Fe Layer Thickness Research Articles

An investigation on anisotropic FMR linewidth in Fe ultrathin film grown on GaAs substrate

Understanding the dynamic properties of magnetic films with the thickness down to nanometer scale is of both fundamental interests, as well as of great importance for the development of spintronic devices. In this study, we report the emergence of anisotropic magnetization dynamics by exploring a quasi-two-dimensional single-crystalline Fe/GaAs(001) interface with varying Fe layer thicknesses ranging from 0.7 to 3.0 nm using ferromagnetic resonance (FMR) technique. Various linewidth contributions, including intrinsic isotropic Gilbert damping, extrinsic inhomogeneous broadening and anisotropic two-magnon scattering are considered for the accurate fitting. We analyze and discuss the different mechanisms of linewidth and its field orientation dependence. Especially we propose a phenomenological expression for the anisotropic two-magnon scattering linewidth consisting of two-fold and four-fold symmetry parameters, which achieves a better understanding of the mechanism of anisotropic two-magnon scattering linewidth in the single crystal ultrathin film. Our analytical methods and results not only provide an effective approach for spin dynamic study in spintronics, but also enrich the understanding of the mechanisms of magnetization relaxation in other ferromagnetic metal/semiconductor interface systems.

Regulating interfacial exchange coupling in perpendicular magnetized Fe/DO22-Mn3Ga bilayer films

Manganese gallium alloy with DO22-type chemical ordering (DO22-Mn3Ga) thin film represents an intriguing candidate for fabricating the fundamental composition of magnetic devices. In this paper, we prepare the Fe/DO22-Mn3Ga composite films on thermal MgO (100) substrates with different annealing temperatures and report the interfacial exchange coupling between Fe and DO22-Mn3Ga bilayers. Fe layer thickness and annealing temperature are predominant in regulating the nature and strength of interfacial exchange coupling. It is found that there is a ferromagnetic coupling between Fe and DO22-Mn3Ga layers. Their exchange coupling strength can be regulated by changing the Fe soft magnetic layer thickness in a reasonable range. Additionally, the interface diffusion generated from heat treatment induces to change of the nature of exchange coupling. It is possible that Fe replaces Mn site in the DO22-Mn3Ga unit cell due to smaller atomic radius and higher electronegativity compared with Mn. Antiferromagnetic coupling from annealed Fe/DO22-Mn3Ga film with high perpendicular magnetic anisotropy is technologically important to research synthetic antiferromagnetic structure for spin-transfer-torque magnetoresistive random access memory. Our works is helpful for the exploration of interfacial science and development of magnetic devices.

Effect of iron layer thickness on the interlayer exchange coupling in Fe/MgO (001) superlattices

We describe the effect of the Fe layer thickness on the antiferromagnetic interlayer exchange coupling in [Fe/MgO]N superlattices. An increase in coupling strength with increasing Fe layer thickness is observed, which highlights the need for including the extension of both layers when discussing the interlayer exchange coupling in superlattices. Published by the American Physical Society 2024

Deuterium permeation and lithium‑lead corrosion behaviors of ceramic‑iron joint coating

In fusion reactor blanket design, the main challenges are to control the permeation of tritium and prevent the corrosion of the structural materials. This study focuses on investigating the behavior of ceramic‑iron joint coatings in terms of deuterium permeation and Li-Pb corrosion aiming to develop effective barriers against permeation while providing corrosion protection. The research involved fabricating ZrO2 and Fe2O3 ceramic coatings on F82H steel substrates using metal-organic decomposition followed by joining the coated samples with Fe foils using a hot press machine. Deuterium permeation measurements were conducted to assess the effectiveness of the coating, and liquid Li-Pb exposure tests in a flow environment were performed to evaluate its resistance against corrosion. The results showed that the coating reduced deuterium permeation flux by a factor of 2000 at 400 °C and 7000 at 550 °C compared to uncoated samples suggesting an improved crystallinity or grain growth without degradation due to the joining process. Furthermore, the corrosion layers formed on the surface of the Fe layer after the flowing Li-Pb exposure test. Although this layer gradually decreased in thickness over time while not significantly affecting the underlying Fe layer's thickness. This observation indicates that the corrosion layer performed mitigating the corrosion rate of the Fe layer. This paper aims to demonstrate how ceramic‑iron joint coatings can be compatible with the advanced fusion reactors.

