CoFe Layer Research Articles

A high magnetic energy product obtained in hot-deformed Nd-Fe-B magnet by chemical plating Fe-Co bilayer films

This study investigates a novel method, chemical plating, with the goal of integrating nano-sized ferromagnetic materials into hot-deformed Nd-Fe-B magnets, potentially enhancing their magnetic properties. Coating Fe-Co double layers on Nd-Fe-B magnetic powder resulted in a significant improvement in the remanence over 10 %, increasing from 1.37 to 1.45 T, as well as an increase in the maximum magnetic energy product from 45.95 to 52.02 MGOe in hot-deformed Nd-Fe-B magnets. Microstructure observations revealed that the coarse non-oriented grains at the interface of powder ribbons were suppressed and the texture of grain alignment in the interior of powder ribbons was enhanced after the coating of Fe-Co. Additionally, there was a noticeable increase in the concentrations of ferromagnetic elements in intergranular phases. The reduced coarse grain regions, the enhanced grain alignment and the increased ferromagnetic intergranular phases are considered to be the main reasons for the enhancement of remanence and maximum magnetic energy product in hot-deformed magnets.

Silk Fibroin Film Decorated with Ultralow FeCo Content by Sputtering Deposition Results in a Flexible and Robust Biomaterial for Magnetic Actuation.

Magnetically responsive soft biomaterials are at the forefront of bioengineering and biorobotics. We have created a magnetic hybrid material by coupling silk fibroin─i.e., a natural biopolymer with an optimal combination of biocompatibility and mechanical robustness─with the FeCo alloy, the ferromagnetic material with the highest saturation magnetization. The material is in the form of a 6 μm-thick silk fibroin film, coated with a FeCo layer (nominal thickness: 10 nm) grown by magnetron sputtering deposition. The sputtering deposition technique is versatile and eco-friendly and proves effective for growing the magnetic layer on the biopolymer substrate, also allowing one to select the area to be decorated. The hybrid material is biocompatible, lightweight, flexible, robust, and water-resistant. Electrical, structural, mechanical, and magnetic characterization of the material, both as-prepared and after being soaked in water, have provided information on the adhesion between the silk fibroin substrate and the FeCo layer and on the state of internal mechanical stresses. The hybrid film exhibits a high magnetic bending response under a magnetic field gradient, thanks to an ultralow fraction of the FeCo component (less than 0.1 vol %, i.e., well below 1 wt %). This reduces the risk of adverse health effects and makes the material suitable for bioactuation applications.

Mitigation of Gilbert Damping in the CoFe/CuOx Orbital Torque System.

Charge-spin interconversion processes underpin the generation of spin-orbit torques in magnetic/nonmagnetic bilayers. However, efficient sources of spin currents such as 5d metals are also efficient spin sinks, resulting in a large increase of magnetic damping. Here we show that a partially oxidized 3d metal can generate a strong orbital torque without a significant increase in damping. Measurements of the torque efficiency ξ and Gilbert damping α in CoFe/CuOx and CoFe/Pt indicate that ξ is comparable in the two systems. The increase in damping relative to a single CoFe layer is Δα < 0.002 in CoFe/CuOx and Δα ≈ 0.005-0.02 in CoFe/Pt, depending on CoFe thickness. We ascribe the nonreciprocal relationship between Δα and ξ in CoFe/CuOx to the small orbital-spin current ratio generated by magnetic resonance in CoFe and the lack of an efficient spin sink in CuOx. Our findings provide new perspectives on the efficient excitation of magnetization dynamics via the orbital torque.

