Pure CoFe Research Articles

CoFeMn0.5Al0.25: A high magnetisation CoFe based soft alloy with reduced Co content

The high cost of CoFe alloys has prevented their widespread use regardless of their promising properties such as high magnetisation, high Curie temperature, as soft magnetic materials for high temperature applications. Here, it is shown that AlMn can be used to create a CoFeMn0.5Alx alloy, which has reduced Co content but comparable soft magnetic properties as CoFe alloys, therefore providing a more economical alternative to pure CoFe soft magnets.

Enhanced peroxidase-like activity of 2(3), 9(10), 16(17), 23(24)-octamethoxyphthalocyanine modified CoFe LDH for a sensor array for reducing substances with catechol structure.

Improving the catalytic activity of artificial nanozymes to realize the real-time detection of small molecules becomes an important task. Herein, a highly active nanozyme, 2(3), 9(10), 16(17), 23(24)-octamethoxyphthalocyanine (Pc(OH)8) modified CoFe LDH microspheres (Pc(OH)8-CoFe LDH) have been prepared by the two-step hydrothermal method. The 3,3',5,5'-tetramylbenzidine (TMB), a chromogenic substrate, was fast oxidized into blue oxTMB by H2O2 in the presence of Pc(OH)8-CoFe LDH, indicating that Pc(OH)8-CoFe LDH possesses high peroxidase-like activity rather than pure CoFe LDH. The enhancement peroxidase-like activity of the Pc(OH)8-CoFe LDH is ascribed tothe synergistic action between Pc(OH)8 and CoFe LDH. Experimental results of radical scavenger and fluorescence probe verify that superoxide radical (•O2-) plays an important role during the catalytic reaction. Interestingly, the absorption intensity of reaction system has been enhanced largely, due to adding of the reducing substances containing catechol structure. Based on this, the three reducing substances (dopamine, procyanidin B2, catechins) containing catechol structure were distinguished from other reducing substances without catechol structure. Thus, a colorimetric array has been constructed using reaction time as the sensing element to realize the sensitive and selective recognition of catechol structures at a certain concentration.

A general confinement co-assembly strategy enabling cross-dimensional supraspheres for boosting electrochemical performance

The bottom-up assembly utilizing nanocrystals (NCs) as building blocks is a highly anticipated approach to access novel metamaterials. Limited by the library of binary spherical assembly, colloidal components of building blocks are necessarily extended for targeting the desired assembled-superstructure with emergent properties. Here, a generalized approach is presented that carbon nanotubes (CNTs) capped with long-chain hydrocarbon ligands, as creative colloidal components, can be compatibly co-assembled with various NCs into binary supraspheres based on a confinement microemulsion environment. Such cross-dimensional assemblies possess the structural merits of excellent conductivity, abundant voids and high stability, thus synergistically boosting its electrochemical performance. As a proof of concept, the co-assembled CoFe 2 O 4 /CNTs supraspheres exhibit extraordinary capacity (890 mAh g −1 at 0.5 A g −1 ), rate capability (318 mAh g −1 at 20 A g −1 ), and structural stability (458 mAh g −1 at 5 A g −1 after 1000 cycles) relative to pure CoFe 2 O 4 when evaluated in Li-ion battery. Beyond that, its derived phosphides CoFeP/CNTs assemblies outperform most of the state-of-art electrodes when acting as electrocatalysts for hydrogen evolution reactions (HER). This work provides a new perspective for constructing superstructures of NCs for potential applications in energy storage devices.

Effect of hafnium-incorporation on the microstructure and dielectric properties of cobalt ferrite ceramics

Abstract The effect of hafnium (Hf) incorporation on the crystal structure, surface morphology, chemical composition and dielectric properties of cobalt ferrite (CoFe 2 O 4 ) is reported. Hafnium incorporated Co-ferrite (CoFe 2− x Hf x O 4 ) ceramics were prepared by varying the Hf concentration in the range of x =0.0–0.2. X-ray diffraction (XRD) studies indicate that the CoFe 2− x Hf x O 4 ceramics crystallize in inverse spinel change to structure similar to that of pure CoFe 2 O 4 . Hafnium incorporation induces lattice expansion leading to increased lattice constant from 8.374 A for pure CoFe 2 O 4 to 8.391 A for the highest Hf concentration ( x =0.2) in CoFe 2− x Hf x O 4 . Dielectric constant of CoFe 2− x Hf x O 4 ceramics is also enhanced compared to pure CoFe 2 O 4 due to the lattice distortion upon Hf incorporation. Improved dielectric properties of CoFe 2− x Hf x O 4 ceramics compared to pure CoFe 2 O 4 is attributed to the lattice distortion due to larger Hf-ions substituting for smaller Fe-ions associated structural changes with increased Hf concentration. Frequency variation of the dielectric constant shows the dispersion that can be modeled with a modified Debye's function, which considers the possibility of more than one ion, contributing to the relaxation.

