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PHYSICO-CHEMICAL PROPERTIES OF AMORPHOUS COBALT-BASED ALLOYS: A REVIEW
... В більшості аморфних металічних сплавів дійсно існує ближній порядок, тобто порядок розміщення ближчих сусідів атомів, але відсутній дальній порядок. Наслідками такої аморфної структури виступають незвичайні магнітні, механічні, електричні властивості та корозійна тривкість (Badawy et al., 2000;Hasegawa, 2004;Ackland et al., 2018;Burkov & Chigrin, 2018;Louzguine-Luzgin et al., 2018;Vasić et al., 2018;Zhao et al., 2019;Boichyshyn et al., 2020;Liao et al., 2021;Lopachak & Boichyshyb, 2023;Nykyruy et al., 2023). Ці матеріали проявляють високу механічну твердість та міцність при розтязі, в ряді випадків мають близький до нуля коефіцієнт теплового розширення. ...
... Аморфні метали і сплави повинні бути дуже тривкими до корозії за рахунок хімічної однорідності. Багаточисельні дослідження (Badawy et al., 2000;Ackland et al., 2018;Burkov & Chigrin, 2018;Vasić et al., 2018;Boichyshyn et al., 2020;Lopachak & Boichyshyb, 2023) показали, що аморфні сплави на основі Co, які містять Cr і P, володіють дуже високою корозійною тривкістю в різних агресивних середовищах. Вони також, практично, не піддаються піттинговій корозії, навіть при анодній поляризації в розчинах натрій хлориду. ...
Corrosion resistance of ribbon amorphous alloys based on cobalt in acetic acid solutions of different concentrations was investigated by various physicochemical methods. An increase in corrosion resistance with an increase in acid concentration due to the formation of dense passivation layers on the surfaces was established. Most amorphous cobalt-based alloys are characterized by high strength and impact toughness, corrosion resistance, and high magnetic permeability. Amorphous metal alloys (AMА) based on Co, which are characterized by unique physicochemical properties, are used in the medical field, in particular, to create dental and bone implants. The study of their corrosion resistance in aggressive environments of organic acids makes it possible to choose amorphous alloys that will be more effective in this field. A potentiometric study of changes in the corrosion resistance of AMА Co73,2Fe4,8Si5,3B16,7 in aqueous solutions of acetic acid of different concentrations showed a higher durability of the alloy of this composition in acid solutions, compared to the sodium chloride solution, which is a standard for corrosion assessment. High durability is also confirmed by a small difference between the initial and final potential values. With an increase in acid concentration, the final potential values slightly shift to the anodic side, which reflects an increase in corrosion resistance. Similar potentiometric studies of AMА Co73,2Fe4,3Mn0,5Si5,3B16,7, which contains Mn, in aqueous solutions of acetic acid also confirmed the increase in durability with increasing acid concentration, which is obviously related to the formation of dense passivation layers under such conditions. The study of the corrosion resistance of AMА in aqueous solutions of acetic acid by the method of cyclic voltammetry, i.e. with additional loading of samples by cyclic scanning of the potential, showed that with an increase in the duration of contact with an aggressive environment under these conditions, a shift in the values of the corrosion potentials of both contact and external surfaces in the cathodic direction is observed and the growth of corrosion currents, which indicates a decrease in the corrosion durability of the samples. The contact surface is also characterized by higher corrosion resistance under such conditions. As the concentration of acetic acid increases, the durability of the samples increases, even under conditions of cyclic polarization of the samples. Based on the electrochemical parameters, it was found that the corrosion resistance increased with increasing acid concentration, apparently due to the formation of dense passivation layers on the surfaces. Microphotographs of surfaces and their elemental composition after contact with (0.01–1.0) M aqueous solutions of acetic acid confirmed the high durability of alloys of this composition in such aggressive environments.
For applications such as spin accumulation sensors for next-generation hard disk drive read heads, and for fundamental research, it is desirable to increase the spin signal in metallic non-local spin valves, which are central devices in spintronics. To this end, here, we report on the integration of high-spin-polarization Co–Fe binary alloy ferromagnetic injectors and detectors in Al-based non-local spin valves. Room-temperature deposition on amorphous substrates from an alloy target is shown to generate smooth, polycrystalline (110-textured), solid-solution body-centered-cubic Co75Fe25 films, which we characterize by energy dispersive x-ray spectroscopy, x-ray diffraction, x-ray reflectivity, atomic force microscopy, and electronic transport. Simple integration into transparent-interface Al non-local spin valves is then shown to realize up to a factor of ∼5 enhancement of the spin signal relative to Co, with full quantitative analysis yielding strikingly temperature-independent current spin polarizations exceeding 60%. We make a detailed quantitative comparison of these values with prior literature, concluding that Co–Fe alloys present a remarkably facile route to higher spin polarization and spin signals in non-local spin valves, with minimal barrier to adoption.
These days, electric motor qualities and energy-saving problems are significant to our society. The critical component of these problems is related to magnetic materials. In this respect, here, we investigated the (FexCo1−x)72B19.2Si4.8Nb4 (0 ≤ x ≤ 1, at 0.1 intervals) ribbon alloys’ structural, thermal, and magnetic properties. Replacing Co with Fe turned out to increase saturation magnetization up to 127.7 emu/g and improve thermal stability. Additionally, we conducted heat treatment at 843, 893, and 943 K for 10 mins, and the annealing effect in the amorphous (FexCo1−x)72B19.2Si4.8Nb4 (0.4 ≤ x ≤ 0.9, at 0.1 intervals) ribbons on structural and magnetic properties are analyzed. The saturated magnetization (Ms) value has increased by about 20 to 30 emu/g by the heat treatment and tends to increase as the annealing temperature increases until the annealing temperature approaches 893 K. After annealing at 943 K for 10 mins, the highest saturation magnetization of 156.8 emu/g was achieved. In addition, all four samples show the same coercivity trend. The coercivity decreases when the initial heat treatment at 843 K is applied to the ribbons. However, after annealing at this high temperature, such as 893, 943 K, the Fe3B, and (Fe, Co)23B6 phases are also generated and cancel out the good soft magnetic properties of α-(Fe, Co) phase.
