Iron Thin Films Research Articles

Tuning the magnetic properties of Fe thin films with RF-sputtered amorphous carbon

RF-sputtered amorphous carbon (a-C) offers a simple and cheap pathway to tune the magnetic properties of transition metal thin films for magnetic memories and different spintronic applications. This paper describes changes in the magnetic properties of iron thin films with a-C overlayers. In as-deposited samples, hybridisation and intermixing at the Fe/a-C interface leads to magnetic softening (Liu et al., 2006) [1], with a reduction in the coercive field (Hc) up to a factor of five for Fe/a-C/Fe trilayers, and a 10–30% lower saturation magnetization as a function of the metal film thickness. After annealing at 500 °C, inter-diffusion and graphitization of the carbon layer results in up to a factor five increased coercivity due to increased pinning as shown via Kerr microscopy. Therefore, RF-sputtered carbon overlayers and post-processing can tune the anisotropy and domain configuration of metallic thin films in a synthesis methodology that is simple, cheap and sustainable.

Effect of Crack Defects on Magnetostriction and Magnetic Moment Evolution of Iron Thin Films.

Molecular dynamics simulations of body-centered cubic (bcc) iron thin films with crack defects were carried out by adopting methods of EAM (Embedded Atom Method) potential, spin/exchange potential and spin/neel potential. In this article, the effects of the variation of distance between two crack defects and their directions on the magnetostrictive properties of the thin films are studied, and the corresponding microscopic mechanism is also analyzed. The results show that the defects affect the atomic magnetic moment nearby, and the magnetostrictive properties of thin iron films vary with the direction and spacing of the crack defects. If the defect spacing is constant, the iron model with crack perpendicular to the magnetization direction has stronger magnetostriction than that of parallel to the magnetization direction. The variation of the defect spacing has a great influence on the magnetostrictive properties of the iron model with crack direction parallel to magnetization direction, but it has a small effect on another perpendicular situation. The atoms between the defects may move, but if the defect spacing increases to a certain value, then none of the atoms will move.

Spectrum evolution and chirping of laser-induced spin wave packets in thin iron films

We present an experimental study of ultrafast optical excitation of magnetostatic surface spin wave (MSSW) packets and their spectral properties in thin films of pure iron. As the packets leave the excitation area and propagate in space, their spectra evolve non-trivially. Particularly, low or high frequency components are suppressed at the border of the excitation area depending on the orientation of the external magnetic field with respect to the magnetocrystalline anisotropy axes of the film. The effect is ascribed to the ultrafast local heating of the film. Furthermore, the time resolution of the implemented all-optical technique allows us to extract the chirp of the MSSW packet in the time domain via wavelet analysis. The chirp is a result of the group velocity dispersion of the MSSW and, thus, is controlled by the film's magnetic parameters, magnetization and anisotropy, and external field orientation. The demonstrated tunable modulation of MSSW wave packets with femtosecond laser pulses may find application in future magnonic-photonic hybrid devices for wave-based data processing.

Automated processing of environmental transmission electron microscopy images for quantification of thin film dewetting and carbon nanotube nucleation dynamics

Scalable production of carbon nanotubes (CNTs) requires catalysts and reaction conditions that provide high nucleation efficiency. In situ characterization methods such as environmental transmission electron microscopy (ETEM) can reveal fundamental mechanisms of synthesis, but to date have primarily provided qualitative observations on small sample sizes. Here, quantitative analysis is performed using high-resolution, high-rate video capture of ETEM experimentation coupled with automated image processing, involving computer vision algorithms and convolutional neural networks. By this approach, we detect distinct nanoparticle formation from an alumina-supported iron thin film and subsequent CNT nucleation from the nanoparticles. The statistical summary of particles in each video shows that, compared to a H2-only atmosphere, pretreatment of the catalyst with carbon added to the H2 atmosphere results in a smaller average particle diameter, a 2-fold increase in particle density (to 5300 particles/μm2), a 3-fold increase in CNT nucleation efficiency (to 92%), and more than a 5-fold increase in CNT density (to 4800/μm2). Addition of carbon during exposure to H2 is also more effective than NH3 at dewetting the catalyst film and increasing the CNT nucleation efficiency, in spite of NH3 being a stronger reducing agent for iron. Insights from this study are applicable to improving CNT yield and productivity in both batch-style and continuous processes.