Controlled Synthesis and Magnetic Properties of Bimagnetic Spinel Ferrite CoFe2O4 and MnFe2O4 Nanocrystals with Core–Shell Architecture

A combination of hard phase CoFe(2)O(4) and soft phase MnFe(2)O(4) as the bimagnetic nanocrystals in a core-shell architecture has been synthesized, and their magnetic properties have been systematically studied. Both HRTEM and EDS results confirmed the formation of bimagnetic core-shell structured nanocrystals. On the basis of the systematic and comparative studies of the magnetic properties of a mechanical mixture of pure CoFe(2)O(4) and MnFe(2)O(4) nanocrystals, chemically mixed Co(1-x)Mn(x)Fe(2)O(4) nanocrystals, and bimagnetic core-shell CoFe(2)O(4)@MnFe(2)O(4) and MnFe(2)O(4)@CoFe(2)O(4) nanocrystals, the bimagnetic core-shell nanocrystals show very unique magnetic properties, such as the blocking temperature and coercivity. Our results show that the coercivity correlates with the volume fraction of the soft phase as the theoretical hard-soft phase model has suggested. Furthermore, switching the hard phase CoFe(2)O(4) from the core to the shell shows great changes in the coercivity of the nanocrystals. The bimagnetic core-shell nanocrystals evidently demonstrate the rational design capability to separately control the blocking temperature and the coercivity in magnetic nanocrystals by varying the materials, their combination, and the volume ratio between the core and the shell and by switching hard or soft phase materials between the core and shell. Such controls via a bimagnetic core-shell architecture are highly desirable for magnetic nanocrystals in various applications.

Magnetic and magnetostrictive behavior of Dy 3+ doped CoFe 2O 4 single crystals grown by flux method

We studied the effect of Dy 3+ content on the magnetic properties of cobalt ferrite single crystal. The single crystals of CoFe 1.9Dy 0.1O 4 were grown by the flux method using Na 2B 4O 7.10 H 2O (Borax) as a solvent (flux). The black and shiny single crystals were obtained as a product. The X-ray diffraction analysis at room temperature confirmed the spinel cubic structure with lattice constant a=8.42 Å of the single crystals. The compositional analysis endorses the presence of constituents Co, Fe and Dy elements after sintering at 1300 °C within the final structure. The magnetic hysteresis measurements at various temperatures viz. 10 K, 100 K, 200 K and 300 K reveal the soft ferrimagnetic nature of the single crystal than that of for pure CoFe 2O 4. The observed saturation magnetization ( M s ) and coercivity ( H c ) are found to be lower than that of pure CoFe 2O 4 single crystal. The magnetostriction ( λ) measurement was carried out along the [001] direction. The magnetic measurements lead to conclude that the present single crystals can be used for magneto-optic recording media.

Air-oxidation of a Co-based amorphous ribbon at 400–600 °C

The oxidation behavior of a commercial Co 69B 12Si 12Fe 4Mo 2Ni 1 amorphous ribbon (Co6-AR) was studied over the temperature range of 400–600 °C in dry air. The results showed that virtually no oxidation occurred at 400 °C. On the other hand, the oxidation kinetics of the Co6-AR alloy at 450–600 °C generally followed a multi-stage parabolic-rate law, and the parabolic-rate constants ( k p values) tend to increase with increasing temperature. It was found that the oxidation rates of the glassy alloy are slower than those of pure Co, indicative of a better oxidation resistance. An exclusive scale of CoO was observed after the oxidation of the glassy alloy in the temperature range of interest, and several crystalline phases formed on the substrate beneath the scale, consisting of pure Co (both FCC and HCP structures), Co 3B, Co 2Si, CoFe, and Co 2B (absent at 450 °C), which indicated the occurrence of crystallization.

Optical, magnetic and electrical investigation of cobalt ferrite nanoparticles synthesized by co-precipitation route

Aluminum substituted cobalt ferrite nanoparticles CoFe 2− x Al x O 4 (for x = 0.00, 0.25, 0.50) have been synthesized by the chemical co-precipitation route. The average crystallite size was calculated using the Scherrer formula and found within 17–27 nm range. The optical absorption spectra of all the samples showed two clear electronic transitions, first is around 0.75 eV while the second at about 0.84 eV. The later is identified by means of 4A 2 → 4T 1 ( 4F) transition while the former is attributed to the overlapping of the 4A 2 → 4T 1 ( 4F) transition of the tetrahedral Co 2+ ions and the Co 2+ + Fe 3+ → Co 3+ + Fe 2+ metal–metal charge transfer transition. The saturation magnetization at room temperatures was found to be 61.50 emu/g for pure CoFe 2O 4 nanoparticles, while it decreased with increasing Al 3+ concentration up to 52.00 emu/g (for x = 0.50). The Curie temperature was determined from AC magnetic susceptibility measurement. It was observed that Curie temperature decreased with Al 3+ concentration ( x) and DC electrical resistivity decreased with increase in temperature. Activation energy and drift mobility have been calculated from the temperature dependent DC electrical resistivity measurements for all the samples. The variation of dielectric constant, dielectric loss and tangent loss factor for all the samples have been studied as a function of frequency in the range 600 Hz to 1 MHz at room temperature.