Cobalt Iron Yttrium (CoFeY) magnetic film was made using the sputtering technique in order to investigate the connection between the thickness and annealing procedures. The sample was amorphous as a result of an insufficient thermal driving force according to X-ray diffraction (XRD) examination. The maximum low-frequency alternate-current magnetic susceptibility (χac) values were raised in correlation with the increased thickness and annealing temperatures because the thickness effect and Y addition improved the spin exchange coupling. The best value for a 50 nm film at annealing 300 °C for χac was 0.20. Because electron carriers are less constrained in their conduction at thick film thickness and higher annealing temperatures, the electric resistivity and sheet resistance are lower. At a thickness of 40 nm, the film’s maximum surface energy during annealing at 300 °C was 28.7 mJ/mm². This study demonstrated the passage of photon signals through the film due to the thickness effect, which reduced transmittance. The best condition was found to be 50 nm with annealing at 300 °C in this investigation due to high χac, strong adhesion, and low resistivity, which can be used in magnetic fields.
The magnetic properties of the amorphous Co57Fe5Ni10Si11B17 alloy have been studied by a vibrating sample magnetometer. The temperature dependence of saturation magnetization was measured and the Curie point and crystallization onset temperature were determined as 560 K and 760 K respectively. The coercive force was obtained as 200 A/m and saturation magnetization - 65 Am2 /kg. The alloy was produced in the form of a ribbon thickness of 30 µm using the melt spinning method, and its internal amorphous structure was examined by the X-ray diffraction method. The crystallization behavior of the alloy was studied using series of isothermal annealing of the samples of the alloy at temperatures in the range of 723-1023 K for different exposures (up to 240 minutes) and nanocrystalline phases were detected by the X-ray diffraction analysis.
Seawater electrolysis is considered an attractive alternative to conventional freshwater electrolysis for hydrogen production due to the abundance of seawater in nature. For this reason, efficient electrocatalysts for hydrogen evolution reaction (HER) in alkaline seawater are highly desired. In this study, we report an amorphous Co−P alloy on nickel foam (Co−P/NF) that behaves as an efficient and stable HER electrocatalyst for alkaline seawater electrolysis. The Co−P/NF presents high catalytic performance for HER, requiring a low overpotential of 213 mV to drive a current density of 100 mA cm⁻² and a Tafel slope of 120.2 mV dec⁻¹ in alkaline seawater. Furthermore, it shows remarkable electrochemical and structural stability in alkaline seawater.
Magnetic properties of amorphous Co70Fe3Mn3.5Mo1.5Si11B11 and Co73Fe1Mn3Mo1Si13B9 alloys, manufactured in the form of ribbons by rapid cooling from the melt, were studied using vibrating sample magnetometer and thermo-magnetic methods. The Curie point (648 K and 683 K), coercive force (180 A/m and 40 A/m), and saturation magnetization (83 Am2/kg and 85 Am2/kg) were defined. The nanocrystallization process of the amorphous Co70Fe3Mo1.5Mn3.5Si11B11 and Co73Fe1Mo1Mn3Si13B9 alloys were studied by DTA, X-ray diffraction, and using the thermo-magnetic method in the high magnetic field 800 kA/m. The crystallization onset temperatures of the alloys were defined as about 787 K and 729 K, respectively. The effect of a magnetic field on the crystallization behavior, revealed in a notable crystallization onset temperature decrease, was observed. The structure evolution induced by the isothermal annealing at temperature 753 K was studied and the X-ray diffraction structure analyses revealed nanocrystallization with hcp-Co, fcc-Co, and Co3B phases. FESEM studies revealed a nanoscale and flower-like structure on the ribbon surface after annealing at 753 K.
Fe-based amorphous alloys have advantages of low iron loss and high effective permeability, which are widely used in sensors and actuators. Power efficiency is one of the most important indicators among power conversion applications. We compared the magnetomechancial power conversion factors of metallic glassy ribbons FeCoSiB (Vitrovac 7600) and FeSiB (Metglas 2605SA1). We investigated the crystallization process under different annealing temperatures and tested the magnetomechancial coupling factors (k) and quality factors (Q) by using resonant and anti-resonant methods. We found that the maximum coupling factor of the annealed Vitrovac ribbons was 23% and the figure of merits k²Q was 4–7; however, the maximum coupling factor of the annealed Metglas ribbons was 73% and the maximum value of k²Q was 16. We can observe that the Metglas 2605SA1 ribbons have higher values of the magnetomechanical power efficiency than those of the Vitrovac 7600 ribbons, which means they are better to be used in subsequent research regarding acoustically driven antennas.
The aim of this work is to investigate the effect of annealing and thickness on various physical properties in Co40Fe40Yb20 thin films. X-ray diffraction (XRD) was used to determine the amorphous structure of Co40Fe40Yb20 films. The maximum surface energy of 40 nm thin films at 300 °C is 34.54 mJ/mm². The transmittance and resistivity decreased significantly as annealing temperatures and thickness increased. At all conditions, the 10 nm film had the highest hardness. The average hardness decreased as thickness increased, as predicted by the Hall–Petch effect. The highest low-frequency alternative-current magnetic susceptibility (χac) value was discovered when the film was annealed at 200 °C with 50 nm, and the optimal resonance frequency (ƒres) was in the low frequency range, indicating that the film has good applicability in the low frequency range. At annealed 200 °C and 50 nm, the maximum saturation magnetization (Ms) was discovered. Thermal disturbance caused the Ms to decrease when the temperature was raised to 300 °C. The optimum process conditions determined in this study are 200 °C and 50 nm, with the highest Ms, χac, strong adhesion, and low resistivity, which are suitable for magnetic applications, based on magnetic properties and surface energy.
One-dimensional Co-B amorphous alloy nanowires (NWs) were prepared using surfactant as a template and were treated with plasma to study the effect of different treatment times on the essential physical and chemical properties of the catalyst. The study showed that plasma with a certain amount of strength will not change the morphology and amorphous structure of the NWs within the chosen treatment time. It could, however, modify the electronic structure and active sites of the catalyst surface, increase its specific surface area and H2 adsorption capacity, and also improve the selective hydrogenation performance of cinnamaldehyde. Most of all, plasma treatment could also play an important role in the reuse of catalysts. After several recycling reactions, plasma treatment on Co-B amorphous alloy NWs could regenerate their high catalytic activity. This work provides a novel method for preserving the high catalytic activity and stability of amorphous alloy nanomaterials, as well as for increasing their reusability.