Modeling of negative capacitance underlap graded-channel junction accumulation mode junctionless FET in nano-scale regime

Analytical modeling of negative capacitance (NC) graded-channel (GC) underlap junction accumulation mode (JAM) JL-FET is presented in this literature. Here, the surface potential, threshold voltage, sub-threshold drain current, sub-threshold swing (SS) and DIBL are obtained by solving the 2D Poisson's equation and Landau-Khalatnikov (LK) equation simultaneously. Performances of the proposed NC-GC-JAM-JL-FET is analyzed in detail for the variations in FE-layer thickness, gate-length, underlap length, graded channel ratio and Si-film thickness. The proposed model is calibrated with the experimental data to establish its acceptability. The proposed device is also simulated in the Silvaco ATLAS device simulator, which shows very good agreement with the analytical model. The present paper establishes the remarkable prospect of the proposed architecture to be operated for low-power application in nano-scale regime.

Engineering negative differential resistance in negative capacitance Quad-FinFET

In this work, a systematically analysis of the Negative Capacitance (NC) Quad-FinFET structure is carried out where we determine the optimal FE layer thickness that enables hysteresis-free transfer characteristics. However, negative differential resistance (NDR) is introduced along with the increased FE-layer thickness, which is not desirable for application in analogcircuits. Through the implementation of an asymmetric drain length extension and a high-k Si3N4 spacer, negative differential resistance (NDR) can be mitigated. In addition, the relatively poor analog performance generally seen in conventional FinFET structures are overcome in the drain engineered NC Quad-FinFET structure with gate spacer resulting in significant improvement in performance parameters such as transconductance, output conductance and intrinsic gain. The integration of NC Quad-FinFET as a digital inverter is carried out where the circuit propagation delay is decreased by 27.65% with drain length extension and inclusion of Si3N4 spacer. Thus, through these device optimization techniques, the NC Quad-FinFET structure shows significant improvement in both analog and digital device performance parameters.

Molecular dynamics studies of the effect of intermediate Fe layer thickness on the enhanced strength and ductility of Cu/Fe/Ni multilayer

The synergistic strength-ductility is very important for composite materials. In this work, we studied the effect of intermediate layer thickness on the mechanical properties of Cu/Fe/Ni multilayer by introducing harder intermediate layer and non-coherent interface using molecular dynamics simulation, and revealed the relationship between the deformation mechanism and the strength-ductility from atomic scale. The results show that the yield strength and flow stress increase with increasing Fe layer thickness, but the tensile strain is opposite. Plastic deformation of all models are triggered by slipping of misfit partial dislocation originating from the decomposition of perfect dislocation on semi-coherent interface. However, the addition of Fe layer and non-coherent interface increases the resistance of dislocation crossing interface, and changes the dominant deformation mechanism from Shockley partial dislocation slipping to deformation twinning migration, thus improving the strength and ductility of multilayer. In addition, the evolution laws of the dislocation length and interface morphology as well as the shear strain distribution are discussed.

Air and O2-Assisted Catalytic VACNT Growth Optimization for Uniformity and Throughput

The development of an optimized air or O2-assisted multi-wall vertically aligned carbon nanotubes (VACNT) process that adjusts the vertical height profile of a standard H2O vapor-assisted VACNT process is reported. The effect of the air or O2 chemical vapor deposition (CVD) precursor flow rate, the catalytic Fe layer thickness, the process growth temperature, and the H2/C2H4 ratio on VACNT length was first investigated to find the optimum growth conditions. Spatial distribution height mapping of VACNT structures on six patterned 4′′ catalyst Si wafers prepared with a 70–90 min long O2-assisted growth step shows an average growth height of 1.8–2.2 mm, with a standard deviation of less than 10%. Characterization techniques included Raman spectroscopy, scanning electron microscopy (SEM), and spatial height mapping analysis for a range of Fluid channel Array Brick (FAB) components with a length of 30 mm, a width range of 2.5–15 mm, a fluid channel diameter range of d = 5–100 mm, and a fluid channel closest gap range of g = 5–50 mm. A significant finding is that the O2-assisted VACNT growth process optimization efforts enable 2 mm parts processing with square edges, flat top surfaces, uniform height tolerances, and maximum catalyst wafer utilization for application in engineering devices.

