Fe Intercalation Research Articles

The moderate electron-spin interaction in Fe-intercalated NbSe2

Abstract The interaction between charge and spin degrees of freedom has always been the central issue of condensed matter physics, and transition metal dichalcogenides (TMDs) provide an ideal platform to study it benefiting from their highly tunable properties. In this article, the influence of Fe intercalation in NbSe2 was elaborately investigated using a combination of techniques. Magnetic studies have shown that the insertion of Fe atoms induces an antiferromagnetic state in which the easy axis aligned out of the plane. The sign reversal of the magnetoresistance across the Neel temperature can be satisfactorily explained by the moderate interaction between electrons and local spins. The Hall and Seebeck measurements reveal a multi-band nature, and the contribution of various phonon scattering processes is discussed based on the thermal conductivity and specific heat data.

High-temperature Néel skyrmions in Fe3GaTe2 stabilized by Fe intercalation into the van der Waals gap

Two-dimensional (2D) van der Waals (vdW) magnets that exhibit ferromagnetism at ambient temperature show great promise for spintronic applications. However, until now, only a few pristine or doped 2D magnets have demonstrated the ability to host non-collinear spin textures, thereby limiting their potential applications. Here we directly observe Néel-type skyrmions in the metallic vdW magnetic compound Fe3GaTe2 (FGaT) up to temperatures well above room temperature (≈340 K) in the absence of any external magnetic field. We show that the presence of defects in the structure of FGaT make its structure acentric and therefore compatible with hosting skyrmions that would otherwise not be possible. Indeed, in this regard it is very similar to the closely related compound Fe3GeTe2 (FGT), whose structure with the same space group P3m1 is also realized by defects. Interestingly, however, FGaT accommodates a significantly higher concentration of Fe within the vdW gaps, likely accounting for its enhanced Curie temperature (TC). In addition to the Néel skyrmions observed in the temperature range of 250–340 K, we also detect type-I and -II Bloch-type skyrmionic bubbles in the temperature range of 100–200 K due to an enhanced magnitude of dipole-dipole interactions relative to the Dzyaloshinskii-Moriya exchange interaction. Self-intercalation is thus a highly interesting property of vdW magnets that considerably modifies their fundamental properties.

Fe-Incorporated Metal-Organic Cobalt Hydroxide Toward Efficient Oxygen Evolution Reaction

Metal-organic cobalt hydroxide emerges as a cost-effective electrocatalyst for the oxygen evolution reaction (OER) in energy conversion. However, the limited active sites and poor conductivity hinder their large-scale application. This study employed salicylate as a bridging ligand to synthesize iron-incorporated metal-organic cobalt hydroxide. The influence of Fe intercalation on Co(OH)(Hsal) (where Hsal denotes o-HOC6H4COO−) was investigated using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Fe0.2Co0.8(OH)(Hsal) demonstrates remarkable electrocatalytic activity, displaying an OER overpotential of 298 mV at 10 mA cm−2 and a Tafel slope of 57.46 mV dec−1. This enhancement can be attributed to improved charge transfer kinetics and increased active sites. This work highlights the crucial role of Fe in improving the efficiency of Co-based oxygen-evolving catalysts (OECs) and its potential for boosting efficient hydrogen generation in alkaline environments.Graphical

Tuning Anisotropic Thermoelectric Properties of TiS2–δ Compounds via Intercalating Iron

Layered TiS2 is of great potential in thermoelectrics for room temperature and medium temperature applications due to its tunable transport properties, low environmental impact, low cost, and lightweight. Herein, we prepared FexTiS2–δ with x varying from 0 to 0.05 through a two-step process, involving initial synthesis in sealed tubes followed by spark plasma sintering. Mössbauer spectroscopy indicated that Fe atoms occupy the octahedral sites in the van der Waals gaps and exist in the form of Fe2+ with a high spin state. FexTiS2–δ with x ≤ 0.02 exhibit high in-plane power factors, reaching an average of ~ 1.2 mWm–1K–2. The structural disorder caused by Fe intercalation leads to a significant decrease in out-of-plane lattice thermal conductivity. The anisotropy in the figure of merit, ZT, of FexTiS2–δ is suppressed due to Fe intercalation. Fe0.01TiS2–δ possesses the highest ZT of 0.39 at 625K along the in-plane direction.