Full use of experimental measurements obtained by the mean of the X-ray diffraction technique and the Rietveld refinement has been implemented to study the effects of the addition of Si on the microstructural evolution of the Fe–Co–Ni alloy prepared by using a planetary ball mill (Fritsch P7). For this purpose, the mixtures of powders prepared have the general formula Fe60-xCo25Ni15Six (x = 0, 5, 10, 20, and 30 at.%). The related structures and microstructures were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. Microstructural parameters were determined by the Rietveld fitting of the X-ray Diffraction patterns. The systematical discussions about microstructures, including morphology, phase structure, lattice parameter, crystallite size, and lattice strain, were carried out. It was found that for the sample without Si, the allotropic transition hcp-Co to fcc-Co was identified, while the presence of Si metalloid may stabilize the hcp-Co phase during milling. Several solid solutions as well as bcc-Fe(Co), bcc-Fe(Co, Ni,Si), and fcc-Ni(Si) were refined. As a consequence of the Si additions, intense refinement of the microstructure (D ~ 10 nm; ε = 1.25%) and an amorphous phase were obtained for 30%Si after 100 h milling, namely that the Si has segregated in the grain boundaries and may increase the structural hardening and brittleness of the particles. The resulting nanostructure state is related to the concept of dislocations.
In this study, Co19Cr18Fe22Mn21Ni20 HEA thin films have been obtained by the modernized method of three-electrode ion-plasma sputtering of mosaic targets consisting of pure metals. The structure, electrical resistance and magnetic properties of films were investigated. Single diffuse halo is observed on the XRD patterns of the as-deposited films, which confirms their amorphous structure. Some of the thin films, which were annealed at 900 K in a vacuum were identified to be oxidized by the small amount of oxygen in the work chamber. After the heat treatment, the Co19Cr18Fe22Mn21Ni20 films are transformed from an amorphous state into a crystallized FCC solid solution with the lattice parameter a = 0.3613 nm. Also, the cubic B2 phase of FeCo with a lattice parameter of 0.2857 nm is formed in the annealed films. As a result of oxidation processes, a dispersed phase of manganese oxide is also arising after annealing. Calculation of the activation energy of the beginning of phase transition was carried out by the generalized Kissinger method. The temperature dependencies of electrical resistivity of films were measured by the four-point technique upon continuously heating in the high vacuum. Both as-deposited and annealed films clearly reveal a typical ferromagnetic behavior. The as-deposited HEA film exhibits the soft magnetic properties while the annealed films can be attributed to hard magnetic materials.
In this study, a new toxic-free Ti40Zr10Co36Pd14 amorphous alloy with a critical casting size of 5 mm diameter and 20 mm long has been synthesised through copper-mold casting process. The Ti40Zr10Co36Pd14 bulk metallic glass (BMG) rod has further formed into thin films through the filtered cathodic vacuum arc (FCVA) deposition process. To assess the biocompatibility and the surface behaviour of the synthesised Ti40Zr10Co36Pd14 BMG, the metallic glass (MG) thin films are fabricated on the glass substrate and cultured using murine osteoblast cells (MC3T3-E1) and human osteoblast-like cells (SaOS-2). Various characterisation techniques has been utilised to evaluate the surface properties and the cultured cells behaviour of the deposited thin films. The synthesised Ti40Zr10Co36Pd14 composition shows good biocompatibility similar to the routinely used Ti-6Al-4V. The osteoblast cells proliferate very well on the Ti40Zr10Co36Pd14 MGs and exhibit similar levels of alkaline phosphatase enzymatic activity to those of the controls and the Ti-6Al-4V material. The MC3T3-E1 cells adhered and spread faster on the alumina particle blasted Ti40Zr10Co36Pd14 and Ti-6Al-4V surfaces with osteoblast-like shapes. These results suggest that Ti40Zr10Co36Pd14 BMG is biocompatible and could support osteoblast differentiation. Thus, the new alloy can be used as a candidate material for potential biomedical application.
Amorphous metals have unusual magnetic properties that arise due to the disordered atomic arrangement. We show that Co x (Al 70 Zr 30 ) 100− x (65 < x < 92 at. %) amorphous alloys have a distribution in the local magnetic coupling and ordering temperature, which can be explained by nanoscale composition variations. We use competing anisotropies induced by the substrate and an applied field during growth to probe the Co concentration distribution. Only regions with high enough Co concentration develop a magnetic anisotropy along the magnetic field during growth, whereas regions of low Co concentration have an anisotropy dictated by the substrate. A Gaussian distribution in the Co concentration of width 5.1 at. % is obtained from the variation in anisotropy. The results demonstrate the importance of composition variations for emergent magnetic properties and have far reaching implications for the properties of disordered materials in general.
The effect of covalent element addition on the magnetic and magnetocaloric properties of ferrimagnetic Gd60Co20Fe20 amorphous alloy was studied. Particularly, the co-doping of B and Si promoted the magnetocaloric performance (with a larger magnetic entropy change |ΔSM| at higher working temperature) of the initial Gd60Co20Fe20 amorphous alloy. This is possibly ascribed to the modified magnetic transition behavior. Additionally, the broadened magnetocaloric effect with |ΔSM| of 2.25 J kg⁻¹ K⁻¹ at 222.5 K under a magnetic field change of 0–2 T and high relative cooling power of 396.0 J kg⁻¹ were obtained for (Gd0.6Co0.2Fe0.2)95B2Si3. These properties reveal that the material could be a good candidate as a magnetic refrigerant suitable for active magnetic refrigerators.
Carbon Fibre Reinforced Polymer composite (CFRP) is widely used in the aerospace industry, but is prone to delamination, which is a major causes of failure. Structural Health Monitoring (SHM) systems need to be developed to determine the damage occurring within it. Our motivation is to design cost-effective new sensors and a data acquisition system for magnetostrictive structural health monitoring of aerospace composites using a simple RLC circuit. The developed system is tested on magnetostrictive FeSiB and CoSiB actuator ribbons using a bending rig. Our results show detectable sensitivity of inductors as low as 0.6 μH for a bending rig radii between 600 to 300 mm (equivalent to 0.8 to 1.7 mStrain), which show a strain sensitivity resolution of 0.01 μStrain (surface area: ~36 mm²). This value is at the detectability limit of our fabricated system. The best resolution (1.86 μStrain) was obtained from a 70-turn copper (~64 μH) wire inductor (surface area: ~400 mm²) that was paired with a FeSiB actuator.
Owing to their unique mechanical and functional properties, both amorphous and nanocrystalline alloys have attracted extensive research interest over the past decades. However, in spite of the tremendous efforts dedicated to both kinds of alloys, their engineering applications are still hindered today because some fundamental issues, such as low thermal stability and poor ductility, are yet to be solved. To overcome these issues, one recent strategy proposed is to combine both amorphous and nanocrystalline structures in a single alloy through the use of either an amorphous or a nanocrystalline alloy as a "template". On the one hand, the derived amorphousenanocrystalline alloys may inherit the unique properties from either the amorphous or the nanocrystalline "template", such as outstanding magnetic properties, extraordinary wear/corrosion resistance, and superior hardness and strength. On the other hand, these amorphousenanocrystalline alloys also exhibit enhanced thermal stability and ductility, which are difficult to achieve for either the amorphous or the nanocrystalline alloy template. In this review article, we would like to first discuss a number of experimental methods developed to fabricate amorphousenanocrystalline alloys, including partial crystallization in amorphous precursors, grain boundary amorphization, and physical vapor deposition. After that, we will give an overview of the mechanical and functional properties of the amorphousenanocrystalline alloys. Finally, we will have a discussion on the existing applications of the amorphousenanocrystalline alloys in various areas such as renewable and green energy, catalysis, and surface protection.