Maximum energy product of exchange-coupled Sm(FeCo)12/α-Fe nanocomposite particle

The effects of the coating surface orientation of the α-Fe soft magnetic layer on the Sm(Fe0.8Co0.2)12 hard magnetic phase and the volume fraction of α-Fe, VFe, on the maximum energy product, (BH)max of exchange-coupled Sm(Fe0.8Co0.2)12/α-Fe nanocomposite magnet particles were micromagnetics OOMMF package was systematically investigated. The (BH)max of the reference model, Sm(Fe0.8Co0.2)12 particles without Fe layer, was 630 kJ/m3. In contrast, in the nanocomposite magnet particle model with soft magnetic layers on both sides of the hard magnetic phase, (BH)max reached a maximum value of 657 kJ/m3 at VFe = 12% (Fe layer thickness, tFe = 2 nm). In the model with α-Fe coating on the top and bottom surfaces of the hard magnetic phase, (BH)max = 636 kJ/m3 at VFe = 4% (tFe = 2 nm). Furthermore, the coating of the soft magnetic phase on both sides of the hard phase particles reduces the magnitude of the demagnetizing field, Hd of the nanocomposite magnet particles, indicating that the side coating of the soft magnetic phase is effective in increasing (BH)max. These findings allow for a greater degree of freedom in the design of nanocomposite magnets by adjusting not only the VFe volume fraction of the hard/soft phases but also their arrangement.

Electronic energy transport in nanoscale Au/Fe hetero-structures in the perspective of ultrafast lattice dynamics

We study the ultrafast electronic transport of energy in a photoexcited nanoscale Au/Fe hetero-structure by modeling the spatiotemporal profile of energy densities that drives transient strain, which we quantify by femtosecond x-ray diffraction. This flow of energy is relevant for intrinsic demagnetization and ultrafast spin transport. We measured lattice strain for different Fe layer thicknesses ranging from few atomic layers to several nanometers and modeled the spatiotemporal flow of energy densities. The combination of a high electron-phonon coupling coefficient and a large Sommerfeld constant in Fe is found to yield electronic transfer of nearly all energy from Au to Fe within the first hundreds of femtoseconds.

Perpendicular Magnetic Anisotropy and Its Electric Field Manipulation in Magnetic Multilayered Heterostructures

"Understanding of underlying physics related to the Perpendicular Magnetic Anisotropy (PMA) in magnetic heterostructures represents a major issue for its exploit in random-access memory (MRAM) devices. Using ab-initio analysis, we reveal some basic aspects related to the anatomy of PMA and its variation with electric field in various X/Fe/MgO(001) multilayer configurations (X=Cr, Au, V, Ag, Pt, Pd,…) compatible with standard experimental architectures of magnetic tunnel junction devices. Our study quantifies and underlines the significant role of the Rashba interfacial field on PMA. We explain and correlate the sign, the magnitude, and the electric field dependence of the PMA, the Rashba coefficient R and the Dzyaloshinskii–Moriya (DMI) asymmetric exchange interaction parameter. Moreover, when varying the Fe thickness in X/Fe/MgO(001) systems, we observe oscillations of PMA with the number of Fe monolayers, explained within the framework of quantum wells of the 1 Bloch symmetry electrons in Fe. Further atomistic micromagnetic simulations including different Fe layer thicknesses and the corresponding PMA predict macroscopic magnetization characteristics in realistic experimental systems. Keywords: perpendicular magnetic anisotropy, electric field control of PMA, magnetic tunnel junctions, magnetic multilayer heterostructures, atomistic magnetic simulations. "

