Two-dimensional Iron Research Articles

Exploring the 2D to 3D dimensionality crossover in thin iron films

The temperature dependence of the spontaneous magnetization of epitaxial iron films with a thickness ranging from d = 2 0 to 200 nm has been measured. The films are grown on GaAs (1 0 0) substrates which are covered by a 150 nm thick silver (1 0 0) buffer layer. For three-dimensional BCC iron it was observed already in 1929 that saturation of the spontaneous magnetization for T → 0 is perfectly described by a T 2 power law. On the other hand, for thin two-dimensional (2D) iron films a T 3/2 law has been established in many recent experimental investigations. In our iron films grown on diamagnetic silver, this dimensionality change occurs at a thickness between d = 1 0 0 and 200 nm. Comparison of the here-observed T 3/2 coefficients with those on iron films grown on paramagnetic tungsten (1 1 0) shows that the 2D interactions are ∼20 times larger in the films on tungsten. Recent results on Fe films which are grown directly on GaAs (1 0 0) confirm that the substrate has a very strong effect on the coefficient of the T 3/2 function, i.e. on the strength of the magnetic interactions in the films.

Growth of carbon nanotubes on a gold (111) surface using two-dimensional iron oxide nano-particle catalysts derived from iron storage protein.

We report here the preparation of two-dimensional iron oxide nano-particles from the iron storage protein ferritin immobilized on a gold surface. This paper also reports the novel finding of the lattice-oriented like growth of carbon nanotubes on a gold (111) surface using the obtained two-dimensional iron oxide nano-particles on the gold surface as a catalyst.

Synthesis, structure, and Mössbauer study of [Fe(H2O)(2)(C(9)O(6)H4)].H2O: a two-dimensional iron(II) trimellitate (MIL-67).

The two-dimensional (2D) iron trimellitate [Fe(H(2)O)(2)(C(9)O(6)H(4))].H(2)O, labeled MIL-67, has been obtained under hydrothermal conditions (473 K, 48 h). In the 2D structure of MIL-67, the Fe(2+) ions display two different octahedral environments: [FeO(4)(H(2)O)(2)] and [FeO(2)(H(2)O)(4)]. These octahedra share an apical water molecule to form infinite chains. The chains are linked by partly deprotonated C(9)O(6)H(4)(2-) anions to give hybrid organic-inorganic layers; the remaining acidic-CO(2)H group is dangling in the interlayer space. Below 8(1) K, MIL-67 displays a canted antiferromagnetic behavior, according to analyses via magnetic measurements and Mössbauer spectroscopy. Crystal data for MIL-67 are as follows: triclinic; space group P1 (No. 2), with a = 6.9671(2) A, b = 7.3089(3) A, c = 12.5097(3) A, alpha = 78.758(1) degrees, beta = 89.542(2) degrees, and gamma = 65.197(1) degrees; volume V = 565.21(3) A(3); and Z = 2.

Insertion of a Two‐Dimensional Iron‐Chloride Network Between Perovskite Blocks. Synthesis and Characterization of the Layered Oxyhalide, (FeCl)LaNb2O7.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Comparison of one-, two-, and three-dimensional iron phosphates containing ethylenediamine

A new two-dimensional (2d) iron phosphate, (C 2N 2H 10)Fe 2O(PO 4) 2, has been synthesized under hydrothermal conditions in the system of FeCl 3–H 3PO 4–C 2N 2H 8–H 2O. The crystal data is: space group P2 1/ c, a=10.670(1) Å, b=10.897(1) Å, c=9.918(1) Å, β=105.632(1)°, Z=4. The layered structure consists of double sheet layers, of composition Fe 2O(PO 4) 2, built from FeO 5 trigonal bipyramids and PO 4 tetrahedra. The amine holds the layers together via H-bonding. The study of the magnetic properties reveals two magnetic transitions at 160 and 30 K with spin-glass-like behavior below 160 K. By varying the hydrothermal conditions, three other iron phosphates were synthesized: the one-dimensional (1d) (C 2N 2H 10)Fe(HPO 4) 2(OH)·H 2O, the 2d (C 2N 2H 10)Fe 2(PO 4) 2(OH) 2, and the three-dimensional (3d) (C 2N 2H 10) 2Fe 4O(PO 4) 4·H 2O. The 1d compound can be used as the starting reagent in the synthesis of both the 2d compound and the 3d lipscombite Fe 3(PO 4) 2(OH) 2 due to the similar building blocks in their structures. In the 3d phosphate (C 2N 2H 10) 2Fe 4O(PO 4) 4·H 2O, manganese can substitute for half of the iron atoms. Magnetic study shows ordering transitions at about 30 K, however, manganese substitution depresses the magnetic ordering temperature.

Monolayer, bilayer, multilayers: evolving magnetic behavior in Langmuir-Blodgett films containing a two-dimensional iron-nickel cyanide square grid network.