Graphitic carbon nitride membranes intercalated with nano-sized Fe-MOF for enhanced water purification via synergistic separation and Fenton-like processes

Versatile two-dimensional nanomaterials have offered a promising prospect to enhance the water purification efficiency and overcome the fouling obstacle in membrane technology. In this work, a graphitic carbon nitride (g-C3N4) nanosheet membrane intercalated with the nano-sized Fe-based metal-organic framework (MIL-100(Fe)) is developed for the enhanced removal of aqueous organic contaminants by synergically promoting separation and Fenton-like processes. The g-C3N4/MIL-100(Fe) membrane is constructed through a self-assembly route in which the nano-MIL-100(Fe) is anchored into g-C3N4 layers by the coordination bonds between Fe nodes and pyridinic N. The MIL-100(Fe) intercalation not only enlarges the interlayer spacing to raise the membrane permeability, but also expedites the electron transfer between Fe2+ and Fe3+ to improve the Fenton-like activity. With a stable water flux of 98.2 L m2·h−1·bar−1 under wide-range pH and pressures, the g-C3N4/MIL-100(Fe) membrane shows high dye removal efficiency (≥99%) and prominent self-cleaning ability. Mechanism insight proposes a combination of size exclusion, electrostatic interaction and steady radical generation. The intercalation of nano-MIL-100(Fe) into g-C3N4 membranes can realize the mutual promotion between separation and Fenton-like processes, the synergistic effect of which provides an effective and feasible strategy for aqueous pollution abatement.

Fe-Intercalation Dominated Ferromagnetism of van der Waals Fe3 GeTe2.

Fe3 GeTe2 have proven to be of greatly intrigue. However, the underlying mechanism behind the varying Curie temperature (Tc ) values remains a puzzle. This study explores the atomic structure of Fe3 GeTe2 crystals exhibiting Tc values of 160, 210, and 230 K. The elemental mapping reveals a Fe-intercalation on the interstitial sites within the van der Waals gap of the high-Tc (210 and 230 K) samples, which are observed to have an exchange bias effect by electrical transport measurements, while Fe intercalation or the bias effect is absent in the low-Tc (160 K) samples. First-principles calculations further suggest that the Fe-intercalation layer may be responsible for the local antiferromagnetic coupling that gives rise to the exchange bias effect, and that the interlayer exchange paths greatly contribute to the enhancement of Tc . This discovery of the Fe-intercalation layer elucidates the mechanism behind the hidden antiferromagnetic ordering that underlies the enhancement of Tc in Fe3 GeTe2 .

Fe(III) Docking-Activated Sites in Layered Birnessite for Efficient Water Oxidation

Non-noble metal catalysts for promoting the sluggish kinetics of oxygen evolution reaction (OER) are essential to efficient water splitting for sustainable hydrogen production. Birnessite has a local atomic structure similar to that of an oxygen-evolving complex in photosystem II, while the catalytic activity of birnessite is far from satisfactory. Herein, we report a novel Fe-Birnessite (Fe-Bir) catalyst obtained by controlled Fe(III) intercalation- and docking-induced layer reconstruction. The reconstruction dramatically lowers the OER overpotential to 240 mV at 10 mA/cm2 and the Tafel slope to 33 mV/dec, making Fe-Bir the best of all the reported Bir-based catalysts, even on par with the best transition-metal-based OER catalysts. Experimental characterizations and molecular dynamics simulations elucidate that the catalyst features active Fe(III)-O-Mn(III) centers interfaced with ordered water molecules between neighboring layers, which lower reorganization energy and accelerate electron transfer. DFT calculations and kinetic measurements show non-concerted PCET steps conforming to a new OER mechanism, wherein the neighboring Fe(III) and Mn(III) synergistically co-adsorb OH* and O* intermediates with a substantially reduced O-O coupling activation energy. This work highlights the importance of elaborately engineering the confined interlayer environment of birnessite and more generally, layered materials, for efficient energy conversion catalysis.