Hot carrier effect in Ferro-FinFET for variation in temperature, work function, and FE layer thickness

Using 3D TCAD simulator, the hot carrier effects (HCEs) in terms of impact ionization rate and horizontal electric field are reported for Ferro-FinFET taking temperature, work function of gate (ɸM), and ferroelectric thickness (tFE) as parameters. It is observed, these parameters have significant impact on the HCEs of Ferro-FinFET. It is perceived from analysis that temperature, ɸM, and tFE have observable impact on DC characteristics and a hysteresis loop is formed between forward and reverse sweep. We have shown the impact of temperature, ɸM, and tFE on the subthreshold swing (SS) and the ION/IOFF of Ferro-FinFET.

Small signal model and analog performance analysis of negative capacitance FETs

In this paper, a small-signal model of Negative Capacitance FETs (NCFETs) is developed and the analog performance of NCFETs is studied using the developed model. A new ferroelectric factor K is introduced to capture the ferroelectric gain in NCFETs as compared to traditional small signal MOSFET/FinFET models. Using our new NCFET small-signal model, we show analog design trade-offs between various analog benchmarks such as gain, bandwidth, cut-off frequency, and linearity. Additionally, the developed model is used to demonstrate trade-offs in NCFET analog performance as ferroelectric parameters are changed. Results show that if pushed for a higher intrinsic gain via thicker Fe layers in NCFETs, the linearity of the device suffers. This reveals inherent device level trade-off in NCFETs for analog circuit performance.

Peculiarities of Magnetoresistance of [Fe/SiO]n Discontinuous Multilayers

The influence of the magnetic and insulator layer thickness on the crystal structure and magnetoresistive properties of [Fe/SiO]n discontinuous multilayers has been studied. The results indicate that the decreasing of Fe layer thickness within the range from 10 to 3 nm leads to the transition of microstructure of the samples from nanocrystalline to amorphous. For all investigated systems in an as-deposited state, the isotropic nature of the field dependences of magnetoresistance is observed. For samples with layer thickness dFe = 4–6 nm and dSiO = 5 nm, the transition to isotropic MR occurs after annealing to 400 K. However, for samples with Fe layer thickness of 7–10 nm, such transition is not observed regardless of the effective thickness of insulator layer and annealing temperature.

Magnetization and Magnetic Microscopy Studies in Fe Thin Films

This paper reports the magnetic domain imaging and magnetization studies carried out on Fe thin films grown with different thicknesses, namely, 5, 15 nm, 30 nm, 50 nm, 75 nm and 100 nm. Films were grown on Si at two different substrate temperatures, namely, room temperature and 550°C. Based on the detailed studies carried out, it was observed that Fe layer thickness and substrate temperature are important control parameters in tuning the magnetic anisotropy along the in-plane (IP) or out-of-plane (OOP) directions. A crossover from surface to volume anisotropy has been demonstrated with change in film thicknesses. Domain imaging studies carried out on Fe films grown at different substrate temperatures and with different thicknesses aided us to understand the magnetic anisotropy and magnetization reversal mechanisms.

Thickness dependence of spin torque effect in Fe/MgO/Fe magnetic tunnel junction: Implementation of divide-and-conquer with first-principles calculation

In this study, we develop a divide-and-conquer (DC) method under the framework of first-principles calculation to prevent directly solving Hamiltonian of a large device with time-consuming self-consistent process. The DC implementation combined with JunPy package reveals the oscillatory decay of layer-resolved spin torques away from the MgO/Fe interface, and suggests a very thin Fe layer thickness below 2 nm to preserve the efficient current-driven magnetization switch. This newly developed JunPy-DC calculation may efficiently resolve current self-consistent difficulties in noncollinear spin torque effects for novel spintronic applications with complex magnetic heterostructures.