Abstract The hydrogen evolution reaction (HER) is a half-cell reaction in water electrolysis for producing hydrogen gas. In industrial water electrolysis, the HER is often conducted in alkaline media to achieve higher stability of the electrode materials. However, the kinetics of the HER in alkaline medium is slow relative to that in acid because of the low concentration of protons in the former. Under the latter conditions, the entire HER process will require additional effort to obtain protons by water dissociation near or on the catalyst surface. Heterostructured catalysts, with fascinating synergistic effects derived from their heterogeneous interfaces, can provide multiple functional sites for the overall reaction process. At present, the activity of the most active known heterostructured catalysts surpasses (platinum-based heterostructures) or approaches (noble-metal-free heterostructures) that of the commercial Pt/C catalyst under alkaline conditions, demonstrating an infusive potential to break through the bottlenecks. This review summarizes the most representative and recent heterostructured HER catalysts for alkaline medium. The basics and principles of the HER under alkaline conditions are first introduced, followed by a discussion of the latest advances in heterostructured catalysts with/without noble-metal-based heterostructures. Special focus is placed on approaches for enhancing the reaction rate by accelerating the Volmer step. This review aims to provide an overview of the current developments in alkaline HER catalysts, as well as the design principles for the future development of heterostructured nano- or micro-sized electrocatalysts.
Substituting Fe with Co in Fe-based alloys to adjust the composition and optimize properties is a hot topic. Amorphous Fe84-xCoxZr7B9 (x=0, 7, 14, 21, 28, 35, 42) ribbons were prepared and annealed at their first exothermic peak temperature. The crystallization and magnetic properties of the alloys can be divided into two regions. The first region corresponds to the Fe84-xCoxZr7B9 (x=0, 7, 14, 21) alloys, and the second region corresponds to the Fe84-xCoxZr7B9 (x=28, 35, 42) alloys. There are four exothermic peaks for Fe84-xCoxZr7B9 (x=0, 7, 14, 21) alloys, and there are three crystallization exothermic peaks for Fe84-xCoxZr7B9 (x=28, 35, 42) alloys during crystallization. Only a single phase precipitates from the amorphous matrix for all alloys after annealing. With the increase in Co content, the lattice constant first increases up to 21 at.% Co and then decreases. The crystallization volume fraction (Vcry) and the grain size (D) continue to decrease. When the Co content is 21 at.%, there is little change in Co concentration between the nanocrystal and the remaining amorphous matrix. When the Co content is 42 at.%, the Fe content in the remaining amorphous matrix is significantly less than that in the nanocrystal, and the Co content in the remaining amorphous matrix is slightly higher than that in the nanocrystal. The content of Fe in the nanocrystal is higher than that of Co in the nanocrystal. The specific saturation magnetization Ms of as-quenched alloys and annealed alloys increases sharply up to 28 at.% Co and then decreases with a further increase in the Co content. The Ms values of annealed alloys are greater than those of as-quenched alloys. The coercivity Hc values of annealed alloys are lower than those of as-quenched alloys. For Fe84-xCoxZr7B9 (x=0, 7, 14, 21) alloys, the higher the Co content, the higher the difference between the Hc values of as-quenched and annealed alloys. For Fe84-xCoxZr7B9 (x=28, 35, 42) alloys, the difference between the Hc values of as-quenched and annealed alloys is small.
Amorphous magnetic alloys with large perpendicular magnetic anisotropy (PMA) have emerged as a suitable material choice for spintronic memory and high-frequency non-reciprocal devices on-chip. Unlike ferromagnets, ferrimagnets offer faster switching...
Nano-sized crystalline-amorphous heterostructures display prominent catalytic activity toward multifarious electrochemical reactions, while no rational component selection strategy could be provided hitherto. Herein, an accurate tactic by introducing assortative strong-weak Ru-Co adsorptive atomic pair into the construction of hollow Ru-CoMoSx nanotube arrays is first proposed. Benefiting from the favorable charge density redistribution and adjusted d-band centers over the coupling strong-weak Ru- Co adsorption sites, balanced adsorption behaviors could be achieved upon potential active centers, thereby leading to the very low reaction energy barriers. Indeed, due to the anticipatory strong-weak Ru-Co adsorption pair, the as-constructed crystalline- amorphous Ru-CoMoSx heterointerface affords one of the best electrocatalytic activity toward oxygen evolution reaction (OER) in alkaline media to date, with an extremely low overpotential of 147 mV at the current density of 10 mA cm-2. Also, it exhibits an admirable Pt-like hydrogen evolution (HER) behavior (35 mV @ 10 mA cm-2). Thereout, its application prospect in practical multi-scenario water electrolysis, including freshwater/seawater electrolysis and integrated photovoltaics-hydrogen production system, is well demonstrated. This work provides instructive guidance for the rational design and in-depth structure-activity analysis of nano-sized crystalline- amorphous heterostructures.
The anomalous Nernst effect (ANE) is one of the most intriguing thermoelectric phenomena, which has attracted growing interest both for its underlying physics and potential applications. Typically, a large ANE response is observed in magnets with pronounced magnetizations or nontrivial Berry curvature. Here, we report a significant ANE signal in compensated ferrimagnetic Co x Gd 1- x amorphous films, which exhibit vanishingly small magnetization. In particular, we found that the polarity of ANE signal is dominated by the magnetization orientation of the transition metal Co sublattices, rather than the net magnetization of Co x Gd 1- x films. This observation is not expected from the conventional understandings of ANE but is analogous to the anomalous Hall effect in compensated ferrimagnets. The joint contribution from the Berry curvature and the scattering mechanisms near the Co-dominant Fermi surface could interpret the Co-dominant property of ANE. Our work may trigger a more comprehensive understanding of ANE and may be useful for building energy-harvesting devices by employing ANE in compensated ferrimagnets.