Iron carbide formation on thin iron films grown on Cu(1 0 0): FCC iron stabilized by a stable surface carbide

Thin iron films evaporated onto Cu(100) were carburized using ethylene to produce iron carbide surfaces for use as model systems in experimental research. XPS and AES confirm that ethylene dissociation produces a pure iron carbide. A maximum of 0.5 ML carbon can be deposited for film thicknesses below 12 ML where Fe grows as γ-iron (FCC). For thick, BCC-Fe(110) films, post-treatment with ethylene leads to carbon coverages beyond 0.5 ML where some carbon diffuses into the bulk. The film remains α-iron (BCC) and a different surface carbide with a (4 × 3) unit cell is found. On the thin FCC-Fe(100) films, carbon reconstructs the surface into a p4g(2 × 2)-Fe2C layer which has a special stability and acts as a carbon trap that prevents carbon diffusion into the bulk. Fe2C is thermally stable up to 700 K above which Fe diffuses into the copper substrate while leaving graphitic carbon behind. Carbon segregates to the surface during evaporation of iron on top of an Fe2C-covered FCC-Fe film and causes the film to retain the FCC structure up to a thickness of at least 30 ML, far beyond 12 ML where BCC-Fe forms on Cu(100) in absence of surface carbon.

Iron Carbide Formation on Thin Iron Films Grown on Cu(100): Fcc Iron Stabilized by a Stable Surface Carbide

Iron Carbide Formation on Thin Iron Films Grown on Cu(100): Fcc Iron Stabilized by a Stable Surface Carbide

Effect of defects on magnetostriction and magnetic moment evolution of iron thin films

Magnetostrictive materials have broad application prospects in sensing, control, energy conversion, and information conversion. The improving of the performances and applications of such materials has become a research hotspot, but defects will inevitably appear in the preparation and use of materials. In this study, the magnetostrictive structure model of iron elemental material with no defect or hole defect or crack defect is established by the molecular dynamics method. The influences of different defects on the magnetostrictive behavior of iron thin films are analyzed, and the mechanism of the influence of defects on the magnetostrictive behavior is depicted from the perspective of atomic magnetic moment. The results show that the films with 60 × 2 × 1 defects in the center are the easiest to reach saturation magnetostriction, and the magnetostriction is the least after reaching saturation, with respect to the films without defects. The films with 10 × 10 × 1 and 2 × 60 × 1 defects in the center require a larger magnetic field to approach to saturation, and the magnetostriction of the film with 2 × 60 × 1 defects in the center reaches a maximum value after saturation. This is because the defects will affect the magnetic moment of the surrounding atoms and make them deflect to the direction parallel to the defects, thus affecting the magnetostriction of the iron thin film. Among them, the hole defects have less influence on the magnetostriction, while the crack defects have stronger influence on the magnetostriction. The direction of the crack also has an effect on the magnetostriction of Fe thin film. When the crack is parallel to the direction of magnetization, the maximum magnetostriction of the film in the direction of magnetization from the initial state to the saturation of magnetization will decrease. When the crack is perpendicular to the direction of magnetization, the maximum magnetostriction of the film in the direction of magnetization from the initial state to the saturation of magnetization will increase. These results suggest that the defects affect the magnetostriction of the model as a whole during magnetization by affecting the initial magnetic moment orientation of the surrounding atoms.

Dislocation Loop Generation Differences between Thin Films and Bulk in EFDA Pure Iron under Self-Ion Irradiation at 20 MeV