Synthesis and magnetic properties of CoFe 2O 4 nanoparticles confined within mesoporous silica

We report here the synthesis and magnetic properties of cobalt ferrite (CoFe 2O 4) nanoparticles inside the nanoscale channels of highly ordered mesoporous silica SBA-15. Formation of CoFe 2O 4 nanoparticles inside the mesoporous channels was realized by impregnation of cobalt salt and iron salt precursors into the channels of the SBA-15, followed by calcination at different temperatures (400–1000 °C) in air. The products were characterized by X-ray diffraction (XRD), field emission scanning and transmission electron microscopies (FESEM and TEM), and nitrogen adsorption–desorption isotherm measurements. As per results, a typical characteristic of the obtained materials is that the mesoporous channels of SBA-15 are partially filled by CoFe 2O 4 nanocrystallites. In consequence, these materials exhibit open, ordered 2D hexagonal frameworks, which are very similar to that of the pristine SBA-15 except for the reduced dimension and specific surface area. Magnetic properties of the obtained materials show strong dependence on the calcination temperature. The maximum-value combination of the saturation magnetization ( Ms), the remnant magnetization ( Mr) and the coercivity ( Hc) is obtained from the sample prepared at 1000 °C. Moreover, compared with the pure CoFe 2O 4 powder prepared at the same temperature, the CoFe 2O 4 incorporated SBA-15 composite possess higher magnetic parameters ( Ms, Mr and Hc).

A novel poly(o-anisidine)/CoFe 2O 4 multifunctional nanocomposite: Preparation, characterization and properties

A novel poly(o-anisidine) (POA)/CoFe 2O 4 nanocomposite was synthesized by a facile in situ polymerization of o-anisidine in the presence of CoFe 2O 4 nanoparticles which were obtained by a simple refluxing process in ethylene glycol. The structures of the resulting nanocomposite were investigated by means of X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra. The optical, thermal and magnetic properties of the POA/CoFe 2O 4 nanocomposite were characterized by UV–visible spectrometer, thermogravimetry analyzer (TGA) and vibrating sample magnetometer (VSM). It was indicated the existence of CoFe 2O 4 in the POA/CoFe 2O 4 nanocomposite. The scanning electron microscopy (SEM) observation illustrated that POA layers were wrapped on the surface of CoFe 2O 4 nanoparticles appearing as small aggregated globules. The POA/CoFe 2O 4 nanocomposite exhibited a ferromagnetic behavior under applied magnetic field at room temperature. The saturation magnetization of POA/CoFe 2O 4 nanocomposite was lower than that of pure CoFe 2O 4 nanoparticles due to the contribution of non-magnetic POA layers.

Magnetic CoFe 2O 4 nanocrystal: A novel and efficient heterogeneous catalyst for aerobic oxidation of cyclohexane

Magnetic nanocrystalline spinel-type cobalt ferrite complex oxides were prepared by a simple sol–gel auto-combustion method at five different molar ratios of Co II to Fe III (1:4.0, 1:2.8, 1:2.0, 1:1.5, and 1:1.1) and characterized by X-ray diffractometry (XRD), Fourier transform infrared spectrophotometry (FT-IR) and transmission electron microscopy (TEM). Their catalytic performance was evaluated in the oxidation of cyclohexane with oxygen as oxidant in the presence of neither solvents nor reducing agents. It has been revealed that the catalysts had high catalytic activities for heterogeneous oxidation of cyclohexane. Especially, when pure CoFe 2O 4 was used as catalyst; excellent results with turnover number of 288 and 92.4% selectivity for cyclohexanone and cyclohexanol was obtained under 1.6 MPa of initial oxygen pressure at 418 K after 6.0 h of reaction. The influences of initial oxygen pressure, reaction temperature, reaction time, and free-radical initiator on the oxidation of cyclohexane over CoFe 2O 4 were investigated. The catalyst can be easily separated by an external magnet and no obvious loss of activity was observed when reused in five consecutive runs. CoFe 2O 4 was proved to be also efficient for oxidation of linear alkanes.