Influence of the Substrate on the Exchange Coupling of NiO/FeCo Bilayers

Antiferromagnetic/ferromagnetic (AF/F) systems have been extensively investigated due to the importance that interfacial exchange coupling effects have in the development of magnetic storage technologies. Recently, these systems have garnered interest for the potential they have to imprint the magnetic moments of the AF into an F layer, offering the possibility of using it as a read-out mechanism in antiferromagnetic spintronics. In this study, we explored the importance of crystalline orientation and strains induced by the substrate in the exchange coupling properties of NiO/FeCo AF/F bilayers. For that, we have grown NiO/FeCo bilayers on MgO (001) and Al2O3 (0001) substrates varying the FeCo layer thickness. In addition, we have analyzed both deposited samples and those with induced interfacial unidirectional anisotropy. For inducing such interfacial anisotropy, we used a field cooling procedure, heating the bilayers to 650 K and subsequently cooling down to room temperature under the presence of an external magnetic field of 300 mT. We have investigated the effect of the substrate in terms of crystalline orientation and lattice mismatching on the AF/F exchange coupling as well as the dependence of the coercivity and exchange bias on the inverse F layer thickness that is consistent with the interfacial origin of the AF/F exchange coupling. Moreover, the angular dependence of the magnetic properties was explored by using vectorial Kerr magnetometry, confirming the presence of both magnetocrystalline anisotropy, arising from the epitaxial character of the growing process mainly when the bilayer is grown on MgO (001) substrates, and the field cooling (FC)-induced unidirectional anisotropy.

Epitaxy enhancement in oxide/tungsten heterostructures by harnessing the interface adhesion

The conditions whereby epitaxy is achieved are commonly believed to be mostly governed by misfit strain. We report on a systematic investigation of growth and interface structure of single crystalline tungsten thin films on two different metal oxide substrates, Al2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{3}$$\\end{document} (112¯0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$11\\bar{2}0$$\\end{document}) and MgO (001). We demonstrate that despite a significant mismatch, enhanced crystal quality is observed for tungsten grown on the sapphire substrates. This is promoted by stronger adhesion and chemical bonding with sapphire compared to magnesium oxide, along with the restructuring of the tungsten layers close to the interface. The latter is supported by ab initio calculations using density functional theory. Finally, we demonstrate the growth of magnetic heterostructures consisting of high-quality tungsten layers in combination with ferromagnetic CoFe layers, which are relevant for spintronic applications.

Second Harmonic Generation Versus Linear Magneto-Optical Response Studies of Laser-Induced Switching of Pinning Effects in Antiferromagnetic/Ferromagnetic Films

Composite magnetic nanostructures are a subject of high research interest, as they provide a number of exciting effects absent in live nature. Among others, much attention has been paid to the studies of exchange coupling in antiferromagnetic/ferromagnetic (AFM/FM) films, which leads to the pinning effect. It manifests itself as a widening and shift of the magnetic hysteresis loop with respect to zero value of the external magnetic field oriented along the pinning direction. In this work, we report on comparative studies of linear and nonlinear magneto-optical effects under the laser-induced switching of the pinning effect in IrMn/CoFe films of various thickness of the ferromagnetic CoFe layer. We found that the magneto-optical response of the pinned AFM/FM nanofilms appears with different hysteresis loop parameters in the transverse magneto-optical Kerr effect (MOKE) and interface-sensitive magnetization-induced second harmonic generation (SHG), indicating the diversity of the magnetic effects at interfaces compared to the bulk of the films.

First-principles study of the magnetic anisotropy of ultrathin B-, C-, and N-doped FeCo films

Iron-based layered systems are of great interest because of their ability to tune effective material parameters such as magnetic anisotropy energy (MAE). The influence of the crystallographic structure of Fe, its thickness, and the presence of other layers above and below the Fe layer on magnetic parameters, such as the MAE of the studied system, is an intriguing and important topic from an application point of view. Here, we present a density functional theory (DFT) study of the magnetic anisotropy of nine-monolayer Fe, FeCo, and FeCo films with B, C, and N dopants placed in octahedral interstitial positions. The theoretical study is based on calculations using the full-potential local-orbital code FPLO and the generalized gradient approximation. The chemical disorder in the FeCo layers was modeled using the virtual crystal approximation. The structures of the layers were subjected to optimization of the geometry of the interlayer spacings and the neighborhood of the dopant sites. We determined the local magnetic moments and the excess charge at each layer position. We also identified the influence of dopant atoms on the magnetic properties of FeCo layers, such as magnetization and magnetic anisotropy.

The Role of Ferromagnetic Layer Thickness and Substrate Material in Spintronic Emitters.