Amorphous ribbons of (Fe0.82Si0.04B0.13C0.01)100-xCox (x = 0, 5, 10, and 15) were prepared by the melt-spinning technique, and their microstructure and magnetic properties were investigated. It was observed that the saturation magnetic flux density (Bs) of the alloys could be efficiently increased from 1.64 to 1.78 T by Co addition. Particularly, the (Fe0.82Si0.04B0.13C0.01)95Co5 amorphous alloy with 5 at. % Co exhibited a high Bs of 1.73 T and a low coercivity (Hc) of 8.9 A/m, which implies a potential industrial application. The (Fe0.82Si0.04B0.13C0.01)90Co10 alloy developed a dual-phase microstructure composed of the bcc-Fe(Co) crystalline phase of size 54 nm that was nonuniformly embedded in the amorphous matrix and exhibited an approximately linear hysteresis loop after annealing at 380 ℃ for 20 min. Magnetic domain walls were observed to support the variation of soft magnetic properties with different annealing temperatures. It is demonstrated that the (Fe0.82Si0.04B0.13C0.01)90Co10 alloy can form a controllable amorphous/nanocrystalline dual-phase microstructure after appropriate heat treatment even without the nucleating elements such as Cu or Au.
Amorphous Co78Si8B14 alloy, as a new potential catalyst, has hardly been used in the degradation of organic pollutant activated by peroxymonosulfate (PMS). In the study, the degradation performance of Orange II aqueous solution by PMS activated by amorphous Co78Si8B14 alloy in a heterogeneous catalytic process was studied at ambient temperature. The effects of initial solution pH, amorphous Co78Si8B14 alloy dosage and PMS concentration on Orange II degradation were examined in batch experiments. The results show that decolorization was strongly influenced by initial solution pH, amorphous Co78Si8B14 alloy dosage, and PMS concentration. The decolorization rate increased with the increase in pH value from 3 to 6.45. In contrast, it decreased sharply when the pH value of the solution increased from 6.45 to 11. The decolorization rate increased as the amorphous Co78Si8B14 alloy dosage and PMS concentration increased. Finally, the potential mechanism of Orange II removal by amorphous Co78Si8B14 alloy/PMS system was proposed systematically by comparing with the Co2+/PMS system.
Zr–Co–Cu–Al based metallic glasses (MGs) are potential material for making surgical equipment due to their ultra-high strength. However, presence of elemental Al in these alloys is not desirable due to biotoxicity. To counter this problem the present study is undertaken to design metallic glass forming composition by replacing Al with Ti. Design strategy adopted is based on thermodynamic modelling by rationalizing the effect of chemical enthalpy and atomic mismatch entropy along with statistically controlled atomic arrangement through configurational entropy. The rapid solidification technique was used to synthesize MG in melt spun ribbon form. The structural nature and glass stability of the ribbon are confirmed by X-Ray diffraction, transmission electron microscopy and differential scanning calorimetry. Corrosion response of the MG is thoroughly investigated using potentiodynamic polarization and electrochemical impedance spectroscopy in a simulated body fluid (SBF) environment. The mechanical property of MG is evaluated using microindentation technique. Improvement in corrosion resistance is observed in all the SBF solutions along with in vitro biocompatibility study using MG-63 cell viability experiment.
Fe64Co16Zr10B10amorphous alloy prepared by a single roller melt spinning was annealed under isothermal treatment at temperatures ranging from 550 to 650°C in a vacuum. Phase evolution and magnetic characteristic of Fe64Co16Zr10B10amorphous alloy were investigated in detail by combining X-ray diffraction, transmission electron microscopy, scanning transmission electron microscopy/energy dispersive spectroscopy, and vibrating sample magnetometer. At 550°C, the metastable intermediate α-Mn type phase precipitates, as well as an α-Fe(Co) phase. At 575°C, only metastable α-Mn type phase is observed. Scanning transmission electron microscopy/energy dispersive spectroscopy indicates that the α-Mn type nanocrystals contain Fe, Co, and Zr. More Zr is at the interface between the nanocrystals and the amorphous matrix. There is little change in Co concentration among the remaining amorphous matrix, the nanocrystals, and the interface between the nanocrystals and the amorphous matrix. With a further increase in annealing temperature, the crystallization volume fraction of the α-Mn type phase decreases, and the crystallization volume fraction of the α-Fe(Co) phase increases accordingly. Coercivity of Fe64Co16Zr10B10alloy undergoes a sharp rise above 550°C and a sharp decline above 600°C.
In the present study, the liquidus temperature, mixing enthalpy, and atomic mismatch factor are used to predict and empirically evaluate the amorphisation capability of Co-Fe-B alloys fabricated by melt spinning. Based on this approach, five out of seven alloys have an amorphous structure, confirming the capability of the proposed model in predicting the alloy compositions with higher amorphisation ability in a ternary alloy system in the absence of any costly elements, such as Nb, Mo and Zr. X-ray diffraction, TEM and Mössbauer results show that the other two alloys exhibit different in-situ crystallisation behaviour. In one case, only the free-side crystallises, whereas the crystallisation occurs through the entire thickness of the ribbon in the other alloy. The lower amorphisation ability exhibited by these alloys in relation to the predictive parameters has been evaluated. Additionally, there is a strong correlation between amorphisation ability and crystallisation behaviour of alloys. Alloys, which crystallise through eutectic mode, are more likely to exhibit high amorphisation capability, whereas crystallisation via the primary mechanism can be the sign of lower amorphisation ability. The output of the alloy design process is five amorphous alloys compositions, among which one is magnetically ultra-soft, Hc = 2.9 A/m; a surface crystalline alloy, with a low coercivity and higher value of anisotropy field compared to amorphous samples; and a nanocrystalline sample with a very high saturation flux density, Bs = 1.57 T. The surface crystallisation can eliminate the need for inducing transverse anisotropy by magnetic annealing. Therefore, optimising the alloy composition through this method can be a universal strategy of composition design for the fabrication of alloys with excellent properties, to be utilised in both high-Bs and low-Hc applications.
