

The magnetic and electronic properties of both linear and zigzag atomic chains of all $3d$ transition metals have been calculated within density functional theory with the generalized gradient approximation. The underlying atomic structures were determined theoretically. It is found that all the zigzag chains except the nonmagnetic Ni and antiferromagnetic (AF) Fe chains, which form a twisted two-legger ladder, look like a corner-sharing triangle ribbon and have a lower total energy than the corresponding linear chains. All the $3d$ transition metals in both linear and zigzag structures have a stable or metastable ferromagnetic (FM) state. Furthermore, in the V, Cr, Mn, Fe, and Co linear chains and Cr, Mn, Fe, Co, and Ni zigzag chains, a stable or metastable AF state also exists. In the Sc, Ti, Fe, Co, and Ni linear structures, the FM state is the ground state, while in the V, Cr, and Mn linear chains, the AF state is the ground state. The electronic spin polarization at the Fermi level in the FM Sc, V, Mn, Fe, Co, and Ni linear chains is close to 90% or above, suggesting that these nanostructures may have applications in spin-transport devices. Interestingly, the V, Cr, Mn, and Fe linear chains show a giant magnetolattice expansion of up to 54%. In the zigzag structure, the AF state is more stable than the FM state only in the Cr chain. Both the electronic magnetocrystalline anisotropy and magnetic dipolar (shape) anisotropy energies are calculated. It is found that the shape anisotropy energy may be comparable to the electronic one and always prefers the axial magnetization in both the linear and zigzag structures. In the zigzag chains, there is also a pronounced shape anisotropy in the plane perpendicular to the chain axis. Nonetheless, in the FM Ti, Mn, and Co linear chains and AF Cr, Mn, and Fe linear chains, the electronic anisotropy is perpendicular, and it is so large in the FM Ti and Co linear chains as well as in AF Cr, Mn, and Fe linear chains that the easy magnetization axis is perpendicular. In the AF Cr and FM Ni zigzag structures, the easy magnetization direction is also perpendicular to the chain axis, but in the ribbon plane. Remarkably, the axial magnetic anisotropy in the FM Ni linear chain is gigantic, being $\ensuremath{\sim}12\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$/atom, suggesting that Ni nanowires may have applications in ultrahigh density magnetic memories and hard disks. Interestingly, there is a spin-reorientation transition in the FM Fe and Co linear chains when the chains are compressed or elongated. Large orbital magnetic moment is found in the FM Fe, Co, and Ni linear chains. Finally, the band structure and density of states of the nanowires have also been calculated to identify the electronic origin of the magnetocrystalline anisotropy and orbital magnetic moment.

Magnetic anisotropies of iron on the Pt(111) surface

We have studied magnetic anisotropies of Fe atoms on the platinum (111) surface,employing a fully relativistic pseudopotential and plane wave method with the local spindensity approximation. We investigated three surface structures with different Femonolayer coverages: full coverage, half-coverage and quarter-coverage. The effect of surfacerelaxation has been included. It was found that the magnetic easy axis of the system iswithin the surface plane for all systems investigated. In the system of an Fe chain onPt(111), having an anisotropic local structure, the magnetic anisotropy energy is muchenhanced after surface relaxation. This absolute value is larger compared with the value forbulk alloy and the magnetic easy axis is directed parallel to the alignment of Featoms.

Bonding differences between single iron atoms versus iron chains with carbon nanotubes: First-principles calculations

We have studied the adsorption of both single Fe atoms and Fe chains in carbon nanotubes by the first-principles methods. We find that a single Fe atom bonds stably with carbon nanotubes, while Fe chains do not bond stably with carbon nanotubes except for the small size nanotubes. The configurations for the $d$ electrons in the single Fe atoms and in the Fe chains are very different. We propose a physical mechanism and show that the transfer energy of spin-up electrons in a half-filled $d$ orbital to the spin-down electrons in another half-filled $d$ orbital determines the bonding ability of single Fe atoms and Fe chains with carbon nanotubes. The results explain the experiment that Fe nanowires are easy to move inside the nanotubes.