Prediction of two-dimensional monolayer C2O2Fe with chiral magnetic and ferroelectric orders.

Low-dimensional multiferroics are highly desired for applications and contain exotic physical properties. Here we predict a two-dimensional material, C2O2Fe monolayer, through Fe intercalation in the graphene oxide monolayer. The crystal stable texture, chiral spin order, and ferroelectric polarization of the C2O2Fe monolayer are theoretically studied by considering the electron on-site Coulomb interaction and spin orbit coupling, which also manifests the ferroelectric polarization and reversal barrier at 30% biaxial tensile strain comparable with the other two-dimensional ferroelectric materials, such as GeS and GeSe. Moreover, first-principles calculations show that the polarization flipping is accompanied by spin orientation reversal, when the ferroelectric polarization is upward to the plane, a clockwise chiral antiferromagnetic ground state is obtained, while when the polarization is downward, the monolayer shows the anticlockwise chiral antiferromagnetic structure. In this sense, a strong electrically controlled magnetism exists in the designed C2O2Fe monolayer film.

Crosslinked chitosan-montmorillonite biocomposite with Fe intercalation: Enhancing surface chemistry for improved phosphate adsorption

This research incorporates iron-loaded crosslinked chitosan (CS) polymeric structure into the interlayer lattice space of Montmorillonite clay (MT) to enhance the phosphate adsorption capacity of MT. The synthesized Fe-loaded crosslinked chitosan montmorillonite composite (Fe-CS-MT) is evaluated effectively for phosphate removal from aqueous media. Batch adsorption experiments optimized the influence of adsorption parameters, i.e., contact time (50 min), solution pH (3), and adsorbent dosage (2 g L−1) for phosphate removal. The experimental results of equilibrium and kinetic studies indicated that phosphate adsorption on Fe-CS-MT follows Pseudo-second-order kinetic and Freundlich isotherm models with a high degree of accuracy. A series of analytical tools used to profile the investigated material's surface features involves CHNS Analyser, SEM-EDX, FTIR, XRD, XRF, UV-Visible Spectrophotometer, TGA, DSC, and surface analysis. The calculations of the thermodynamic study confirmed the endothermic and spontaneous nature of the phosphate adsorption process. This study presents an eco-friendly adsorbent tested in natural conditions to assess the feasibility of removing phosphate from an aqueous phase.

Magnetic response and electronic states of well defined Graphene/Fe/Ir(111) heterostructure

We investigate a well defined heterostructure constituted by magnetic Fe layers sandwiched between graphene (Gr) and Ir(111). The challenging task to avoid Fe-C solubility and Fe-Ir intermixing has been achieved with atomic controlled Fe intercalation at moderate temperature below 500 K. Upon intercalation of a single ordered Fe layer in registry with the Ir substrate, an intermixing of the Gr bands and Fe $d$ states breaks the symmetry of the Dirac cone, with a downshift in energy of the apex by about 3 eV, and well-localized Fe intermixed states induced in the energy region just below the Fermi level. First principles electronic structure calculations show a large spin splitting of the Fe states, resulting in a majority spin channel almost fully occupied and strongly hybridized with Gr $\ensuremath{\pi}$ states. X-ray magnetic circular dichroism on the Gr/Fe/Ir heterostructure reveals an ordered spin configuration with a ferromagnetic response of Fe layer(s), with enhanced spin and orbital configurations with respect to the bcc-Fe bulk values. The magnetization switches from a perpendicular easy magnetization axis when the Fe single layer is lattice matched with the Ir(111) surface to a parallel one when the Fe thin film is almost commensurate with graphene.

Orbital Selectivity and magnetic ordering in Fe intercalated dirac semimetal Bi2Se3

In this paper we investigate the intercalation effects of Iron (Fe) in the van der Waals gap of Bi2Se3 on the magnetic and transport properties using first-principles band structure estimations combined with dynamical mean-field theory. The Dirac cone in the band structure of parent Bismuth Selenide is modified via Fe intercalation at moderate densities. Further inclusion of electronic correlations found to result in the emergence of novel and exotic properties in an intercalated Bi2Se3. Accompanied by unconventional structural effects, the onset of an orbital selective metal insulator transition in the Fe 3d orbitals brings about a magnetic phase transition in the Fe intercalated Bi2Se3. Additionally we have explored the dependency of the electron-electron correlations on the magnetic ordering and the effects of intercalation in establishing new physical properties.

