FeCo Phase Research Articles

Magnetic anisotropy and microscopy studies in magnetostrictive Tb-(Fe,Co) thin films

This paper reports the effect of the film thickness on the magnetostrictive behavior of (Fe,Co) rich Tb-(Fe,Co) films grown on Si ⟨100⟩ by electron beam evaporation. Magnetostriction was found to decrease with an increase in film thicknesses. To understand the variation of magnetostriction with the film thickness, detailed structural, microstructural, magnetization, and magnetic microscopy studies were carried out. X-ray diffraction studies indicated the presence of two phases, viz., Tb2 (Fe, Co)17 and Fe-Co phases, for all the films. With the increase in the film thickness, the peak intensity of the Tb2 (Fe, Co)17 phase decreased and that of the Fe-Co phase increased. Magnetization studies showed the presence of strong in-plane anisotropy for all the films. In addition to this, the presence of the out-of-plane component of magnetization was also observed for the films grown with higher thicknesses. This anisotropic behavior was also validated through magnetic microscopy studies carried out along the in-plane and out-of-plane directions employing magneto-optic Kerr microscopy and magnetic force microscopy, respectively. The decrease in magnetostriction was explained on the basis of dual phase formation and complex interplay between the in-plane and out-of-plane magnetic anisotropies present in the film.

Simulation of alnico coercivity

Micromagnetic simulations of alnico show substantial deviations from Stoner-Wohlfarth behavior due to the unique size and spatial distribution of the rod-like Fe-Co phase formed during spinodal decomposition in an external magnetic field. The maximum coercivity is limited by single-rod effects, especially deviations from ellipsoidal shape, and by interactions between the rods. Both the exchange interaction between connected rods and magnetostatic interaction between rods are considered, and the results of our calculations show good agreement with recent experiments. Unlike systems dominated by magnetocrystalline anisotropy, coercivity in alnico is highly dependent on size, shape, and geometric distribution of the Fe-Co phase, all factors that can be tuned with appropriate chemistry and thermal-magnetic annealing.

Failure Mechanism of a Stellite Coating on Heat-Resistant Steel

The Stellite 21 coating on the heat-resistant steel X12CrMoWVNbN10-1-1 (so-called COSTE) used in a steam turbine valve was found to be fatigue broken after service at around 873 K (600 °C) for about 8 years. In order to investigate the failure mechanism, a fresh Stellite 21 coating was also prepared on the same COSTE steel substrate by using the similar deposition parameters for comparison. It was found that the Stellite 21 coating was significantly diluted by the steel, resulting in a thin Fe-rich layer in the coating close to the fusion line. Such high Fe concentration together with the incessant Fe diffusion from the steel substrate to the coating during the service condition (about 873 K (600 °C) for long time) induced the eutectoid decomposition of the fcc α-Co(Fe,Cr,Mo) solid solution, forming an irregular eutectoid microstructure that was composed of the primitive cubic α′-FeCo(Cr,Mo) phase and the tetragonal σ-CrCo(Fe,Mo) phase. The brittle nature of such α′/σ eutectoid microstructure contributed to the fatigue fracture of the Stellite 21 coating, resulting in an intergranular rupture mode.

Effects of minor precipitation of large size crystals on magnetic properties of Fe-Co-Si-B-P-Cu alloy

Abstract Nanocrystalline Fe81.3Co4Si0.5B9.5P4Cu0.7 alloy shows low coercivity (Hc 60 A/m). In terms of structure both the alloys in as-quenched state exhibit similar X-ray diffraction patterns (i.e. X-ray amorphous). Similar to low concentration of Co in the alloy, it is possible to realize a fine nanocrystalline structure made from bcc Fe-Co phase for higher concentration of Co. However, existence of a very few large sized crystals (above 100 nm) in as-quenched state enhances the Hc. A large numbers of bcc Fe(-Co) nuclei (∼2–5 nm) in as-quenched state results in a high magnetic flux density (Bs) after optimum annealing. It is possible to obtain a Bs of 1.88–1.90 T in this system but it is at the cost of an increase in Hc.