In the present investigation, high-energy self-ion irradiation experiments (20 MeV Fe+4) were performed on two types of pure Fe samples to evaluate the formation of dislocation loops as a function of material volume. The choice of model material, namely EFDA pure Fe, was made to emulate experiments simulated with computational models that study defect evolution. The experimental conditions were an ion fluence of 4.25 and 8.5 × 1015 ions/cm2 and an irradiation temperature of 350 and 450 °C, respectively. First, the ions pass through the samples, which are thin films of less than 100 nm. With this procedure, the formation of the accumulated damage zone, which is the peak where the ions stop, and the injection of interstitials are prevented. As a result, the effect of two free surfaces on defect formation can be studied. In the second type of experiments, the same irradiations were performed on bulk samples to compare the creation of defects in the first 100 nm depth with the microstructure found in the whole thickness of the thin films. Apparent differences were found between the thin foil irradiation and the first 100 nm in bulk specimens in terms of dislocation loops, even with a similar primary knock-on atom (PKA) spectrum. In thin films, the most loops identified in all four experimental conditions were b ±a0<100>{200} type with sizes of hundreds of nm depending on the experimental conditions, similarly to bulk samples where practically no defects were detected. These important results would help validate computational simulations about the evolution of defects in alpha iron thin films irradiated with energetic ions at large doses, which would predict the dislocation nucleation and growth.

Synthesis of magneto-dielectric coatings in electron-beam produced plasma in medium vacuum

Using sequential electron-beam evaporation of high-temperature dielectric (alumina ceramic) and magnetic (iron) targets in various gas atmospheres (helium, air, and oxygen) in medium vacuum (5–8 Pa), magneto-dielectric coatings with thickness of around 2 μm were deposited from a multicomponent beam plasma at a deposition rate of 0.2–0.3 μm/min. The coating magnetic properties were explored by the ferromagnetic resonance technique, revealing that their effective magnetization depends on the type of operating gas and varied from 4.2 to 6.8 kGs (for deposition in helium) to 0.3 kGs (in oxygen), which is characteristic of oxide ferromagnetic materials and is considerably lower than the corresponding value (∼22 kGs) for thin iron films formed by vacuum arc deposition in high vacuum. X-ray structural analysis of coatings deposited in medium vacuum in helium showed that the magnetic layer has a magnetite (Fe3O4) structure. The alumina ceramic layer provides the dielectric properties of the magneto-dielectric coating; a relative dielectric constant of 6.0 and a conductivity of 8.4 mS/m were achieved.

Pinpointing active sites for water splitting

Microscopic defects on a catalyst made of carbon and iron actively drive the hydrogen evolution reaction, one of the key steps in liberating hydrogen from water, according to a study that combines electrochemical analysis with atomic resolution microscopy ( Nat. Catal. 2021, DOI: 10.1038/s41929-021-00682-2 ). If scientists can find catalysts that efficiently split water into hydrogen and oxygen , then the oceans could serve as a nearly limitless supply of clean-burning, carbon-free hydrogen fuel for transportation and other uses. Precious metals work well as catalysts, but they’re expensive. So a team led by Stefano Agnoli and Gaetano Granozzi of the University of Padua examined inexpensive model catalysts consisting of thin films of graphene and iron. Sandwiches made from those films can be highly active electrocatalysts for hydrogen evolution, but how they work is unclear. The researchers used electrochemical scanning tunneling microscopy to examine the films while they mediated the catalytic

Aqueous Sol-Gel Synthesis of Different Iron Ferrites: From 3D to 2D.

In this study, an aqueous sol-gel synthesis method and subsequent dip-coating technique were applied for the preparation of yttrium iron garnet (YIG), yttrium iron perovskite (YIP), and terbium iron perovskite (TIP) bulk and thin films. The monophasic highly crystalline different iron ferrite powders have been synthesized using this simple aqueous sol-gel process displaying the suitability of the method. In the next step, the same sol-gel solution was used for the fabrication of coatings on monocrystalline silicon (100) using a dip-coating procedure. This resulted, likely due to substrate surface influence, in all coatings having mixed phases of both garnet and perovskite. Thermogravimetric (TG) analysis of the precursor gels was carried out. All the samples were investigated by X-ray powder diffraction (XRD) analysis. The coatings were also investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Mössbauer spectroscopy. Magnetic measurements were also carried out.