Fe-intercalated few layers reduced graphene oxide: A unique material for supercapacitor applications

Although intensive research has been carried out on composite materials containing transition metal (TM) oxides and graphene for supercapacitor application, the field remains totally unexplored to intercalate TM atoms in few layer reduced graphene oxide (rGO) to design high performance supercapacitors. The major advantages are the enhancement in porosity and formation of trap states at the Fe sites for better charge storage capacity. Therefore, in the present work, Fe-intercalated few layer rGO samples are synthesized to enhance the interlayer separation from 0.34 to ∼1 nm. The enhancement of interlayer separation is characterized by x-ray diffraction, which shows a single peak at a 2θ value of 8.7°, indicating the layered type material with an interlayer separation of 1 nm. Large enhancement in specific capacitance to about 896 F/g and a high energy density of 31 W h/kg is observed in this highly porous material. All these results of enhancement in specific capacitance and energy density are explained on the basis of trap states created at the Fe sites and large enhancement in porosity due to Fe intercalation. Cyclic stability to about 85% after 8000 cycles is also verified. Quantitative evaluation of trap states and modification of charge transport are observed. Due to trap centers, a high value of dielectric permittivity is achieved.

Nontrivial spatial dependence of the spin torques in L10 FePt-based tunneling junctions

We present an {\it ab-initio} study of the spin-transfer torque in a Fe/MgO/FePt/Fe magnetic tunnel junctions. We consider a FePt film with a thickness up to six unit cells, either in direct contact with the MgO spacer or with an intercalated ultra-thin Fe seed layer. We find that in the FePt layer the torque is not attenuated as strongly as in the case of pure Fe. Moreover, in FePt the torque alternates sign at the Fe and Pt atomic planes throughout the stack for all FePt thicknesses considered. Finally, when Fe is intercalated between MgO and L$1_0$-FePt, the torque is sharply attenuated and it is transferred to FePt only for a Fe seed layer that is less than two-atomic-planes thick. We attribute these features to the different spatial profiles of the exchange and correlation field and the induced non-equilibrium spin accumulation. The calculated tunnelling magneto-resistance of the Fe/MgO/FePt/Fe junctions studied is enhanced with respect to the one of Fe/MgO/Fe, while it is reduced with Fe intercalation. Our work shows that L$1_0$-FePt junctions can be promising candidates for current-operated magnetic devices and that the magnetic texture at the atomic scale has an important effect on the spin transfer torque.

Insight into water oxidation activity enhancement of Ni-based electrocatalysts interacting with modified carbon supports

Water splitting is a clean and renewable way to produce hydrogen, and developing an efficient water oxidation electrocatalyst is crucial to overcome the slow kinetics and large overpotential of the oxygen evolution reaction (OER) in water electrolysis. In this work, we demonstrate that OER activity of an electrodeposited Ni catalyst can be influenced by a support material, and electron transfer between the Ni-based catalyst and the support is proposed to increase the oxidation states of Ni and thus contribute to enhancing its intrinsic OER activity. When a Ni catalyst layer is deposited using a carbon-based powder support instead of an expensive Au foil, the overpotential decreased by more than 50 mV at 10 mA/cm2 due to the synergic effect of the increased surface area and the modified Ni electronic states. In addition, compared with carbon powder supports, Fe and N doped carbon (Fe-N-C) is found to provide particularly more efficient support for the Ni OER catalyst; however, according to electrochemical measurement results, there is no indication of additional Fe intercalation. X-ray photoelectron spectroscopy (XPS) analysis shows the highest binding energy of Ni particularly on the Fe-N-C, suggesting facile electron transfer from Ni to the Fe-N-C interface.

ChemInform Abstract: From WCl6 to WCl2: Properties of Intermediate Fe—W—Cl Phases.