Internal dipolar field and soft magnons in periodic nanocomposite magnets

We study spin wave excitations in a three-dimensional nanocomposite magnet of exchange coupled hard (SmCo5) and soft (FeCo) phases. The dipolar interaction splits the spin wave energies into the upper and lower branches of the spin wave manifold. When the amount of the soft phase is increased the energy of low-lying spin excitations is considerably softened due to two reasons: (i) the low- lying mode locked into the soft phase region with a spin wave gap at k=0 which scales approximately proportional to the anisotropy constant of the soft phase and (ii) the internal dipolar field which comes from magnetic charges forming at hard-soft boundaries with normals parallel to the magnetization displaces the spin wave manifold toward the lower energies. With adding more soft phase the spin wave gap closes and the system moves to another ground state characterized by the magnetization mismatch between spins of the hard and soft phases.

Synthesis of C5+ hydrocarbons from low H2/CO ratio syngas over silica supported bimetallic Fe-Co catalyst

In the present study, selective synthesis of C5+ hydrocarbons from a low hydrogen to carbon mono oxide ratio syngas has been studied over a novel Fe-Co bimetallic catalysts. Fe was added into Co catalyst to increase the H2/CO ratio internally via increased water gas shift activity. Catalyst with varying Fe/Co composition (Fe/Co (w/w)=0.25, 0.5, 1) and varying metal loadings were prepared in the laboratory. Catalysts activity were tested in a fixed bed reactor at T–220°C, P–20bar, H2/CO–1.48 and GHSV–1200mL/h-gcat. Detail characterization of the catalysts were done through different techniques. Quantitative and qualitative analysis of the liquid products were done using GCMS and CHNS analyzers. The presence of Fe in bimetallic catalyst resulted an increase in CO conversion and product selectivity in comparison to that of mono metallic Fe/Co catalysts. Formation of Fe-Co bimetallic phase was confirmed through the detail characterization of fresh and spent catalysts which facilitate the CO adsorption on active metal sites. However, phases for individual iron and cobalt were also evident at higher metal loadings. The CO conversion increases with metal loading and was maximum at 30% metal loading. Optimum ratio of Fe/Co was 0.5 at a total metal loading of 30% (Cat-2) in which maximum (65%) CO conversion was achieved. Enhancement of H2/CO ratio through WGS reaction was examined over Cat-2 at various temperature and inlet H2/CO ratio. At 240°C, C5+ selectivity was maximum at the expense of CO2 and methane production.

Magnetic Behaviour of FeCo/Cu Core Shell Nanoparticles

In the present investigation, FeCo/Cu core shell nanoparticles were prepared by coating a Cu layer over FeCo alloy nanoparticles through displacement reaction. X-ray diffraction studies confirmed the presence of FeCo and Cu phases in the sample. The grain size and lattice strains of the core shell nanostructures were evaluated from the x-ray profiles by using single line profile analysis technique. The effect of annealing temperature on the magnetic properties of the core shell nanoparticles was studied by using a vibrating sample magnetometer. The results showed that the magnetic properties improve significantly after annealing the compacts of core shell nanoparticles under a magnetic field. Enhancement in magnetization was observed in the compacts with the increase in annealing temperature. Highest saturation magnetization value of 56 emu/g was recorded in the sample which was annealed at 600°C. It has been also found that the blocking temperature of the core shell nanoparticles increases with the increase in annealing temperature.

Polyacrylonitrile-based FeCo/C nanocomposites: Preparation and magnetic properties

Metal–carbon nanocomposites that represent FeCo alloy nanoparticles uniformly distributed over the carbon matrix, were prepared by the IR pyrolysis of precursors comprising polyacrylonitrile (PAN), iron acetylacetonate, and cobalt acetate (the metal ratio in the precursors was Fe: Co = 1: 1, 3: 1). The composition of FeCo alloy nanoparticles satisfies the tailored ratio Fe: Co. The FeCo phase is formed at synthesis temperatures in the range 500–600°С; at T ≤ 500°С only FCC-Co-base solid solutions are observed. The nanocomposites prepared at T ≥ 600°С simultaneously contain FeCo intermetallic nanoparticles and an insignificant amount of a FCC-Co phase or a cobalt-base solid solution phase. The saturation magnetization of FeCo/C metal–carbon nanocomposites is determined by the mean nanoparticle size and the alloy composition, and ranges from 36 to 64 (A m2)/kg (when Fe: Co = 1: 1) and from 35 to 52 (A m2)/kg (when Fe: Co = 3: 1) at synthesis temperatures in the range 600–800°С.

Synthesis, Morphology Control and Electromagnetic Wave Absorption Properties of Electrospun FeCo Alloy Nanofibers.