Crystallization kinetics of rapidly quenched Fe-Sn-B alloys under non-isothermal conditions were studied using differential scanning calorimetry. Formation of crystalline phases was analyzed by X-ray diffraction. Nominal chemical compositions were Fe81Sn7B12, (Fe3Co1)81Sn7B12 and (Fe81Sn7B12)99Cu1. Alloys were prepared by planar flow casting in the form of ribbons approximately 20 µm thick and 6 mm wide. Mechanism of crystallization was studied under framework of the Johnson-Mehl-Avrami-Kolmogorov model. Alloys exhibit two stages of crystallization. Results show decrease in activation energy of the first stage of crystallization with addition of Cu and increase with addition of Co. Crystallization mechanism of the first stage of crystallization for Fe81Sn7B12 and (Fe81Sn7B12)99Cu1 alloy starts as growth with increasing nucleation rate and continues as growth with decreasing nucleation rate. Addition of Co changes mechanism of crystallization. Which in case of (Fe3Co1)81Sn7B12 alloy starts as a growth with increasing nucleation rate. Then changes to growth with decreasing nucleation rate. After which nucleation rate decreases to zero. Rest of crystallization stage is governed by growth of pre-existing nuclei. In the first stage of crystallization α-Fe phase with bcc structure crystallizes from amorphous matrix. In the second stage of crystallization the remaining amorphous matrix crystalizes into tetragonal Fe2B phase and hexagonal FeSn phase. After the first stage of crystallization, 50 % to 55 % volume of studied alloys were crystalized. Addition of Cu decreases crystalline size of α-Fe crystallites by 60 % and decreases concentration of Sn in α-Fe phase by 0.8 at. %. Addition of Co doesn't affect the size of α-Fe crystallites and decreases the concentration of Sn in α-Fe phase by 1.7 at. %.
X-ray diffraction indicated an amorphous state of all annealed films, indicating that boron in CoFeW films could refine grain size and low annealing temperatures did not induce sufficient thermal driving force to support grain growth. The saturation magnetization (Ms) and low-frequency alternate-current magnetic susceptibility (χac) increased with the increase in the thicknesses and annealing temperatures, indicating the thickness effect and magneto-nanocrystalline anisotropy. The highest Ms and χac values of Co40Fe40W10B10 films were estimated to be 1233 emu/cm³ and 2.8, at an annealing temperature of 350°C and thickness of 100 nm. Surface energy increased with the increase in thickness and annealing temperature. The highest surface energy of 100 nm thick Co40Fe40W10B10 film was 38.52 mJ/mm² at 350°C. The Co40Fe40W10B10 film had the highest transmittance when annealing temperature was 200°C and 10 nm, and its transmittance rate was 32.7%. The transmittance decreased with the increase in thickness and annealing temperatures, while a higher thickness may inhibit the transfer of photon signals through the film, causing a low transmittance. In this study, the optimal condition of magnetic and adhesive properties of Co40Fe40W10B10 film was found to be 100 nm with annealing at 350°C due to high Ms, large χac, and strong adhesion.
In this current research, the effect of Co addition on the microstructure and anti-corrosion properties of equiatomic AlNiZrY high-entropy metallic glass (abbreviated to HE-MG) ribbons were investigated. Also, the thermal stability and crystallization activation energy of these HE-MG ribbons have been studied. Ribbons of composition (Al1/4Ni1/4Zr1/4Y1/4)100-xCox (x= 0, 5, 8, 12) were synthesized via arc-melting method and melt-spinning technique. By increasing the content of Co, we found that the melt-spun equiatomic AlNiZrY and Co-containing AlNiZrY HE-MG ribbons could still remain amorphous state. The thermal stability of ribbons were conducted by means of a differential scanning calorimeter (DSC), which suggested that the thermal stability of four kinds of HE-MG ribbons is higher than common Al-Ni-based amorphous alloys. The maximum apparent activation energy of crystallization through thermodynamic analysis at different heating rates can reach ∼630 kJ/mol for (Al1/4Ni1/4Zr1/4Y1/4)92Co8 HE-MG ribbons. The microstructure characterization of each HE-MG ribbon before and after one-day corrosion immersion was done by scanning electron microscopy (SEM). In order to evaluate the microhardness and corrosion resistance of the as-received HE-MG ribbons with and without the addition of Co, the microhardness measurements and the electrochemical corrosion tests in 3.5 wt.% NaCl solution were carried out. The results revealed that the average microhardness value of HE-MG ribbons are all above 470 HV0.1, regardless of whether the ribbons immersed in corrosive media for one-day immersion or not. The corrosion current density of (Al1/4Ni1/4Zr1/4Y1/4)88Co12 HE-MG ribbons is around 0.46 μA/cm², which possesses the sterling anti-corrosion property and opens vital possibilities for the development of high-performance metal coatings under the condition of harsh marine environment.
First-principle molecular dynamics is employed to study the geometrical structure, electronic structure, and magnetic properties of Co80-xMnxB20 (x = 0, 2, 4, 6, 8, 10, 12 at.%) amorphous alloys. Results demonstrate that Mn atom locates at substituted positions of Co atoms, and cage structure with Mn as a center is mainly a twisted Icosahedral structure. Mn or Co atoms tend to lose electrons, and B atoms tend to gain electrons. The addition of Mn atoms increases the splitting of p band of B atoms. Variation of magnetic moment increases and then decreases with the increase of Mn content. Simulation results are in good agreement with experiments. Magnetic moment of Mn atoms in amorphous alloy exhibits ferromagnetic arrangement when x > 6 at.%. However, when x > 6 at.%, some antiferromagnetic arranged Mn atoms appear, and there is a competition between ferromagnetism and antiferromagnetism in the alloy, which makes magnetic moment of the amorphous alloy gradually decrease.
The development of high-performance magnetic field-sensitive materials is in urgent need for magnetic sensors. In this paper, the effect of magnetic field annealing on the soft magnetic properties, thermal stability and stress-induced giant magneto-impedance (GMI) effect of Co69Fe5.5Ni1Si14.5-xPxB10 (x = 0, 0.5, 1, 1.5, 2) amorphous alloys were investigated in detail. Thermal analysis shows that replacing Si with a small amount of P can increase the thermal stability of the amorphous alloys. The permeability of the samples with magnetic field annealing is about 150% higher than that of the samples with stress-relieve annealing. The stress-induced GMI (GSI) results show that when the applied tensile stress is 0 MPa, 100 MPa, and 300 MPa, the maximum GMI ratio of the 1 at. % P-doping alloy with magnetic field annealing first increases from 76.6% to 102.8% and then decreases to 82%. Under the optimized measurement conditions, the magnetic field response sensitivity ξ of the Co69Fe5.5Ni1Si13.5P1B10 ribbon reached to 35.3%/Oe, the GSI ratio reached 34.3%, which has significant improvement compared to that of the stress-relieve annealing samples. Therefore, the magnetic field annealing technique greatly improved the GSI effect of the Co-based amorphous alloys, and the results obtained show a new way to develop high-performance GSI sensor materials and can be used in the construction of stress sensors.