Indirect magnetic interaction mediated by a spin dimer inCu2Fe2Ge4O13

${\mathrm{Cu}}_{2}{\mathrm{Fe}}_{2}{\mathrm{Ge}}_{4}{\mathrm{O}}_{13}$ is a bicomponent compound that consists of Cu dimers and Fe chains with separate energy scale. By inelastic neutron scattering technique with high-energy resolution we observed the indirect Fe-Fe exchange coupling by way of the Cu dimers. The obtained parameters of the effective indirect interaction and related superexchange interactions are consistent with those estimated semistatically. The consistency reveals that the Cu dimers play the role of nonmagnetic media in the indirect magnetic interaction.

Electronic states of Fe atoms and chains on InAs(110) from scanning tunneling spectroscopy

The local density of states (DOS) on and around Fe single atoms and Fe chains deposited on the $n\text{\ensuremath{-}}\mathrm{In}\mathrm{As}(110)$ surface is studied by scanning tunneling spectroscopy at $T\ensuremath{\simeq}6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The single atom shows two characteristic states in the filled as well as in the empty DOS which are attributed to an In-related and an Fe-related state. For chains longer than two atoms oriented along the $[1\overline{1}0]$ direction, the In-related state results in a uniform state, while the Fe-related state splits up into an end state and inner states. The end state has a lower energy in the filled as well as in the empty DOS. Chains oriented along the [001] direction show an electronic structure which varies continuously along their axis, suggesting a position-dependent hybridization of each atom to the substrate.

Magnetic order and exchange interactions in monoatomic3dtransition-metal chains

Based on first-principles calculations we analyze the magnetic order and the exchange interactions in monoatomic $3d$ transition-metal chains of V, Cr, Mn, Fe, and Co. While freestanding Fe and Co chains remain ferromagnetic in the entire range of interatomic distances, V, Cr, and Mn chains change their magnetic state from antiferromagnetic (AFM) to ferromagnetic (FM) upon stretching. The corresponding distance-dependent exchange interaction is in striking resemblance to the Bethe-Slater curve. We demonstrate that in combination with the symmetry reduction on the $(110)$ surfaces of Cu, Pd, Ag, and $\mathrm{NiAl}$ even a weak chain-surface hybridization is sufficient to dramatically change the magnetic coupling in the chains. In particular, we find a tendency towards antiferromagnetic coupling. The obtained magnetic state of a specific chain depends sensitively on the chemical composition and the lattice constant of the surface. Surprisingly, Cr and Mn chains show a transition from ferromagnetic coupling in freestanding chains to antiferromagnetic coupling on the (110) surfaces of Pd, Ag, and $\mathrm{NiAl}$. For Fe and Co chains on $\mathrm{NiAl}(110)$ the FM and AFM states differ by only $2\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, suggesting the possibility of a more complex, noncollinear magnetic ground state.