The first and the second-order magnetic anisotropy in a Fe/MgO system under electric field: a first-principles study

We studied the first- and the second-order magnetic anisotropy coefficients, K 1 and K 2, of Fe atomic monolayers on a MgO(001) substrate under an electric field by using first-principles calculations. Special attention has been paid to the effect of the Fe layer thickness and the Cr-capping layer on the electric field dependence of K 1 and K 2. The results show that for all the systems we studied the electric field derivatives of K 1 and K 2 have the opposite sign to each other as observed in recent experiments.

Monte Carlo simulation study of reflection electron energy loss spectroscopy of an Fe/Si overlayer sample

Reflection electron energy loss spectroscopy (REELS) has been used to study the optical and electronic properties of semi‐infinite solid samples, aided by a theoretical model of the interaction between electrons and a solid. However, REELS has not been used to its full capacity in studying nanomaterial samples because of the difficulty in modeling the electron interaction with a layered nanostructure. In this study, we present a numerical calculation result on the spatially varying inelastic mean free path for a sample comprising an Fe layer of varying thickness on an Si substrate. Furthermore, a Monte Carlo model for electron interaction with this Fe‐Si layered structure sample is built based on this inelastic scattering cross section and used to reproduce the REELS spectra of Fe‐Si layered structures. The simulated spectra of the sample with varying Fe layer thickness on top of a Si substrate were compared with the experimental spectra. This comparison clearly identifies that the Fe layer remaining on top of the experimental Si substrate after Ar+ beam sputtering is in the form of a homogeneous mixed layer, where the Fe/Si interface excitation is absent in the experimental spectra owing to pulverization of the Fe/Si interface during the Ar+ sputtering process.

Micro-structure and tribological behaviors of magnetron sputtered WS x /Fe/a-C/Fe multi-layer films with various Fe layer thicknesses

ABSTRACT The WS x /Fe/a-C/Fe multi-layer films with various Fe layer thicknesses were prepared by using magnetron sputtering and alternate deposition of WS x , Fe, and a-C layers on the silicon substrates. The morphology, micro-structure, and composition of the films were characterized by scanning electron microscope, energy dispersive spectroscopy, electron probe micro-analyzer, X-ray diffraction, and X-ray photoelectron spectroscopy. The mechanical and tribological properties of the fabricated films were evaluated by using nano-indenter, film stress tester, scratch tester, and ball-on-disk tribotester. According to the obtained results, all the multi-layer films revealed a featureless micro-structure with a smooth and dense surface. As the thickness of Fe layer increased, the S/W ratio of the films was decreased from 1.38 to 1.16, the hardness, elastic modulus, and adhesion of the films were gradually improved. Both the steady-state friction coefficient and wear rate were declined first and, then, enhanced. The film with the Fe-layer thickness of 4 nm exhibited the highest hardness (10.6 GPa) and adhesion (38.0 N); whereas, film with the Fe-layer thickness of 2 nm showed the best tribological performance with a steady-state friction coefficient of 0.218 and wear rate of 1.63 × 10−15m3 N−1 m−1.

Interface-related magnetic and vibrational properties in Fe/MgO heterostructures from nuclear resonant spectroscopy and first-principles calculations

We combine $^{57}$Fe M\"ossbauer spectroscopy and $^{57}$Fe nuclear resonant inelastic x-ray scattering (NRIXS) in nanoscale polycrystalline [bcc-$^{57}$Fe/MgO] multilayers with various Fe layer thicknesses and layer-resolved density-functional-theory (DFT) based first-principles calculations of a (001)-oriented [Fe(8 ML)/MgO(8 ML)](001) heterostructure to unravel the interface-related atomic vibrational properties of a multilayer system. In theory and experiment, we observe consistently enhanced hyperfine magnetic fields compared to bulk which are associated with the Fe/MgO interface layers. NRIXS and DFT both reveal a strong reduction of the longitudinal acoustic (LA) phonon peak in combination with an enhancement of the low-energy vibrational density of states (VDOS) suggesting that the presence of interfaces and the associated increase in the layer-resolved magnetic moments results in drastic changes in the Fe-partial VDOS. From the experimental and calculated VDOS, vibrational thermodynamic properties have been determined as a function of Fe thickness and are found to be in excellent agreement.