The assembly of two-dimensional cyanide-bridged Fe(III)-Ni(II) square grid networks at the air-water interface and subsequent transfer of these networks as isolated monolayer, isolated bilayer, and multiple bilayer (multilayer) films via the Langmuir-Blodgett technique results in novel low-dimensional systems in which the effects of dimensionality on magnetic behavior in molecule-based materials can be observed. The magnetic response of these films between 2 < T < 300 K in dc fields from -50 < H < 50 kG and in 4 G ac fields from 1 Hz to 1 kHz are reported. The results show the presence of ferromagnetic domains with characteristic hysteresis in each of the three systems. The magnetic response for all three samples is anisotropic with a stronger field-cooled magnetization observed when the planes of the films are aligned parallel to the applied field. Additionally, each of the three samples shows frequency dependence in both the real and imaginary components of the ac susceptibility. This behavior is interpreted as being characteristic of spin glass-type ordering of ferromagnetic domains to form a cluster glass. A lower glass temperature (T(g)) is observed in the isolated monolayer film relative to the bilayer and multilayer samples. The bilayer sample shows two glass transitions at T(g1) = 3.8 K and T(g2) = 5.4 K, whereas only one transition at T(g) = 5.4 K is observed in the multilayer sample. The different magnetic responses of the three films are attributed to different in-plane, interplane, and long-range dipolar exchange interactions.

Insertion of a Two-Dimensional Iron-Chloride Network between Perovskite Blocks. Synthesis and Characterization of the Layered Oxyhalide, (FeCl)LaNb2O7

A low-temperature (350 °C) ion-exchange reaction was used to insert Fe−Cl layers between the perovskite blocks of a double-layered Dion−Jacobson compound. The product, (FeCl)LaNb2O7, contains iron coordinated by two apical oxygens from the perovskite layer and four in-plane chlorines within the interlayer space. Rietveld structural analysis of X-ray powder diffraction data confirms the formation of the two-dimensional iron−chlorine networks with the iron cations moving slightly off the ideal octahedral coordination. Thermal analyses in oxygen, argon, and hydrogen showed this compound is metastable, decomposing exothermically between 600 and 750 °C. Magnetic measurements show Curie−Weiss behavior at higher temperatures consistent with Fe2+ in a high-spin d6 configuration. At lower temperatures two transitions are observed: below 80 K an antiferromagnetic transition occurs, and below 10 K spins realign in a ferromagnetic fashion.

Synthesis and Characterization of a New Ferrimagnetic Mixed‐Valent Iron Fluorophosphate [C6N4H21] [FeIII3‐xFeIIxF2 (PO4)(HPO4)2]2 (x ≈ 1.5) with a Layered Structure.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Oxalate and 2,2′-bipyrimidine as bis-chelating ligands in the honeycomb layered compound {[Fe2(bpym)(ox)2]·5H2O}n

The novel two-dimensional iron(II) compound of formula {[Fe2(bpym)(ox)2]·5H2O}n (1) [bpym = 2,2′-bipyrimidine and ox = oxalate dianion] is obtained by reaction of oxalic acid, iron(II) chloride and 2,2′-bipyrimidine in aqueous solution. The structure of 1 is made up of oxalato-bridged iron(II) chains cross-linked by bischelating bpym affording a honeycomb lattice. Variable-temperature magnetic susceptibility data of 1 show the occurrence of relatively large antiferromagnetic interactions between the high spin iron(II) ions separated by more than 5.5 Å through bridging bpym [Jbpym = −4.0(2) cm−1] and ox [Jox = ca. −7.8(2) cm−1] ligands. These values compare well with those obtained in the iron(II) chain [Fe(dpa)(ox)]n (2) [Jox = −8.0(2) cm−1] (dpa = 2,2′-dipyridylamine) and dinuclear {[Fe(H2O)4]2(bpym)}(SO4)2·2H2O (3) (Jbpym = −3.4 cm−1) compounds where bischelating ox (1 and 2) and bpym (1 and 3) groups and the bidentate dpa (2) ligand are present.

Temperature dependence of the spontaneous magnetization of body-centred-cubicbulk iron, amorphous iron and thin iron films

It is shown that the thermal decrease of the spontaneous magnetization ofiron differs characteristically depending on the preparation conditions.In all cases, the deviations from saturation at absolute zero can beaccurately described by a single temperature power term Tε whichholds up to several hundreds of kelvins. The empirical exponents are ε = 2 for crystalline bulkiron, ε = 3/2for amorphous iron as well as for isotropic (crystalline) two-dimensional iron films, butε = 5/2for inhomogeneous (pseudomorphic) monatomic layers. In crystalline films which aresufficiently thick (∼100–300 nm) to allow the excitation of standing spin waves, theT2bulk law is confirmed for the uniform precession mode, but for states with aperiodically modulated magnetization due to spin wave resonance, a T3/2dependence holds. For ultrathin iron films with more thanthree atomic layers, a thermodynamic crossover from T3/2 toT2 isobserved at higher temperatures. This is indicative of a dimensionality change of therelevant interactions from 2 to 3. Crystalline and amorphous bulk iron also exhibit acrossover, but only for the amplitude and not for the exponent of the Tε law.This is assumed to be caused by the thermal variation of the magneticinteraction strength. All observed empirical exponents ε fitinto a recently proposed scheme of universality classes for the low-temperaturebehaviour of the order parameter in materials with half-integer spin quantum numberand three-, two-and one-dimensional interactions. It can therefore be concludedthat the thermodynamics of iron is like that of an insulating material withs = 1/2.