Advanced, Kerr-microscopy-based MOKE magnetometry for the anisotropy characterisation of magnetic films

An advanced wide-field Kerr microscopy and magnetometry approach for the investigation of magnetic anisotropy in magnetic films is demonstrated. We have analytically analysed the longitudinal Kerr contrast in a wide-field magneto-optical Kerr microscope, specifically its dependence on the light polarisation direction and the plane of incidence and verified it experimentally. While normally the sensitivity direction (i.e. the direction of maximum contrast for antiparallel domains) of the longitudinal Kerr effect is along the plane of incidence for both, p - and s-polarized light, we found a deviation of the sensitivity direction from the incidence plane for p-polarised light. Based on a multi-component Kerr imaging technique we have developed a fully automated procedure for the measurement of magnetisation reversal loops along arbitrary in-plane field directions for magnetic films with in-plane anisotropy that does not require any mechanical adjustment of the system or sample displacement. The method is applied to the investigation of the magnetic anisotropy of a sputtered iron thin film. Additionally, a sample holder was introduced, which allows for the application of mechanical stress onto magnetic films due to substrate bending, and its applicability to the stress manipulation of the anisotropy direction was demonstrated for a nickel-iron film.

Comparing temperature convergence of shocked thin films of tin and iron to a bulk temperature source

An outstanding challenge in developing a complete equation of state for materials at elevated pressure and temperature is a robust method of determining the bulk temperature state under dynamic conditions. In metals, the determination of bulk temperature states by optical pyrometry is complicated by the small optical depth and thermal conduction effects. These effects lead to observed temperatures differing by 20% or more from the bulk temperature state. In this work, we show the presence of thermal conduction effects in temperature measurements of tin and iron coatings during dynamic compression experiments. We demonstrate that tin, in contrast to iron, coatings can fail to converge to a bulk temperature source over the time scale of the experiment, requiring the experimenter to modify assumptions, design, or analysis. This work bounds thermal transport at shocked conditions.

ELECTROCHEMICAL SYNTHESIS OF IRON MONOSELENIDE THIN FILMS

In the presented research work, the kinetics and mechanism of the deposition process of thin iron, selenium and Fe-Se films have been studied by recording a cyclic and linear polarization curves by potentiodynamic method using Pt and Ni electrodes. Individual and co-deposition potential areas of the components of the electrolyte on the Pt electrode were determined. In order to determine the optimal electrolysis mode and electrolyte composition, the effect of various factors (concentration of initial components, temperature, etc.) on the co-electrodeposition process of Fe-Se was studied. In addition, Fe-Se samples deposited on the surface of Ni electrodes were thermally treated at 4500C and studied by SEM and X-ray phase analysis methods. Elemental analysis of the films shows that they contain 42.2% Fe and 57.8% Se.

Molecular dynamics study on the effect of defects on magnetostriction of iron thin films

磁致伸缩材料在传感、控制及能量与信息转换等领域应用前景广阔，此类材料的性能提升及工程应用已成为研究热点，但材料在制备与使用中不可避免会出现缺陷。本文以常用的铁磁性材料铁单质为研究对象，采用分子动力学方法分别建立无缺陷、孔洞缺陷与裂纹缺陷的铁单质磁致伸缩结构模型，分析了缺陷形式对铁单质薄膜磁致伸缩行为的影响，并从微观原子磁矩角度解释缺陷对磁致伸缩行为的影响机理。结果表明：缺陷会对其周围的原子磁矩产生影响，从而影响铁单质薄膜磁致伸缩，其中孔洞形缺陷对磁致伸缩的影响较小，裂纹形缺陷对磁致伸缩的影响较大。裂纹的方向会影响铁单质薄膜的磁致伸缩，与磁化方向平行的裂纹会降低材料在磁化方向上由初始状态至磁化达到饱和的最大磁致伸缩量；与磁化方向垂直的裂纹会提高材料在磁化方向上由初始状态至磁化达到饱和的最大磁致伸缩量。

Detection of femtosecond spin voltage pulses in a thin iron film.

We present experimental evidence of a spin voltage—a difference between the chemical potentials of the two spin directions—in a thin iron film based on spin- and time-resolved photoemission spectroscopy. This voltage is the driving force for a spin current during the ultrafast demagnetization of the sample. The observed magnitude is on the order of 50 mV, a value that is quite consistent with predictions based on particle conservation and persists for approximately 100 fs.