In this article, we investigate optically induced terahertz radiation in ferromagnetic FeCo layers of varying thickness on Si and SiO2 substrates. Efforts have been made to account for the influence of the substrate on the parameters of the THz radiation generated by the ferromagnetic FeCo film. The study reveals that the thickness of the ferromagnetic layer and the material of the substrate significantly affect the generation efficiency and spectral characteristics of the THz radiation. Our results also emphasize the importance of accounting for the reflection and transmission coefficients of the THz radiation when analyzing the generation process. The observed radiation features correlate with the magneto-dipole mechanism, triggered by the ultrafast demagnetization of the ferromagnetic material. This research contributes to a better understanding of THz radiation generation mechanisms in ferromagnetic films and may be useful for the further development of THz technology applications in the field of spintronics and other related areas. A key discovery of our study is the identification of a nonmonotonic relationship between the radiation amplitude and pump intensity for thin films on semiconductor substrates. This finding is particularly significant considering that thin films are predominantly used in spintronic emitters due to the characteristic absorption of THz radiation in metals.

Flexible Manipulation of Operating Range in Giant Magnetoresistance Unipolar Switch Based on Double-Pinned Spin Valve

Giant magnetoresistance (GMR) magnetic switches have been widely investigated due to their attractive advantages such as good stability, small size, large saturation field, and high integration. However, in currently available commercial GMR unipolar switches, the operation and release points are limited to a narrow range. In this work, a modified double pinned spin valve (SV) structure is proposed to achieve a wide operating range and easy modulation of magnetic unipolar switches. In particular, a modified SV structure of Ta/NiFe/IrMn/CoFe/Ru/CoFe/Cu/CoFe/IrMn/Ta was chosen, where the large and small exchange bias fields were obtained from the bottom synthetic antiferromagnetic (SAF) structure and the top CoFe/IrMn layers, respectively. Accordingly, the operating range can be easily modulated by adjusting the thickness of top pinned CoFe layer. It is worthwhile to note that the controllable range exceeds 100Oe, which is much larger than that exhibited by current commercialized SV structure. Furthermore, in the patterned sample having the modified double pinned SV, the operation and release points are independent of length and width. The reason is attributed to the exchange bias field, which weakens the impact of shape anisotropy. In addition, this result also facilitates the simplification of the design process. That is to say, the proposed modified double pinned SV offers a broad application region for GMR magnetic unipolar switches and reveals a new paradigm for the development of next-generation magnetic sensors.

631% room temperature tunnel magnetoresistance with large oscillation effect in CoFe/MgO/CoFe(001) junctions

We demonstrate tunnel magnetoresistance (TMR) ratios of up to 631% at room temperature (RT) using CoFe/MgO/CoFe(001) epitaxial magnetic tunnel junctions (MTJs). The TMR ratio increased up to 1143% at 10 K. The large TMR ratios resulted from fine-tuning of atomic-scale structures of the MTJs, such as crystallographic orientations and MgO interface oxidation by interface insertion of ultrathin CoFe and Mg layers, which are expected to enhance the well-known Δ1 coherent tunneling transport. Interestingly, the TMR oscillation effect, which is not covered by the standard coherent tunneling theory, also became significant. A 0.32-nm period TMR oscillation with increasing MgO thickness dominates the transport in a wide range of MgO thicknesses; the peak-to-valley difference of the TMR oscillation exceeds 140% at RT, which is attributed to the appearance of large oscillatory components in the resistance area product.

Magnetic properties of FeGa/FeCo bilayer

In this work, we investigated a series of polycrystalline FeGa/FeCo bilayers with different FeGa thicknesses fabricated by radio-frequency magnetron sputtering. The bilayers exhibit an in-plane anisotropy since an external magnetic field is applied in the plane of bilayers when FeGa layer is deposited. The grain size and the total saturation magnetization (4πMS) of FeGa/FeCo bilayers change with the increase of the thickness of the FeGa layer. In addition, the in plane and out-of-plane angle variation of resonance spectra are obtained by electron spin resonance measurement, indicating that the magnetic resonance field and the saturation magnetization of the FeGa and FeCo layer can be affected by the thickness of the FeGa layer respectively.