Synthesis and Characterization of a New Ferrimagnetic Mixed-Valent Iron Fluorophosphate [C6N4H21][FeIII3-xFeIIxF2(PO4)(HPO4)2]2 (x ∼ 1.5) with a Layered Structure

The synthesis, structure, and magnetic properties of a mixed valent iron fluorophosphate, [C6N4H21][FeIII3-xFeIIxF2(PO4)(HPO4)2]2 (x ∼ 1.5) has been described. The structure consists of a network of FeO4F2 octahedra and PO4 tetrahedra linked through their vertexes, forming infinite two-dimensional sheets separated by the organic amine molecules, triethylenetetrammonium cations (TETA). A remarkable feature of this structure is the presence of chains of FeII−O−FeII that are connected by FeIII octahedra, forming infinite two-dimensional sheets of Fe−O/F−Fe. This is the first time such linkages have been observed in two-dimensional iron fluorophosphates. Magnetic studies indicate ferrimagnetic behavior with a Curie temperature of Tc = 25 K. Mössbauer studies show mixed occupancies in the FeII sites. Crystal data: M = 567.61, triclinic, space group = P1̄ (no. 2), a = 6.431(4) Å, b = 10.274(5) Å, c = 10.439(3) Å, α = 80.56(4)°, β = 89.53(2)°, γ = 87.94(4)°, V = 680.0(6) Å3, Z = 2, ρ(calc.) = 2.772 g cm-3, μ(Mo Kα) = 3.610 mm-1, R1 = 0.0634 [1943 observed reflections with I > 2σ(I)].

Solid-state Water-mediated Transport Reduction of Nanostructured Iron Oxides

The Fe2+/Fe3+ ratio in two-dimensional iron oxide nanosructures (nanolayers with a thickness of 0.3–1.5 nm on silica surface) may be precisely controlled using the transport reduction (TR) technique. The species ≡–O–Fe(OH)2 and (≡Si–O–)2–FeOH forming the surface monolayer are not reduced at 400–600°C because of their covalent bonding to the silica surface, as demonstrated by Mossbauer spectroscopy. Iron oxide microparticles (microstructures) obtained by the impregnation technique, being chemically unbound to silica, are subjected to reduction at T ≥ 500°C with formation of metallic iron in the form of α-Fe. Transport reduction of supported nanostructures (consisting of 1 or 4 monolayers) at T ≥ 600°C produces bulk iron(II) silicate and metallic iron phases. The structural-chemical transformations occurring in transport reduction of supported iron oxide nanolayers are proved to be governed by specific phase processes in the nanostructures themselves.

One-Dimensional Iron(III) and Two-Dimensional Iron(III)Nickel(II) Cyanide-Bridged Ferromagnetic Arrays from Hexacyanoferrate(III) and [Ni(cyclam)]2± Building Blocks: Synthesis, Crystal Structure and Magnetic Properties

The X-ray structures and magnetic properties of a iron(III) linear chain and a honeycomb-like layered iron(III)-nickel(II) cyanide-bridged compound are reported. The former contains alternating iron sites and unexpected ferromagnetic behaviour, justified on the basis of the axial distortion from regular octahedral geometry of one of the iron ions. The latter is metamagnetic with ferromagnetic intralayers and antiferromagnetic interlayers interactions with a Néel temperature, TN= 7.7 K. The field-induced transition from an antiferro- to a ferromagnetic state takes place at Hc= 5000 G. The antiferromagnetic ordered phase exhibits spin-canting and long range ferromagnetic ordering at 3 K with a characteristic hysteresis loop.

A Two-Dimensional Iron Phosphate Templated by Ethylenediamine

[Fe(PO 4 )(OH)].0.5(ethylenediamine) was synthesized hydrothermally at 453 K. It is isotypic with the layered gallophosphate obtained in ethylene glycol by Jones, Thomas, Qisheng, Hursthouse & Chen [J. Chem. Soc. Chem. Commun. (1991), pp. 1520-1522].

The Structure of Transition Metal Graphite Compounds: Iron- and Ruthenium-Graphite

Abstract The so called iron- and ruthenium-graphite compounds prepared by the reduction of stage-1 FeCl3-GIC and stage-2 RuCl3-GIC with hydrogen and K-naphthalenide/THF solutions were investigated by XRD, SEM with EDX and TEM. The structural properties of these compounds are discussed with regard to possibly exisisting two-dimensional iron- and ruthenium-graphite.