FeCo Particles Research Articles

Coupling RGO with magnetic components derived from basic ferric cobalt carbonate (BFCC) for efficient microwave absorption

In this work, reduced graphene oxide (RGO)-based composites loaded with magnetic CoFe2O4 (CFO) and CoFe were successfully synthesized via heat treatment of basic ferric cobalt carbonate (BFCC) under different temperatures. The impact of adding CFO and CoFe on the electromagnetic parameters and absorption properties was investigated. When 40 wt% CFO flakes and CoFe particles are added to the RGO matrix and the filler content is 20 wt% in paraffin, there gives a reflection loss of −48 dB with a 5.5 GHz absorption bandwidth at 2.1 mm thickness, and −50 dB with 4.8 GHz at 2.9 mm, respectively. The coupling of a magnetic medium can change the electromagnetic loss mechanism in the material, which ultimately affects the absorption properties of the material. This study provides a good basis for the design of composite materials of RGO as microwave absorbing materials, enabling large-scale production of high-performance absorption materials.

Crystallographic disorder-order transition of self-assembly FeCo mesocrystals independent of ligand

Mesocrystal with aligned small grains is an important type of block in building high performance artificial bulk materials. But it is difficult to obtain mesocrystal particles without the assistant of surface ligands due to their unclear formation process. In this study, mesocrystal FeCo nanoparticles were successfully synthesized by co-precipitation of Fe and Co atoms using hydrazine hydrate as reducing agent with an appropriate addition rate. A non-classic nucleation process and the formation of mesocrystal FeCo nanoparticles had been observed. Microstructure characterization reveals that the arrangement of grains inside particles gradually change from multi-orientation to mono-orientation with the change of addition rate of hydrazine. The hydrazine addition rate, ie the reducing rate of metal atoms plays an important role for the formation of mesocrystal particles. The obtained mesocrystal FeCo particles show good magnetic performance (the highest magnetization and lowest coercivity). The discovery of the influence of synthesis conditions on the formation of mesocrystals provide a useful way to control the microstructure and the performance of consisting nanostructures.

Characterization of magnetic FeCo particles with controlled bimetallic composition

In this study, six bimetallic FeCo particles were synthesized via the hydrothermal method, employing hydrazine hydrate as a reducing agent. These particles were synthesized at specific Fe:Co ratios of 1:0, 3:1, 1:1, 1:3, 1:9 and 0:1. The synthetic feeding of Fe:Co is of fundamental importance as it not only modulates the composition of the particles but also exerts control over their structural, morphological, and performance attributes. X-ray diffraction (XRD) analysis revealed that for particles synthesized from pure ferrous salt and pure cobalt salt, the former exhibited a Fe3O4 spinel structure, while the latter presented an hcp-type metallic Co structure. Conversely, for the remaining four Fe:Co synthetic feedings, the structure of FeCo bimetallic alloys exhibited a gradual transformation from an Fe-based bcc structure to a Co-based bcc structure, eventually culminating in a Co-based hcp structure as the Co content increased. Scanning electron microscopy (SEM) images indicated that particles prepared with a Fe:Co feeding ratio of 1:0 and 3:1 manifested as cube-shaped particles with approximate sizes of 200 nm and 100 nm, respectively. Particles synthesized with a 1:1 Fe:Co ratio exhibited pyramid-like shapes accompanied by small spinel structures. In contrast, those prepared with a 3:1 and 9:1 Fe:Co feeding ratio displayed a flower-like morphology with particle sizes around 10 µm, while particles synthesized using pure cobalt salts assumed a palm frond-like appearance. Moreover, the investigation into thermal stability established that FeCo alloy particles exhibited superior resistance to air oxidation when compared to pure Co particles. The magnetic studies indicated that all the particles were paramagnetic materials, with their magnetic properties being contingent on the composition. Notably, the particles synthesized with synthetic feedings of 1:1 and 3:1 exhibited the highest saturation magnetization of 151.80 emu·g−1 and the lowest saturation magnetization of 62.79 emu·g−1, respectively. These findings hold significant promise for the development of stable and finely-tailored magnetic particles with diverse potential applications in technology.