First-principles study of origin of perpendicular magnetic anisotropy in MgO|CoFeB|Ta structures

Using fist-principles calculations, we study the B atom of diffusion process and the origin of the perpendicular magnetic anisotropy in MgO|CoFe|Ta structures with boron. It is found that B atoms are more likely to enter the Ta layer than FeCo layer and MgO layer. This result is in good agreement with that of the experimental and theoretical results. Furthermore, we elucidate the physical origin of the interfacial PMA Ta|CoFe|MgO structure with B element. We find that interfacial PAM come from both the MgO|CoFe and CoFe|Ta layer interfaces. These findings provide a comprehensive understanding of the PMA and point towards the possibility to achieve the advanced-node STT-MRAM with high thermal stability.

Magnetocaloric Effect in CoFe-Electroplated Ni50Mn33In16Cr1 Alloy

A high-saturation magnetization CoFe layer was electroplated onto Ni50Mn33In16Cr1 alloy using a magnetic field assistance electroplating bath. This CoFe-coated alloy can function as an active magnetic regenerator owing to its magnetocaloric effect. The CoFe coating layer did not affect the entropy change calculated from the isothermal magnetization of the alloy, but it significantly affected the temperature variation of the alloy by changing the externally applied magnetic field. The temperature change of the CoFe-coated alloy increases with increasing CoFe coating times. By comparing with the as-sintered alloy, a maximum increase of 150% in temperature change can be observed in the alloy coated with CoFe for 2 h.

Preparation of Flower-Shaped Co-Fe Layer Double Hydroxide Nanosheets Loaded with Pt Nanoparticles by Corrosion Engineering for Efficient Electrocatalytic Water Splitting

Preparation of Flower-Shaped Co-Fe Layer Double Hydroxide Nanosheets Loaded with Pt Nanoparticles by Corrosion Engineering for Efficient Electrocatalytic Water Splitting

Influence of FeCo layer thickness on the interfacial asymmetry of FeCo/Si multilayers fabricated by direct current magnetron sputtering.

FeCo/Si is a promising material combination for polarized neutron supermirrors because of its appropriate optical constants. Five FeCo/Si multilayers with monotonically increasing FeCo layer thicknesses were fabricated. Grazing incidence x-ray reflectometry and high-resolution transmission electron microscopy were performed to characterize the interdiffusion and asymmetry of the interfaces. Selected area electron diffraction was used to determine the crystalline states of FeCo layers. It was found that the asymmetric interface diffusion layers existed in FeCo/Si multilayers. Furthermore, the FeCo layer started the transition from amorphous to crystalline when the thickness of the FeCo layer reached 4.0nm.

Magnetostrictive and Electroconductive Stress‐Sensitive Functional Spider Silk

AbstractElectronics and soft robotics demand the development of a new generation of hybrid materials featuring novel properties. Among these, remarkable mechanical properties are required to sustain mechanical stresses, and electrical and magnetic properties are essential to design the devices’ interface. In this study, a hybrid material is presented, consisting of a spider silk thread, providing mechanical robustness, coated with a layer of a magnetostrictive FeCo alloy, which ensures both electrical conductivity and stress‐sensitive magnetic properties. The durability and the homogeneity of the composite are validated, as well as its ability to respond to magnetic and mechanical stimuli. Despite the coating, the soft nature of the silk and its mechanical performances are preserved. The magnetic study reveals that the magnetic behavior of the film is strongly affected by the silk thread–FeCo layer interaction, especially under mechanical stresses. Indeed, when the composite is subjected to tensile strain, the magnetic signal changes accordingly, indicating that the layer–silk interaction is maintained and can be exploited to reveal the tensional state of the sample even under severe cycles. Therefore, the presented hybrid material is a flexible fiber with properties that are suitable for magneto‐electronics applications, e.g., magnetic actuators as well as strain/stress sensors.