Recently, increasing interest has been focused on one-dimensional (1 D) magnetic nanomaterials that have significant anisotropic electromagnetic parameters and size effects that can be used to achieve improved shielding efficiency. In this study, the simple, low-cost and scalable synthesis of FeCo nanofibers is demonstrated by combining an electrospinning process with sequential thermal treatment involving calcination in air followed by reduction in H2 atmosphere. A citric acid has an influence on the morphology of the electrospun product. The as-spun precursor nanofibers are transformed into CoFe2O4 and FeCo phases through the sequential thermal treatment while maintaining the fibrous shapes. To evaluate the electromagnetic (EM) wave-absorbing abilities of the FeCo nanofibers, epoxy matrix composites with the nanofibers are fabricated. The composites show excellent EM wave absorption properties where the power loss of the FeCo nanofibers increased to 20 GHz without any degradation.

Impact of the B2 ordering behavior on the mechanical properties of a FeCoMo alloy

A Fe - 25at% Co - 9at% Mo alloy can be hardened by nm-sized (Fe, Co)7Mo6 µ-phase precipitates which is accomplished by solution annealing in the austenite region followed by rapid quenching to room temperature and subsequent aging below the austenite transition temperature. In overaged condition the Mo-content in the remaining matrix drops towards zero and, therefore, the matrix consist of 71at% Fe and 29at% Co. The binary Fe-Co system shows a disorder-order, A2↔B2 transition at a critical ordering temperature between 25at% and 72at% Co. It is expected that the remaining matrix of an overaged Fe - 25at% Co - 9at% Mo alloy also exhibits such an ordering reaction. It will be demonstrated that the formation of a B2 ordered FeCo phase can be delayed or completely prevented by rapid quenching from temperatures above the critical ordering temperature. This has a strong impact on the mechanical properties of this alloy which have been studied by means of tensile, impact toughness and hardness testing. The evidence for a disorder-order transition in this alloy has been given by neutron diffraction as well as high resolution transmission electron microscopy.

Phase transformation controlled tetragonality of MnNi-based nanocrystals

The phase transformation controlled tetragonality of MnNi nanostructures has attracted wide interest for their shape memory effect. In this study, MnNi nanocrystals were selected to epitaxially grow an FeCo shell, where the antiferromagnetic L10 phase transformation of the MnNi core triggers the tetragonal distortion in the magnetically soft FeCo shell. The tetragonality change of L10 MnNi under thermal annealing enables the control of the tetragonality of the FeCo phase, ultimately increasing magnetocrystalline anisotropy and coercivity. This study opens up a new route to fabricate functional nanostructures with unique magnetic properties.

Magnetic properties and phase evolution of sintered Nd-Fe-B magnets with intergranular addition of Pr–Co alloy

The magnetic properties, thermal stability and phase evolution of sintered Nd-Fe-B magnets with intergranular addition of Pr–Co were investigated. The thermal stabilities of coercivity and remanence were simultaneously enhanced without heavy rare earth elements, resulting from the partial substitution of Pr for Nd and Co for Fe in matrix phase, respectively. After Pr–Co addition, RE-rich phase reduced and new phases containing Pr and Co, such as (NdPr) (FeCo)2 (NdPr)3(FeCo) and (NdPr)2(FeCo)17 phases, were formed. With the increase of Pr–Co addition amount, intrinsic coercivity firstly decreased sharply which was mainly caused by the formation of soft ferromagnetic (NdPr) (FeCo)2 phase, and subsequently presented a remarkable recovery induced by the formation of non-magnetic (NdPr)3(FeCo) phase and transformation of (NdPr) (FeCo)2 phase from ferromagnetic to non-magnetic. Due to the reduction of matrix phase proportion, the remanence decreased monotonously after the addition of Pr–Co for more than 10 wt. %.

Direct writing of CoFe alloy nanostructures by focused electron beam induced deposition from a heteronuclear precursor

Recently, focused electron beam-induced deposition has been employed to prepare functional magnetic nanostructures with potential in nanomagnetic logic and sensing applications by using homonuclear precursor gases like Fe(CO)5 or Co2(CO)8. Here we show that an extension towards the fabrication of bi-metallic compounds is possible by using a single-source heteronuclear precursor gas. We have grown CoFe alloy magnetic nanostructures from the HFeCo3(CO)12 metal carbonyl precursor. The compositional analysis indicates that the samples contain about 80 at% of metal and 10 at% of carbon and oxygen. Four-probe magnetotransport measurements are carried out on nanowires of various sizes down to a width of 50 nm, for which a room temperature resistivity of 43 μΩcm is found. Micro-Hall magnetometry reveals that 50 nm × 250 nm nanobars of the material are ferromagnetic up to the highest measured temperature of 250 K. Finally, the transmission electron microscopy (TEM) microstructural investigation shows that the deposits consist of a bcc Co-Fe phase mixed with a FeCo2 O4 spinel oxide phase with nanograins of about 5 nm diameter.