A Recyclable Co-Fe Bimetallic Immobilized Cellulose Hydrogel Bead (CoFeO@CHB) to Boost Singlet Oxygen Evolution for Tetracycline Degradation

In the current work, a novel Co-Fe bimetallic immobilized cellulose hydrogel bead (CoFeO@CHB) was prepared via in situ chemical precipitation followed by heat treatment and applied for tetracycline (TC) degradation in the presence of peroxymonosulfate (PMS). The characterization results indicated that the Co-Fe particles were evenly distributed within the porous cellulose hydrogel beads, without affecting their morphologies or crystal structures. During the TC degradation, the CoFeO@CHB/PMS system showed a high resistance and stability to different water bodies, and the common anions and natural organic matters showed a limited effect on TC degradation. The chemical quenching experiments (using chemicals to react with specific reactive species) as well as electron paramagnetic resonance (EPR) results showed that CoFeO@CHB can effectively active PMS to generate multiple reactive oxygen species (ROS, such as SO4•−, •OH and 1O2), in which the 1O2-dominated non-radical pathway played a vital role in TC degradation. Both Co and Fe were proposed as the active sites for PMS activation, and the CoFeO@CHB/PMS system showed a high potential in practical application due to its high selectivity and robustness with much less toxic intermediate products. Furthermore, a long-term continuous home-made dead-end filtration device was constructed to evaluate the stability and application potential of the CoFeO@CHB/PMS system, in which a >70% removal was maintained in a continuous 800 min filtration. These results showed the promising potential for cellulose hydrogel beads utilized as a metal-based nanomaterial substrate for organic degradation via PMS activation.

Novel Sr1.95Fe1.4Co0.1Mo0.5O6-δ anode heterostructure for efficient electrochemical oxidative dehydrogenation of ethane to ethylene by solid oxide electrolysis cells

The electrocatalytic conversion of ethane to ethylene is an important industrial process since ethylene is useful for the production of various chemical intermediates and polymers. However, this process often requires high temperatures. Metal-oxide heterogeneous interfaces constructed by in-situ exsolved process under reducing conditions would be favorable for promoting the catalyst activity, selectivity, and stability of ethane conversion to ethylene. Herein, Sr1.95Fe1.4Co0.1Mo0.5O6-δ (abbreviated as SFCoM) was prepared as a novel anode material of solid oxide electrolysis cells (SOECs) for green ethylene production by electrochemical oxidative dehydrogenation of ethane. After reduction, nano CoFe particles were in-situ exsolved on SFCoM oxides to form a nano alloy-oxide heterostructure (CoFe@SFCoM) with large numbers of reactive sites, relevant for improving the conversion rate of ethane and the yield of ethylene. At 800 °C, the single cell based on CoFe@SFCoM anode exhibited a current density of 1.89 A cm−2 at 1.6 V with an ethane conversion rate of 36.4% and corresponding ethylene selectivity of 94.5%. After 50 h of testing, the electrolysis current density(∼0.5 A cm−2) and ethylene yield(∼18.43%) of the single cell did not change significantly, showing good stability. In sum, CoFe@SFCoM looks very promising for future use as a SOECs anode for the electro-catalytic conversion of ethane to ethylene.

Construction of hollow and porous carbon Fiber/CoFe composites derived from strawberry petiole for enhanced microwave absorption

Biomass-derived materials have emerged as lightweight and high-efficiency carbon-based microwave absorber for their huge availability and multifarious microstructure. Herein, we synthesize a strawberry petiole derived carbon fiber (SCF) /magnetic CoFe composites (SCF/CoFe) via solvothermal reaction and calcination treatment. CoFe particles are densely and uniformly distributed on the surface of the uniform hollow and porous SCF. After adjusting the calcination temperature, SCF/CoFe sample with filler content of 15 wt% obtains a minimum reflection loss of −40.4 dB and a wide effective absorption bandwidth of 3.5 GHz at a thin thickness of only 2.0 mm. The hollow and porous structure and synergistic effect between conductive SCF and magnetic CoFe simultaneously contribute to the enhanced impedance matching and attenuation ability, which together result in the remarkable microwave absorption properties.

Preparation of FeCo/C-N and FeNi/C-N Nanocomposites from Acrylamide Co-Crystallizates and Their Use as Lubricant Additives.