Nanoscale structural heterogeneity is a critical parameter for understanding the structure-property relationships in amorphous alloys. Herein, the small-angle X-ray scattering and atomic force microscopy were utilized to quantitatively investigate the nanoscale structural heterogeneity of the Fe80-xMxSi9B11 (M = Co and Ni; x = 0, 2, 4) amorphous alloys. The results show that the nanoscale structural heterogeneity of the amorphous alloys increases prominently with Ni substitution, but gradually decreases with the increase of Co content. Such evolution of structural heterogeneity was further verified by the changes in mechanical behavior. The microalloying of Ni can increase the plastic deformation ability and reduce the microhardness, whereas an opposite effect is found in the Co-doped alloys. Finally, Mössbauer spectroscopy reveals an enhancement in ferromagnetic exchange interaction and magnetic anisotropy with Co substitution, while the microalloying of Ni leads to a deteriorative result. Such variations in magnetic properties can be attributed to the evolution of nanoscale structural heterogeneity with Co and Ni additions. Our observation serves as a link between the nanoscale structural heterogeneity and magnetic properties, providing a new sight into understanding the structural origin of the changes in magnetic properties of Fe-based amorphous alloys.
For the development of rare-earth free permanent magnets with better performance to cost ratio, V and B dopings were employed to enhance the hard magnetic properties of Zr-Co-V-B alloys. The effect of V and B microalloying additions on the magnetic properties, phase stability and microstructure of the metastable Co5Zr phase have been investigated with experimental measurements together with first principles based on the DFT (density Functional Theory) calculations. This study also investigates the effects of annealing at different temperatures on the intrinsic and extrinsic magnetic properties of Co82Zr12V6-xBx melt-spun ribbons. Rapidly solidified Co82Zr12V6-xBx (x=1, 2, 3) alloy ribbons were produced by melt-spinning. For as-spun Co82Zr12V6-xBx (x=1, 2, 3) ribbons, the coercivity Hc decreases from 2.34 kOe to 0.008 kOe with increasing x value from 1 to 3. The amorphous alloy ribbons were annealed in a vacuum furnace at a series of temperatures of 600°C, 650°C, 700°C and 750°C each for 30 minutes. The XRD analysis showed presence of two soft magnetic phases (fcc-Co and Co23Zr6), accompanied with a hard phase Co5Zr in ribbons thus leading to the desired hard/soft structure and the amount of both (hard and soft) phases increased with the annealing temperature. Coercivity was found to increase upon annealing treatment. The phase stabilities of the Co82Zr12V6-xBx ribbons were calculated from the total energy by the DFT calculations in this work. The calculated magnetic anisotropy energies have been compared to that of experimental coercivity values. Annealed sample Co82Zr12V5B1 showed the maximum coercivity value of 3.58 kOe due to formation of high volume fraction of hard magnetic phase (Co5Zr) and evenly distributed finer grains throughout the matrix. However, annealing under the same conditions resulted in lower coercivity of about 0.088 kOe and 1.61 kOe for Co82Zr12V3B3 and Co82Zr12V4B2 samples, respectively. Although sample Co82Zr12V4B2 exhibited higher remanence (42.80 emu/g) and maximum magnetization value with the applied field of 17 kOe (i.e. M17= 77.70 emu/g) compared to Co82Zr12V3B3 sample.
In the present paper, the role of Co content on phase structure, thermal stability and anti-corrosion performance of melt-spun (Al1/3Ni1/3Y1/3)100-xCox (x= 5, 8, 12, 15 and 20 at.%) high entropy metallic glasses has been investigated. The microstructure and average hardness of AlNiYCox alloy ribbons were characterized and detected using a scanning electron microscope (SEM) and Vickers-type hardness tester, respectively. The corrosion behavior in 3.5 wt% NaCl solution was tested through the conventional potentiodynamic polarization curves (Tafel curves) and electrochemical impedance spectroscopy (EIS). Results suggested that all kinds of high entropy metallic glass ribbons could remain amorphous nature and the crystallization onset temperature are all above 750 K. The average hardness value of each ribbon sample is more than 530 HV0.1 as well. With the increase of Co content, the corrosion resistance begins to enhance and then lowers gradually. When the Co content increases from 5 at.% to 20 at.%, it can result in a decrease of corrosion current density from 9.546 µA/cm² of the (Al1/3Ni1/3Y1/3)95Co5 to 0.508 µA/cm² of the (Al1/3Ni1/3Y1/3)92Co8 and 0.741 µA/cm² of the (Al1/3Ni1/3Y1/3)80Co20 alloy ribbons. Therefore, it is assumed that adding appropriate content of Co element into (Al1/3Ni1/3Y1/3)100-xCox alloys can enhance ability to resist corrosion in 3.5 wt% NaCl solution. The ribbons with 8 at.% Co exhibited the excellent anti-corrosion performance in this current study.
Amorphous alloys exhibit excellent catalytic performance in the degradation of azo dye wastewater due to their unique atomic structure. Unfortunately, amorphous alloys with both high degradation efficiency and considerable reusability are still unsatisfactory for a long time. In this work, a new Co-Mo-B amorphous alloy wire reported can degrade the Direct Blue 6 (DB 6) solution within 2 min with a degradation efficiency of 99%. Importantly, the novel Co-based amorphous alloy also exhibits excellent reusability with 97% degradation efficiency after 20 cycles. The superior degradation performance and good long-term reactivity are mainly due to the synergistic coordination of Co and Mo bimetals and the self-exfoliation effect of the corrosion products. Such findings can provide a new idea for the development of amorphous alloys in the degradation of azo dye wastewater.
We study the corrosion resistance of an amorphous cobalt-based alloy (AMA) by the method of cyclic voltammetry (VA) in a 1 M KOH aqueous medium at different temperatures varying from 293 to 333°K. It is shown that, as a result of fivefold cyclic polarization of electrodes within the range from – 1.5 to + 0.5 V, the corrosion potential shifts to the cathodic side and, in solutions with temperatures of 313–333°K, takes almost identical values. The corrosion current density in AMA becomes eight times higher as the temperature of solution increases to 313°K. The corrosion resistance of AMA used in the reaction of hydrogen release becomes higher as follows from the values of current density that are twice lower than for the alloys in the intact state. The computed values of corrosion activation energy are equal to 18.65 and 17.86 kJ/mole for the first and fifth cycles of the VA curve, respectively. This corresponds to the diffusion-controlled interaction of hydroxyl ions with the surfaces of AMA electrodes. We computed the activation energy of formation of compounds on the AMA surface. It was established that the [Co–O–H2O]ads chemisorbed complex is formed with a twice higher activation energy than the passivating layers.