Effect of Processing of HIPERCO® 50 Alloy Laminates on Their Magnetic Properties

Fe-Co-based soft-magnetic materials form an important class of high-induction alloys that are widely used in energy conversion applications in the aerospace industry. In this work, the effect of processing—cut method [stamping and wire-electrical discharge machining (EDM)] and annealing (cut unannealed, cut followed by annealing, and annealing followed by cut)—on the magnetic properties of the HIPERCO® 50 Alloy laminates was investigated. A cold-rolled ∼0.006-in (∼150-μm)-thick strip of HIPERCO® 50 Alloy was cut into ring laminations and final-annealed in dry hydrogen. Scanning electron microscopy (SEM) and x-ray diffraction analysis indicated the presence of extraneous Cu on the cut edge of the wire-EDM cut ring laminates, along with the expected Fe-Co phase for HIPERCO® 50 alloy. SEM micrographs of the cut edge showed the typical sheared surface and irregular surface for stamped and wire-EDM cut ring laminates respectively. The rings that were stamped followed by annealing (STfA) showed superior direct current (DC) and alternating current (AC) magnetic properties. The presence of Cu (diamagnetic) in wire-EDM cut rings adversely affects induction (B) and core loss (P T), compared to the stamped rings for corresponding annealing conditions. The difference in the DC magnetic properties between the ring laminates STfA and annealed followed by stamping (AfST) was significantly large compared to that between the ring laminates that were wire-EDM cut followed by annealing (EDfA) and annealing followed by wire-EDM (AfED). This suggests that, for certain applications where the differences in DC magnetic properties between EDfA and AfED are acceptable, the AfED rings may be put to application/service after the wire-EDM cut operation, i.e. wire-EDM may be performed after ‘final-annealing’. However, the AC properties between EDfA and AfED rings were significantly different, hence for AC applications, the ‘final annealing’, post-cutting, is critical irrespective of the cut method. Wire-EDM incorporates extraneous Cu on the cut edge of the HIPERCO® 50 Alloy laminates and deteriorates its magnetic properties. An intermediate grinding step after wire-EDM, for the removal of Cu, could probably improve the magnetic properties. However, if the extraneous Cu and the accompanied deterioration in magnetic properties is acceptable for certain applications, then the wire-EDM provides the flexibility to have the ‘final-annealing’ of HIPERCO® 50 Alloy laminates either before or after wire-EDM.

Investigations of Magnetic Properties Through Electrodeposition Current and Controlled Cu Content in Pulse Electrodeposited CoFeCu Nanowires

CoFeCu nanowires were deposited by pulsed electrodeposition technique into the porous alumina templates by a two-step mild anodization technique, using the single-bath method. The electrodeposition was performed in a constant electrolyte while Cu constant was controlled by electrodeposition current. The electrodeposition current was 3.5, 4.25, 5 and 6 mA. The effect of electrodeposition current and annealing on the magnetic behavior of the nanowires was investigated. Nanowires were fabricated with 30nm diameter and 100nm inter-pore distance with both bcc-CoFe and fcc- Cu phases. With increasing the electrodeposition current the Cu content decrease and the coercivity and magnetization increase up to its optimum value, then decrease. Annealing improved the coercivity, maximum coercivity was obtained for sample fabricated at 5 mA current. After annealing the magnetization decrease for all sampls. The X-ray diffraction pattern of the sample at electrodeposition current 3.5 mA after annealed indicates that Cu and CoFe phases separately was formed and separate peak related to CoFeCu alloy structure is not seen.