FeCo and FeNi nanoalloy particles encapsulated in a nitrogen-doped carbonized shell (FeCo/C-N and FeNi/C-N) were synthesized by thermolysis at 400 °C of polyacrylamide complexes after frontal polymerization of co-crystallizate of Fe and Co or Ni nitrates and acrylamide. During the thermolysis of polyacrylamide complexes in a self-generated atmosphere, Co(II) or Ni(II) and Fe(III) cations are reduced to form FeCo and FeNi nanoalloy particles, while polyacrylamide simultaneously forms a nitrogen-doped carbon shell layer. This unique architecture provides high chemical and thermal stability of the resulting nanocomposites. The average crystallite size of FeCo and FeNi nanoparticles is 10 and 12 nm, respectively. The nanocomposites were studied by X-ray diffraction, atomic force microscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The nanocomposites have been tested as antifriction and antiwear additives in lubricating oils. The optimal concentrations of nanoparticles were determined, at which the antifriction and antiwear properties of the lubricant manifest themselves in the best possible way.

Facile Preparation of Light‐Weight Polyetheretherketone/Graphite/FeCo Ternary Heterogeneous Composite Foam with High Compressive Strength and Excellent Integrated Electromagnetic Wave Absorption Performance

AbstractThe preparation of the electromagnetic wave (EMW) absorbing materials with 3D porous structural, light weight, and high mechanical strength has been receiving greater attention for a long time. A series of light‐weight polyetheretherketone/graphite/FeCo ternary heterogeneous composite foams (PEEK/C/FeCo) with high mechanical strength are prepared via thermally induced phase separation. Based on the high compressive strength of PEEK resin and its stable skeleton formed by thermally induced phase separation, the composite foam has high compressive strength and low density. In addition, during the thermally induced phase separation process, porous structures are formed inside the PEEK, and graphite and FeCo particles are uniformly dispersed between the pore structures, the composite foams possess excellent porous structure, moderate dielectric loss, and magnetic loss, exhibiting good absorbing properties. With the low density of 0.49 g cm−3 and high compressive strength of 6.40 MPa, the as‐synthesized optimal sample (PEEK‐50/C‐40/FeCo‐10) achieves a minimum reflection loss up to −35.9 dB covering a bandwidth of 3.6 GHz for a thickness of 1.5 mm. In a word, this study provides a novel, economical, and efficient way to obtain a light foam with high mechanical strength and good EMW absorbing property.

Influence of Pr6O11 addition on structural and magnetic properties of mechanically alloyed Fe65Co35 nanoparticles

This work focuses on the synthesize of nanostructured (Fe65Co35)100-x (Pr6O11)x (x = 0, 5) powders using high energy ball milling. The influence of Pr6O11 on structural, morphological and magnetic properties of Fe65Co35 nanoparticles were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) with a dispersive energy analyzer (EDS), vibratory sample magnetometer (VSM) and differential scanning calorimetry (DSC). Results show that the praseodymium oxide addition increased the decrement rate of the crystallite size with milling time of about 27 % and decreased the increment rate of the internal micro-strain of 50 %. Moreover, because of its high grain fragmentation tendency, Pr6O11 increases the hardness and brittleness of Fe-Co powders. Moreover, it minimized the cold welding between Fe-Co ductile particles leading to a significant decrease in the average particle size (~1µm). The magnetic measurements conducted at room temperature show that the saturation magnetisation (Ms) and the coercivity (Hc) increased with milling time in both compositions. A low Ms and high Hc values were detected in (Fe65Co35)95 (Pr6O11)5 nanoparticles. The results demonstrated a soft ferromagnetic nature in all of the synthesized nanoparticles with Ms in the range 207 – 216 emu/g and Hc is found to be 113 Oe.

High-Performance Anisotropic Nanocomposites with a Novel Core/shell Microstructure.

Anisotropic nanostructures of magnetically hard and soft materials are fascinating for exploring next-generation ultrastrong permanent magnets with less expensive rare-earth elements. It is a big challenge fabricating high-performance nanocomposites due to the difficulty in controlling the grain size of the soft phase. Here, surfactant-assisted low-temperature chemical coating (LTCC) is adopted to fabricate SmCo5@FeCo nanocomposites. A uniform coating layer of the soft phase ranging from 5 to 15 nm FeCo particles is obtained. Both high coercivity Hc of 17.2 kOe and high energy product (BH)max of 29.4 MGOe in the optimal anisotropic SmCo5@FeCo nanocomposites with 15 wt % soft phase coating had been successfully fabricated, which has an enhancement of 31% compared with that of the uncoated single SmCo5 phase. The excellent performance is ascribed to nanosized grains of both soft and hard phases and a high remanence ratio Mr/Ms of 0.976. These results made a big step toward synthesizing a stronger bulk nanocomposite system.