Development of iron thin films by electron beam physical vapour deposition (EBPVD): A Review

This review paper study about the possibilities of results obtained from conducted experiment of iron (Fe) thin films by electron beam physical vapor deposition (EBPVD). Previous studies showed that by exposing the substrate of the thin film to pre-heat environment, the changes of morphology and adatom mobility is expected. Furthermore, annealed influence in the thin film also will give better-quality thin films as the surface are expected to be smoother and flat. Three different annealed temperature is conducted on the samples, which are 400°C, 800°C and 1200°C. Structural changes such as transition from alpha phase to beta phase, is possible due to the presence of high temperature.

Looking at Electron Dynamics to Better Understand Photo-Active Materials

The generation of free and energetic electrons is the key to the next generation of photo-voltaic and photo-catalysts. In order to produce such electrons, the sunlight is so far the most promising sustainable source of energy. However, the conversion efficiency from light to the liberation of a functional electron depends on numerous factors and processes that are difficult to account for. One of the reasons is the difficulty of monitoring the early electron dynamics such as the charge separation event and the subsequent electronic relaxation and migration. Here, I propose the use of ultrafast transient absorption spectroscopy to watch these electronic events “live” in the femto- to nano-seconds (10-15-10-9 sec.) time scales. In this presentation, I will demonstrate this technique on iron and copper oxides thin films. In this study, we produce ultrashort laser pulses to mimic sunlight and trigger charge separations that ultimately lead to the generation of the reactive oxygen species that confer the films their antibacterial properties. With this technique, we are able to harvest information such as the charge separation efficiency, electron dynamics, excited state’s bandgap energy, and even material deformation upon photo-excitation, all of which are key to understand, control and enhance the conversion process.

Shear Deformation Helps Phase Transition in Pure Iron Thin Films with “Inactive” Surfaces: A Molecular Dynamics Study

In a previous study, it was shown that the (111)fcc, (110)fcc and (111)bcc free surfaces do not assist the phase transitions as nucleation sites upon heating/cooling in iron (Fe) thin slabs. In the present work, the three surfaces are denoted as “inactive” free surfaces. The phase transitions in Fe thin films with these “inactive” free surfaces have been studied using a classical molecular dynamics simulation and the Meyer–Entel potential. Our results show that shear deformation helps to activate the free surface as nucleation sites. The transition mechanisms are different in dependence on the surface orientation. In film with the (111)fcc free surface, two body-centered cubic (bcc) phases with different crystalline orientations nucleate at the free surface. In film with the (110)fcc surface, the nucleation sites are the intersections between the surfaces and stacking faults. In film with the (111)bcc surface, both heterogeneous nucleation at the free surface and homogeneous nucleation in the bulk material are observed. In addition, the transition pathways are analyzed. In all cases studied, the unstrained system is stable and no phase transition takes place. This work may be helpful to understand the mechanism of phase transition in nanoscale systems under external deformation.

Magnetisation and magnetic anisotropy of ion beam synthesised iron nitride

We report the effects of implantation-induced-sputtering in determining the true magnetisation of iron nitrides formed by nitrogen implantation into iron films and the changes subsequently observed in their magnetic anisotropy. Iron thin films (40 nm) capped with gold layers were synthesized by ion beam sputtering. Nitrogen was implanted onto the thin film to a dose of 7 × 1016 cm−2. Dynamic ion–solid interaction simulations calculate the average nitrogen concentration within the iron thin films to be 13 at.%. Ion beam analysis was used to evaluate the composition and depth profile of the thin films before and after implantation. Cross-sectional transmission electron microscopy helped in identifying the implantation induced effects at the surface and interface of the thin film structure. Magnetisation measurements show that nitrogen implantation enhances the magnetisation of thin films and reduces their in-plane magnetic anisotropy. High resolution TEM and magnetisation results suggest formation of α’/α”-Fe16N2 with large magnetic moments and perpendicular magnetic anisotropy. The enhancement in magnetisation of the thin film with and without considering the sputtering losses is determined to be 15% and 5%, respectively. Our review of literature shows that underestimating the sputtering losses from implantation leads to reporting of inconsistent and reduced magnetic moments for Fe16N2.