나노 구조 철띠의 자성과 전자구조에 대한 제일원리 연구

나노 구조 철띠의 자기적 성질을 일반기울기 근사(GGA)를 채택한 전전자 full-potenial linearized augmented plane-wave(FLAPW)에너지 띠 방법을 이용하여 이론적으로 연구하였다. 세 줄, 다섯 줄, 일곱 줄의 철선으로 이루어진 띠에서 가장자리 줄의 자기모멘트는 2.97 또는 2.98 <TEX>${\mu}_B$</TEX>로 Fe 단일 직선의 값과 비슷하게 포화된 값을 가졌으며, 가운데 선의 자기모멘트는 2.82 <TEX>${\mu}_B$</TEX>로 2차원 격자의 값과 같았다. 일곱 줄로 이루어진 철 띠의 전하밀도나 스핀밀도는 가장자리 영역에서 거의 평평한 분포를 보였는데, 이는 가장자리 원자로부터 배출된 p-전자로 인한 가리기에 의한 것이다. 일곱 줄로 이루어진 철 띠에서 가장자리 원자의 상태밀도는 가운데 원자에 비해 띠폭이 줄어들었는데 이는 가장자리 효과에 의한 띠좁힘 때문이다. We investigated the magnetic properties of Fe nanostripes by using the all electron full-potenial linearized augmented plane-wave (FLAPW) energy band method within the generalized gradient approximation (GGA). The magnetic moments of the Fe atoms in the edge Fe chains of the stripes composed of three, five, and seven chains have saturated values of 2.97 or 2.98 <TEX>${\mu}_B$</TEX>, and the values of the center chains are 2.82 <TEX>${\mu}_B$</TEX> which is similar to that of 2D square lattice. The charge and spin density contour plots showed that the flat distribution in the edge region of the stripes, and it is due to the spilled out p-electrons from the atoms in the edge line. The calculated density of states for the edge atoms in the stripes with seven Fe chains showed that the narrowed width compared to that of center atoms due to the band narrowing effect at the edge.

C–Fe chains due to segregated carbon impurities on Fe(1 0 0)

Bulk carbon impurities segregate at the Fe(1 0 0) surface and, upon thermal annealing, can form metastable surface phases with local and long range order and peculiar electronic properties. We present a surface science study of C–segregated Fe(1 0 0) with scanning tunneling microscopy, angle resolved photoemission, and ab initio calculations of the surface structure and electron states. In particular the c(3√2 × √2) structure, observed for 0.67 atomic layers of C segregated at the iron surface, is found to be due to self-organized carbon stripes made of zig-zag chains. The strong hybridization between C and Fe was observed in ARPES spectra.

Electronic, optical, and magnetic properties of Fe-intercalatedH2Ti3O7nanotubes: First-principles calculations and experiments

The electronic structures and optical properties of titanate nanotubes have been studied. It was shown that H2Ti3O7 is a large gap insulator with an energy gap of 3.3 eV, and Fe intercalation into the interlayer region of the layered H2Ti3O7 structure greatly reduces the band gap and improves significantly the visible light absorbtion property of this material. Detailed first-principle calculations revealed that a stable structure exists for the Fe-intercalated H2Ti3O7 structure with a formula FeHTi6O14. The intercalated Fe atoms in the interlayer region of FeHTi6O14 form a one-dimensional (1D) Fe chain along [010], and the overlapped Fe-3d(z)(2) orbitals along the channel result in a delocalized 1D band below the Fermi level extending the absorption edge of FeHTi6O14 well into the visible region. This 1D Fe chain also results in a large exchange splitting between the majority and minority spins, making FeHTi6O14 a promising magnetic insulator with interesting magnetic properties.

1D Lattice Distortions as the Origin of the(2×2)p4gmReconstruction inγ′−Fe4N(100): A Magnetism-Induced Surface Reconstruction

The (100) surface of magnetic gamma'-Fe4N films epitaxially grown on Cu(100) shows a (2 x 2)p4gm reconstruction. The atom positions determined experimentally are properly accounted for by first-principles total energy calculations, which further reveal that the (2 x 2)p4gm reconstruction requires the topmost Fe4N2 plane to be magnetic and effectively decoupled from the rest of the crystal and that it originates from the perpendicular crossing of one-dimensionally dimerized Fe chains.

Ag(001) 표면 위에 놓인 Fe 선의 자성과 전자구조

The electronic structure and magnetism of Fe chain along the [110] direction on Ag(001) were investigated by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within generalized gradient approximation (GGA). The magnetic moment of Fe atom in Fe chain is calculated to be , which is slightly larger than that () of the Fe[110] chain on Cu(001). The reduced coordination number for the Fe chain induced the Fe-d band narrowing and exchange-splitting enhancement, which are responsible for the large magnetic moment of the Fe chain. The calculated band width of the Fe-d band and the exchange-splitting are 1.7 eV and 3.2 eV, respectively.