AbstractOngoing reduction of WCl6 by elemental Fe intercalation successively results in the compounds FexWCl6, FeW2Cl10, Fe2W2Cl10, (Fe,W)1‐xCl2, and FeW6Cl14.

The dynamics of Fe intercalation on pure and nitrogen doped graphene grown on Pt(111) probed by CO adsorption

Abstract In this paper we compare by temperature programmed desorption the intercalation rate of Fe nanoparticles supported on pure and nitrogen doped graphene grown on Pt (111). Carbon monoxide desorption from Fe sites is used to probe the overall quantity of Fe present onto the graphene surface. We do not observe any appreciable difference of CO desorption temperature induced by N functionalities of graphene; however we notice a faster intercalation for Fe nanoparticles deposited on N-doped graphene with respect the those supported on pure graphene. We relate this phenomenon to nanoholes created by pyridinic and pyrrolic functionalities and/or to the lower bond enthalpy of C N with respect to C C bonds. Scanning tunneling microscopy and X-ray photoelectron spectroscopy are used as complementary techniques to identify the N functionalities and to characterize the morphological defectivity of the graphene films.

Graphene as a surfactant for metal growth on solid surfaces: Fe on graphene/SiC(0001)

X-ray photoelectron spectroscopic and scanning tunneling microscopic results demonstrate that annealing of Fe/carbon-rich 6H-SiC(0001) surface between 650 and 750 °C leads to Fe intercalation under the surface carbon layer. Accompanied with the metal intercalation, the carbon nanomesh surface was transformed into a graphene surface. Moreover, the formed graphene layers always float out to the topmost surface even after deposition of more than 10 monolayer Fe, acting as a surfactant. Using graphene as the surfactant may not only promote the 2D growth but also can improve the film performance considering that graphene is stable and robust.

Anomalous Transport Properties in Fe Intercalation Compound Fe x TiSe2 Single Crystals

The transport and magnetic properties of single-crystalline Fe-intercalation-compound Fe x TiSe2 have been compared with the transport properties of single-crystalline Ti-self-intercalation-compound Ti x TiSe2. At low concentration of intercalated guest atoms, Fe x TiSe2 exhibits carrier localization behavior without magnetic ordering, while Ti x TiSe2 shows an itinerant behavior. The superstructure and the carrier localization observed in Fe x TiSe2 single crystals simultaneously disappear at the critical concentration x c∼0.07, which agrees well with theoretical value based on a percolation theory. Fe intercalation compounds show paramagnetism and nonexistence of magnetism is attributed to the large distance between guest Fe atoms. We discuss the effect of guest intercalation on the stability of superstructure formed in the host.

Transport and magnetic properties ofFexVSe2 (x = 0–0.33)

We present the results of the effect of Fe intercalation on the structural, transport and magnetic propertiesof 1T-VSe2. Intercalation of iron suppresses the charge density wave transition at 110 K in1T-VSe2. And for more than 10% Fe concentration a new kind of first-order transitionappears below 160 K in our resistivity results. The transition becomesstronger with a broad hysteresis (80–160 K) for 33% Fe intercalation. Theanomalies are absent in the thermopower measurements of polycrystallineFexVSe2 compounds(x = 0–0.33). The susceptibility measurements between 2 and 300 K and the magnetization in ahigh magnetic field up to 14 T at 2 K are reported. The Fe atoms are in the low-spin (S = 1/2) stateof Fe3+ and the compounds show the absence of any magnetic order at low temperatures.

Modification of electronic, optical, and magnetic properties of titanate nanotubes by metal intercalation

The electronic, optical, and magnetic properties of H(2)Ti(3)O(7) are investigated by first-principles density function theory calculations, and also the modifications of these properties by metal intercalation in H2Ti3O7. It is shown that the band gap of H(2)Ti(3)O(7) may be significantly reduced by Fe or Ni intercalation, and that the intercalated Fe or Ni may form a one-dimensional (1D) channel via overlapping 3d orbitals along the [010] direction in the interlayer region. These overlapping 3d orbitals result in an extended band within the band gap region of H(2)Ti(3)O(7) and below its Fermi level, and this band in turn results in a low effective mass for hole transport along the 1D channel and a large magnetic moment for the Fe or Ni intercalated material.