Synergistic CoFe-Fe5C2 nanocrystal wrapped in N-doped carbon/carbon nanotubes as enhanced and CO-resistant electrocatalyst for methanol oxidation

Herein, a new metal organic framework MOF derived CoFe-Fe5C2 nanoparticles embedded nitrogen doped graphitized carbon/ nitrogen doped carbon nanotubes (CoFe-Fe5C2@NC/CNTs) heterostructures is successfully achieved through calcination in dicyandiamide atmosphere using Co/Fe-MOF as a precursor. The morphologies display that CoFe and Fe5C2 are uniformly dispersed in the framework of nitrogen doped carbon and dicyandiamide forms NCNTS using cobalt as a graphitization catalyst. The as prepared CoFe-Fe5C2@NC/CNTs hybrids exhibit remarkable specific properties of 60.23 mA cm−2 and small Tafel slope of 106.2 mV dec−1 in potential window from 0.4 V to 0.9 V towards methanol electro- oxidation reaction (MOR) in alkaline solution. At the same time, it realize more excellent stability comparing to that of CoFe-Fe5C2@NC electrocatalyst, which attributed to the interconnected ion/electron channels of abundant interfaces anchored nitrogen doped carbon nanotubes and the thin layer nitrogen doped graphitized carbon anchor the ultra-fine Fe5C2 and CoFe particles accelerating the charge transport. More importantly, CoFe-Fe5C2@NC presents 94.6% retention of initial MOR activity during CO poisoning test. This strategy will provide new ideas for the control of the composite structure of transition metal carbides using MOF derivatives, and provide technical support for the development of efficient and CO-resistant non noble metal electrocatalysts.

Carbon Fibers Embedded with Aligned Magnetic Particles for Efficient Electromagnetic Energy Absorption and Conversion.

Harvesting electromagnetic (EM) energy from the environment and converting it into useful micropower is a new and ideal way to eliminate EM radiation and while providing power for microelectronic devices. The key material of this technology is broadband, ultralight, and ultrathin EM-wave-absorbing materials, whose preparation remains challenging. Herein, a high magnetic field (HMF) strategy is proposed to prepare a biomass-derived CoFe/carbon fiber (CoFe/CF) composite, in which CoFe magnetic particles are aligned in CFs, creating magnetic coupling and fast electron transmission channels. The graphitization degree of CFs is improved via the "migration catalysis" of CoFe particles under HMF. The HMF-derived CoFe/CF shows a largely broadened EM wave absorption bandwidth under ultralight and ultrathin conditions (1.5 mm). Its absorption bandwidth increases 5-10 times compared with conventional CoFe/CF that has randomly distributed CoFe particles and surpasses the reported analogues. A device model for EM energy absorption and reuse is designed based on the HMF-derived CoFe/CF membrane, which exhibits a 300% higher capability than conventional CoFe/CF membrane in converting EM energy to thermal energy. This work offers a new strategy for the design and fabrication of broadband, ultrathin, and ultralight EM wave absorption materials and demonstrates a potential conversion approach of the waste EM energy.

Facile preparation and excellent microwave absorption properties of cobalt-iron/porous carbon composite materials

In this work, a cobalt-iron/biomass porous carbon (CoFe/BPC) composite material is prepared through a facile in situ reduction process using fir wood as the raw material. CoFe2O4 is successfully reduced to CoFe alloy by the BPC after the heat treatment process. The morphology characteristics indicate that the CoFe particles are uniformly distributed in the porous carbon matrix. Besides, compared to BPC and CoFe2O4/BPC samples, the CoFe/BPC composite material has higher dielectric and magnetic losses due to its carbon graphitization, porous structure, strong magnetism, and multicomponent effect. Electromagnetic (EM) wave absorption properties are determined in the frequency range of 8.2–12.4 GHz. The CoFe/BPC composite material has a minimum reflection loss of −53.6 dB at 10.9 GHz with a thickness of 2.2 mm. The results indicate that the CoFe/BPC composite material is expected to be a superior EM wave absorber. These encouraging findings provide insights into the preparation of promising practical applications of biomass-derived microwave absorbers.

One-step synthesis, characterization and properties of novel hybrid electromagnetic nanomaterials based on polydiphenylamine and Co-Fe particles in the absence and presence of single-walled carbon nanotubes.