Preparation and Magnetic Properties of Nanocrystal Bulk SmCo<sub>7</sub> Magnets

Two kinds of 2:17R Sm-Co alloys, Sm2(Fe,Cu,Zr,Co)17 and pure binary Sm2Co17 were prepared, and the amorphous powder was prepared by high-energy ball milling Sm-Co alloys. The bulk nanocrystalline SmCo7 was prepared by hot-pressing the amorphous powder, and the magnetic properties and phase composition were studied. Initial Sm2(Fe,Cu,Zr,Co)17 showed a large value of coercivity while the pure Sm2Co17 almost showed no coercivity. However, after ball milling the grain size of alloys decreased dramatically until completely amorphous. Two kinds of alloys showed the different phase composition and magnetic properties after hot-pressing. It was found that the pure Sm2Co17 bulk magnet showed a high coercivity Hc and had the 1:7H phase. On the other hand, the Sm2(Fe,Cu,Zr,Co)17 showed high saturation magnetization Ms and very low Hc since the Fe-Co and Sm2Co3 phase were precipitated from the alloy.

Spontaneously formed interfacial metal silicates and their effect on the magnetism of superparamagnetic FeCo/SiO₂ core/shell nanoparticles.

The integration of superparamagnetic core/shell nanoparticles into devices and other nanoscale technological applications requires a detailed understanding of how the intimate contact between core and shell nanophases affects the magnetism. We report how, for single-domain FeCo nanoparticles, an FeCo phase unique to the nanoscale with silica shells of increasing thicknesses spontaneously formed interfacial metal silicates between the core and shell (such as Fe2SiO4 and Co2SiO4) and altered the overall magnetism of the nanomaterial significantly. The influence of this previously overlooked phenomenon on magnetic properties is reported. Evidence of these metal silicate interfacial layers was observed by X-ray absorption spectroscopy (XAS) collected over the L3,2 absorption edges of Fe and X-ray photoelectron spectra (XPS) collected over the 2p transitions of Fe and Co. Through the correlation of magnetometry and XPS data, the evolution of nanoparticle magnetic anisotropy is shown to increase with the metal silicate.

A lithiation/delithiation mechanism of monodispersed MSn5 (M = Fe, Co and FeCo) nanospheres

The same crystal structure, identical particle surface morphology and the similar particle size distribution of MSn5 (M = Fe, Co and FeCo) phases are ideal for comparison of the electrochemical performance, reaction mechanism, thermodynamics and kinetics.

Effect of Co addition on crystallization and magnetic properties of FeSiBPCu alloy

The effects of Co addition on the microstructure, crystallization processes and soft magnetic properties of (Fe1−xCox)83Si4B8P4Cu1 (x=0.35, 0.5, 0.65) alloys were investigated. The experimental results demonstrated that the addition of Co decreased the thermal stability against crystallization of the amorphous phase, and thus improved the heat treatment temperature of this alloy. FeCoSiBPCu nanocrystalline alloys with a dispersed α′-FeCo phase were obtained by appropriately annealing the as-quenched ribbons at 763K for 10min. The α′-FeCo with grains size ranging from 9 to 28nm was identified in primary crystallization. The coercivity (Hc) markedly increased with increasing x and exhibited a minimum value at x=0.35, while the saturation magnetic flux density (Bs) shows a slight decrease. The (Fe0.65Co0.35)83Si4B8P4Cu1 nanocrystalline alloy exhibited a high saturation magnetic flux density Bs of 1.68T, a low coercivity, Hc of 5.4A/m and a high effective permeability µe of 29,000 at 1kHz.

Correlation Between Chemical Composition and Adherence of Cr and Co Coatings Deposited by Electric Arc

This paper presents the adhesive strength of FeCr and FeCoCr coatings produced by electric arc thermal spray process on carbon steel plates. Carbon steels are not resistant to corrosion and several methods are used in surface engineering to protect them from aggressive environments such as the marine one. The main objective of this work is the evaluation of the mechanical and metallurgical properties of coatings produced by thermal spray on carbon steel. Five chemical compositions were tested in order to give a large panel of possibility. Coatings were characterized by several methods to result in a screening of performance. The physical properties of coatings were also evaluated by adhesion quantification, using pull-off test, and microhardness measurement. The assessment of microstructural morphology by X-ray diffraction (XRD) and scanning electron microscopy (SEM) was made. The open circuit potential was monitored to evaluate the corrosion tendency. SEM results showed uniformity in the deposited layer and low amount of oxide and porosity. The adhesive strength of FeCoCr alloy coatings was higher than other coating conditions. In the immersion test, all sealed conditions presented high corrosion potential. Semi-quantitative phase calculation was performed by the Rietveld method using XRD. The presence of FeCr, FeCo, and austenite phases was determined. Based on the performed characterizations, the findings suggested that the FeCrCo deposition, with an epoxy sealing, is suitable to be used as an efficient coating of carbon steel in aggressive corrosive environments.