Herein, the crystallization behavior, thermal stability, phase composition, and magnetic properties of Co66.5Si15.5B12Fe4Ni2 amorphous alloy were determined via differential scanning calorimetry, X-ray diffraction analysis, and vibrating sample magnetometry. The heating rate was found to strongly affect the glass-transition and crystallization behavior of Co66.5Si15.5B12Fe4Ni2 solidified ribbon. Based on the crystallization behavior, the relationship between the glass-transition temperature (Tg) and the heating rate (lnβ) was derived as Tg = 6lnβ + 709 and the glass-transition activation energy, initial crystallization activation energy, first crystallization peak activation energy, and the second crystallization peak activation energy were also calculated. Based on the results, the nucleation mechanism of the crystallization of Co66.5Si15.5B12Fe4Ni2 amorphous alloy and the crystallization products of the annealing crystallization process were discussed. The phase composition after short-term annealing at a low temperature was found to be β-Co + α-Co + Ni3Fe + Ni4B + Ni2Si. Following high-temperature, long-term annealing, Ni2Si disappeared completely and a new phase, FeSi, was formed. By studying the coercivity, remanence, saturation magnetization, and magnetic anisotropy of the alloy, we obtained the best processing parameters for comprehensive soft magnetic properties. The results provide guidance on the development of new soft magnetic materials.
In this paper we present the conception of a temperature sensor based on a ferromagnetic microwire having a diameter of about 100 μ m and a composition of CoFeSiB as 80 % Co-Fe, 20 % Si, B. We experimentally analyze the influence of the temperature and excitation frequencies on the hysteresis loop of the material. Discussion about how the temperature can act as a measurand through the analysis of the output of the sensor is carried out. Temperature is correlated with the magnetic characteristic of the material, and the results are addressed in light of the recent literature and of the Ising model. All measurements were performed under controlled conditions. An ad-hoc setup was developed, and an experimental analysis was carried out to characterize the microwire temperature sensor.
The microstructures and soft magnetic properties of Co66Fe4Mo2Si16B12 amorphous tape wound core were systematically investigated. The phase composition and corresponding structure evaluation of Co66Fe4Mo2Si16B12 amorphous ribbon after annealing at various temperatures were identified firstly. In particular, at 758 K the microstructure of the ribbon is primarily composed of Co2B, Fe2B and β-Co phases. With the temperature approaching to 768 K, the new phases α-Co and CoSi appears. When the temperature increases to 778 K, the mixed phase combination of α(Co) + β(Co) + Co2B + Fe2B + CoSi exists along with an apparent nano-crystallization. The soft magnetic properties of tape wound core assembled by Co66Fe4Mo2Si16B12 amorphous ribbon were then studied at annealed temperature from 713 K to 753 K. At 723 K, we found the permeability is highest with a maximum value of μm = 1.675 × 10³, and the coercive force is lowest with a minimum value of 0.134 Oe. The magnetization curve and the hysteresis loop of established tape would core annealed at 713–753 K remain almost unchanged. Finally, the relation between frequency and magnetic permeability and quality factor were carefully examined at different annealing temperatures.
Metallic glasses (MGs), with their unique disordered atomic packing structure and superior catalytic capabilities, have gradually been realized with their significance in the field of catalysis. As a new type of promising catalyst, recent reports have demonstrated that MGs exhibit many excellent catalytic properties in wastewater treatment, such as ultrafast catalytic efficiency and reliable stability with a reduced metal leaching effect, etc. This review introduces, for the first time, recent developments in using MGs with various atomic components and excellent catalytic performance as environmental catalysts. In terms of the unique properties of MGs, this article provides a full discussion of several effects of their physical characteristics on catalytic reactivity, such as structural relaxation, crystallization, and rejuvenation, electronic structure, atomic configuration, thermophysical property, atomic composition, surface roughness, residual stress, and porosity by dealloying. The catalytic performance, including decolorization, mineralization, metal leaching, sustainability and reusability, as well as the effects of different chemical parameters, is systematically reviewed. This review also delivers several important prospects in further developing MG catalysts, offering new research opportunities into the study of their novel functional applications and providing new insights into the synthesis of novel catalysts.
The amorphous Co70Fe5Si10B15 alloy was studied in terms of thermal and corrosion resistance as well as thermally induced structural transformations, using several structural and thermal analysis techniques and electrochemical measurements. It was shown that the alloy is thermally stable up to around 510 °C. Anodic polarization curves of the as-prepared alloy revealed its high corrosion resistance in 0.5 M NaCl, HCl and NaOH solutions. Multistep structural stabilization through the crystallization is manifested as two well defined DSC peaks corresponding to formation of fcc Co, hcp Co, Co23B6, and Co2Si phases, whose microstructural parameters were studied after thermal treatment at different temperatures in the range 25–800 °C. TEM and EDX analyses suggested the presence of minor Co-Si phases as well in the crystallized alloy and deformation twinning in the Co23B6 grains. The microstructural transformations exhibited significant influence on the magnetic moment of the alloy. Kinetics of non-isothermal crystallization was studied on the bases of isoconversional principle. Determination of kinetic triplets of individual crystallization steps, based on deconvolution of the complex DSC peaks applying Fraser-Suzuki function, enabled assessment of thermal stability of the alloy and kinetic predictions at different temperatures.
The thermodynamic properties and crystallization kinetics of the Co90Sc10 amorphous alloy prepared by rapid quench technique were investigated by X-ray diffractometer (XRD), differential scanning calorimeter (DSC), and simultaneous thermal analyzer (STA). In the isochronal heating process, the activation energy of crystallization is 388 kJ/mol, which was calculated by Kissinger method. The Johnson-Mehl-Avrami (JMA) model was used to describe the isothermal transformation kinetics. The variation of the activation energy of the isothermal process indicated that tiny Co particles precipitate out in the supercooled liquid region and become the nuclei of crystallization that reduce the activation energy at the beginning of crystallization process. Comprehensive results show that a-Co90Sc10 is a promising soft magnetic material for various applications.
In this paper, we present a novel MEMS orthogonal fluxgate sensor fabricated by standard micro fabricated technology. The sensor mainly consists of a three-dimensional solenoid pick-up coil and a meander-shaped Co-based amorphous ribbon core. The experimental results demonstrate that the sensitivity and noise can be optimized by tuning operation conditions with excitation current amplitude and frequency. The fabricated sensor exhibits a maximum sensitivity of 575 V/T, a wide linear range of ± 480 μT, and a perming below 0.8 μT for 90 mA rms sinusoidal excitation current at 500 kHz frequency. The equivalent magnetic noise is 0.20 nT/√Hz at 1 Hz, and the RMS noise is 1.09 nT in the frequency range of 0.1–10 Hz under the same excitation. In comparison with other micro fabricated fluxgates in similar dimensions, this device possesses relatively high sensitivity and low noise spectral density.