A one-step preparation method for hybrid electromagnetic nanomaterials based on polydiphenylamine (PDPA) and bimetallic Co–Fe particles in the absence and presence of single-walled carbon nanotubes (SWCNT) was proposed. During IR heating of PDPA in the presence of Co(ii) and Fe(iii) salts in an inert atmosphere at T = 450–600 °C, the polycondensation of diphenylamine (DPA) oligomers and dehydrogenation of phenyleneamine units of the polymer with the formation of C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N bonds and reduction of metals by evolved hydrogen with the formation of bimetallic Co–Fe particles dispersed in a polymer matrix occur simultaneously. When carbon nanotubes are introduced into the reaction system, a nanocomposite material is formed, in which bimetallic Co–Fe particles immobilized on SWCNT are distributed in the matrix of the polymer. According to XRD data, reflection peaks of bimetallic Co–Fe particles at diffraction scattering angles 2θ = 69.04° and 106.5° correspond to a solid solution based on the fcc-Co crystal lattice. According to SEM and TEM data, a mixture of particles with sizes of 8–30 nm and 400–800 nm (Co–Fe/PDPA) and 23–50 nm and 400–1100 nm (Co–Fe/SWCNT/PDPA) is formed in the nanocomposites. The obtained multifunctional Co–Fe/PDPA and Co–Fe/SWCNT/PDPA nanomaterials demonstrate good thermal, electrical and magnetic properties. The saturation magnetization of the nanomaterials is MS = 14.99–31.32 emu g−1 (Co–Fe/PDPA) and MS = 29.48–48.84 emu g−1 (Co–Fe/SWCNT/PDPA). The electrical conductivity of the nanomaterials reaches 3.5 × 10−3 S cm−1 (Co–Fe/PDPA) and 1.3 S cm−1 (Co–Fe/SWCNT/PDPA). In an inert medium, at 1000 °C the residue is 71–77%.

Magnetic properties of FeCo-iron oxide core–shell nanoparticles investigated through first order reversal studies

Core–shell magnetic nanoparticles exhibit exchange bias, whereas the magnitude of the exchange bias field is influenced by various factors that are still under investigation. We present a detailed analysis of the magnetic behavior in Fe- and Co-rich FeCo particles with a ferrimagnetic oxide shell. The as-synthesized alloys, with an average particle size above 150 nm, show high saturation magnetization and exhibit multidomain nature. The magnetic behavior has been analyzed through first order reversal studies at room temperature, and low temperature (15 K) for the as-synthesized and size-reduced alloys. The size-reduced alloys exhibit exchange bias that enhances with decreasing average particle size and found to be maximum for the Co-rich FeCo. First order reversal curve (FORC) studies could resolve the reversible, irreversible magnetization components, and magnetostatic interactions. The low-temperature field cooled measurements expose random field bias acting at the interfaces. The studies reveal that FORC could be utilized to obtain information about particle size and its distribution dependent magnetic behavior in core–shell nanostructures.

High-throughput thermal plasma synthesis of FexCo1-x nano-chained particles with unusually high permeability and their electromagnetic wave absorption properties at high frequency (1-26 GHz).

Herein, we introduce novel 1-dimensional nano-chained FeCo particles with unusually-high permeability prepared by a highly-productive thermal plasma synthesis and demonstrate an electromagnetic wave absorber with exceptionally low reflection loss in the high-frequency regime (1-26 GHz). During the thermal plasma synthesis, spherical FeCo nanoparticles are first formed through the nucleation and growth processes; then, the high temperature zone of the thermal plasma accelerates the diffusion of constituent elements, leading to surface-consolidation between the particles at the moment of collision, and 1-dimensional nano-chained particles are successfully fabricated without the need for templates or a complex directional growth process. Systematic control over the composition and magnetic properties of FexCo1-x nano-chained particles also has been accomplished by changing the mixing ratio of the Fe-to-Co precursors, i.e. from 7 : 3 to 3 : 7, leading to a remarkably high saturation magnetization of 151-227 emu g-1. In addition, a precisely-controlled and uniform surface SiO2 coating on the FeCo nano-chained particles was found to effectively modulate complex permittivity. Consequently, a composite electromagnetic wave absorber comprising Fe0.6Co0.4 nano-chained particles with 2.00 nm-thick SiO2 surface insulation exhibits dramatically intensified permeability, thereby improving electromagnetic absorption performance with the lowest reflection loss of -43.49 dB and -10 dB (90% absorbance) bandwidth of 9.28 GHz, with a minimum thickness of 0.85 mm.