In-situ investigation of exchange bias property in FePt (L10)/FeCo bilayer with increasing FeCo thickness

Magnetization reversal of soft ferromagnetic (FM) FeCo layer coupled to hard FM FePt (L10) layer in FePt (L10)/FeCo) bilayer has been studied in-situ with increasing thickness of FeCo layer. During FePt(L10) phase formation, an in-plane magnetic saturation field (HMAX) is applied to keep the hard FePt(L10) layer in its remanent state. Magneto-optical Kerr effect measurements reveal the absence of hysteresis loops initially up to 4.8 nm thickness of FeCo layer while loops with significant shift, i.e. exchange bias (EB) opposite to the HMAX direction, were observed on further deposition. The EB is found to decrease with the increasing thickness of the FeCo layer. It is due to the combined effect of both magnetostatic coupling and interfacial exchange interaction, where the contribution of magnetostatic interaction to EB is almost constant, and interfacial exchange coupling exhibits an inverse relation. Furthermore, different nucleation mechanisms during magnetization reversal in the descending and ascending branches of hysteresis loops lead to asymmetry in magnetization reversal at the lower thickness of the FeCo layer. This asymmetry decreases with the decrease in the interfacial coupling as the thickness increases. Azimuthal angle dependence of exchange shift with respect to the direction of HMAX further revealed the unidirectional character of the EB.

Interfacial magnetic vortex formation in exchange-coupled hard-soft magnetic bilayers

The exchange coupling between a hard magnetic layer MnBi and a soft magnetic layer Co-Fe has been found to significantly improve the maximum energy product. In this work, the spin structure of exchange-coupled MnBi:Co-Fe bilayers is experimentally investigated by X-ray magnetic circular dichroism (XMCD) and polarized neutron reflectometry (PNR). We find that the out-of-plane magnetization reversal process of the MnBi:Co-Fe bilayer structure involves formation of a curling-type twisting of the magnetization in the film plane at low or intermediate reversal fields. Micromagnetic simulations are further performed to provide a detailed view of the spins at the curling center. Reminiscent of chiral spin structures known as spin bobbers, this curling in the exchange-coupled hard-soft magnetic bilayers is a new type of skyrmionic spin structure and worth further investigation.

Enhanced performance and recyclability for peroxymonosulfate activation via g-C3N4 supported CoFe layer double oxide

CoFe layered double oxide (CoFe LDO) anchored on g-C3N4 was prepared by mixing appropriate amounts of CoFe layer double hydroxide and melamine at moderate synthesis temperatures. The resulting CoFe LDO/g-C3N4 composite has superior properties in peroxymonosulfate (PMS) activation, resulting in remarkable activity in catalyzing paracetamol degradation. It has been able to degrade 10 mg/L paracetamol in less than 10 min in darkness by using 0.2 g/L catalyst and 0.5 mM PMS dosages. The effects of PMS and catalyst dosage, initial pH and coexisting anions were also investigated. Negligible cation leaching, enhanced reusability and enhanced stability make CoFe LDO/g-C3N4 an attractive compound for environmental pollution abatement. The influence of g-C3N4 on lowering Co and Fe valence states in CoFe LDO compounds by covalent stimulates the oxidant radical (SO4− and OH) production and concomitantly paracetamol degradation. Electro magnetic resonance experiments and a so-called chemical probe were used to identify SO4− as the dominant radical in the degradation processes. Interestingly, X-ray absorption spectroscopy and electrochemical measurements revealed the existence of a second contributing mechanism, based on a pure electron transfer process from the pollutant to PMS mediated by the catalyzer. These findings, pioneer a new method for the mechanism of coupling radical and electron transfer processes that act synergistically to promote paracetamol degradation in scarcely 10 min in darkness.

Nd2Fe14B/FeCo Core–Shell Nanoparticle Synthesis Using Galvanic Substitution Based Electroless Plating

Core–shell structured magnetic nanoparticles combine hard and soft phases to improve energy efficiency. The mutual interaction of the two phases can lead to the exchange spring effect, leading to higher magnetic energy. In this regard, synthesis of Nd2Fe14B-based core–shell-structured powders have proven to be elusive, due to the relatively reactive nature of this phase. In this study, a process has been established for successfully coating the surface of Nd2Fe14B powders with a FeCo layer using the galvanic displacement method. Initially, a binary phase magnetic powder was synthesized containing Nd2Fe14B and Nd2Fe17 phase. Subsequently, the powders were coated using a Co precursor at 303 K. During coating, the metastable Nd2Fe17 phase was dissolved, and the Fe ions were released into the solution. Subsequently, the Fe ions deposited together with the Co ions on the surface of Nd2Fe14B powder to form a FeCo shell. The deposited layer thickness and composition was confirmed using TEM analysis.