Synthesis, oxidation resistance and microwave absorbing properties of FeCo-based heterostructures

The fabrication of a shell on the surfaces of ferromagnetic particles has been proved to be an efficient approach to tailoring and improving the electromicrowave (EM) absorption. In this study, core–shell composites (FeCo@SiO2/TiO2, FeCo@SiO2@TiO2) were designed and fabricated by facile hydrolysis reactions. In these novel composites, the combined effects of the characteristics of each component result in excellent properties. The FeCo core exhibits strong magnetic loss, and the SiO2/TiO2 shell not only acts as an impedance matching medium, but also exhibits excellent dielectric loss. Moreover, the SiO2 and TiO2 can efficiently limit direct contact between FeCo particles and protect the FeCo core from oxidation at high temperature. The FeCo@SiO2, FeCo@TiO2, and FeCo@SiO2@TiO2 absorbers exhibit enhanced EM absorption, with maximum reflection losses (RLmax) of −38.49, −36.53, and −33.72 dB at thicknesses d of 2, 5, and 3 mm, respectively, compared to −19.23 dB for FeCo single particles (d = 5 mm). The improvement is due mainly to the improved impedance matching and multiple interfacial polarization. In particular, after annealing at 500 °C, the RLmax values of the FeCo@SiO2, FeCo@TiO2, and FeCo@SiO2@TiO2 absorbers are −25.41, −24, and −32.38 dB at thicknesses of 3, 3, and 5 mm, respectively, which are much higher than that of uncoated FeCo (−1.39 dB, d = 5 mm). These findings demonstrate that the fabricated FeCo-based core–shell structures can be good candidates for use as room- and high-temperature EM absorbers.

Magnetostatic properties of assembly of magnetic vortices

The ultrasonic oscillation of a macroscopic sample in a viscous liquid is used to create magnetic particles of FeCo alloy with an average diameter D ~100 nm. The FeCo particles obtained have a high specific saturation magnetization, Ms = 1960 emu/cm3, close to that of a bulk sample. The hysteresis loop of a magneto-polymer composite prepared from FeCo particles shows low coercive force and a remanent magnetization close to zero. The magnetic saturation of the magnetic composite samples is achieved in a sufficiently strong magnetic field, H = 6.5 kOe. The hysteresis loop features of the magnetic composite have been explained by means of the numerical simulation of the quasistatic hysteresis loops of non-oriented dilute assemblies of spheroidal FeCo particles with various aspect ratios.

Low-loss and high-induction Fe-based soft magnetic composites coated with magnetic insulating layers

Abstract We have provided a new and simple coating strategy to fabricate high-performance metal-based magnetic composites exhibiting both high magnetic inductions and decreased core loss. High-purity submicron FeCo particles have been dispersed into silicone resin to form a magnetic insulating film, which is then coated uniformly on the particle surface of high-purity Fe powders with a particle size of 170 μm to form new-type Fe-based soft magnetic composites (SMCs). These insulated magnetic layers containing submicron FeCo particles in these Fe-based SMCs can maintain very high saturated magnetization (209 A·m2·kg−1) for the composites, and also result in their low core loss. For traditional metal-based SMCs, the low core loss is often obtained accompanying with seriously decreased magnetic inductions. In present work, both high magnetic inductions and decreased core loss in company with high compacted density are achieved in these Fe-based SMCs coated with magnetic insulating coating layers. Specifically, the extremely low eddy current loss occurring in these new Fe-based SMCs enables their latent applications in low-loss and high-power magnetic devices.

Exchange Bias in Chemically Reduced FeCo Alloy Nanostructures

The equiatomic FeCo alloy with average particle sizes of 140 and 30 nm is obtained using an instant chemical reduction process. The mean hyperfine field of 36.0(5) T estimated from 300 K 57Fe Mössbauer spectra is consistent with a disordered FeCo phase with a relative fraction of 90(2)% for both the samples, along with γ‐Fe2O3. A CoO shell with an average thickness of 2.7 nm is inferred from transmission electron microscopy in the size‐reduced FeCo. The room temperature coercivity of the size‐reduced FeCo is higher than the expected theoretical values. An exchange bias field (HE of 296 Oe), vertical remanence shift at 15 K, and an exchange bias blocking temperature of 150 K are exhibited by the 30 nm FeCo particles. The observed HE and its temperature dependence are fairly explained based on a random field model.