Studies on redox H 2–CO 2 cycle on CoCr xFe 2− xO 4

Completely reduced CoCr xFe 2 − xO 4 can be used to decompose CO 2. It was found that for pure CoFe 2O 4 there is no FeO formation in the first step while there is formation in the second step. For CoCr 0.08Fe 2−0.08O 4, there is no FeO formed in all the oxidation process, because of effect of Cr 3+. Pure CoFe 2O 4 was destroyed at the first reaction cycle of H 2 reduction and CO 2 oxidation, while doped Cr 3+ spinel CoCr 0.08Fe 1.92O 4 showed good stability. The results from H 2-TG, CO 2-TG and XRD show that the addition of Cr 3+ to CoFe 2O 4 can inhibit the increasing of crystallite size and the sintering of alloy. Most importantly, the CoCr 0.08Fe 1.92O 4 can be used to decompose CO 2 repeatedly, implying that it is a potential catalyst for dealing with the CO 2 as a ‘green house effect’ gas.

Study on supercritical hydrothermal synthesis of CoFe 2O 4 nanoparticles

CoFe 2O 4 nanoparticles with diameter of about 5 nm were prepared at 390 °C by batch supercritical hydrothermal synthesis method. It was found that the characteristic of products depended on pH, temperature, mole ratio ( r) of Co 2+ to Fe 3+ and coexisting cations in reactant solutions. The reaction time and the coexisting cations (Na + and K +) had little effect on the size and morphology of CoFe 2O 4 particles. The products were a mixture of CoFe 2O 4 and Fe 2O 3 at r < 0.5 and Co 1+ x Fe 2− x O 4 (0 ≤ x ≤ 1) at r ≥ 0.5. Pure CoFe 2O 4 nanoparticles with uniform size were synthesized at 390 °C, pH 12 and r = 0.5. The maximum coercivity and saturation magnetization of CoFe 2O 4 prepared by the present method were 340.6 Oe and 68.9 emu/g, respectively. The mechanism for batch supercritical hydrothermal synthesis of CoFe 2O 4 nanoparticles is believed to be a homogeneous phase reaction of Co(NO 3) 2·6H 2O and Fe(NO 3) 3·9H 2O aqueous solution.

Coordination compounds containing urea as precursors for oxides—A new route of obtaining nanosized CoFe 2O 4

Pure CoFe 2O 4 particles with an average size in the range 38–57 Å and a surface area of 60–67 m 2 g −1 have been produced at a low temperature (450 °C) through thermal decomposition of polynuclear coordination compounds containing urea as ligand, with different metal:ligand molar ratios (Fe 3+:Co 2+:urea =2:1:6 and 2:1:8), synthesized by two routes (a precipative and a solid state one).

Pulsed laser deposition of cobalt ferrite in a reactive O 2:N 2 atmosphere: effect of the deposition pressure and temperature

Thin films of CoFe 2O 4 have been fabricated by pulsed laser ablation of a metallic CoFe 2 target at two different temperatures (200 and 400 °C) and in various O 2:N 2, 20:80 pressures [from 0.7 Pa (5×10 -3 Torr) up to 26.7 Pa (2×10 -1 Torr)]. Too low pressures resulted in an insufficient oxidation of the deposited material and an antiferromagnetic (Fe,Co)O phase is observed together with CoFe 2O 4. A minimum pressure of 6.7 Pa was found necessary to obtain pure CoFe 2O 4 films with magnetic properties close to the bulk. The higher the pressure and the temperature, the larger was the roughness of the films. The optimum deposition temperature and pressure to obtain flat (3 nm rms roughness) CoFe 2O 4 films were, respectively, 200 °C and 6.7 Pa.

Faraday rotation of pure and substituted cobalt ferrite single crystals

Faraday rotation measurements have been performed on single crystals of CoFe 2O 4, CoFe 2− x Al x O 4 ( x = 0.27) and Co 1− y Cd y Fe 2O 4 ( y = 0.25) at 1150 nm wavelength as a function of temperature (5⩽ T⩽580 K). The magnetic field up to 2 T was applied along two crystallographic orientations [100] and [111]. Results show a very strong anisotropy of magnetic origin due to Co 2+ and/or tetrahedral site occupancy. Crystal structure determinations show that Al 3+ substitution in pure CoFe 2O 4 increases the tetrahedral Co 2+ amount, leading to a strong decrease of the absolute FR.

Martensitic transformations in ultra-fine particles of metals and alloys

Abstract Martensitic transformations in ultra-fine particles of Fe-Ni alloys, pure Co and Co-Fe alloys have been studied by X-ray diffraction and electron microscopy. The diameter of the particles used in the present work is 20–200 nm, three orders of magnitude smaller than that of the particles employed so far in studies of the martensitic transformation of ‘fine particles’. The composition range of Fe-Ni alloys is 12–35 at.% Ni and that of Co-Fe is 3–6 at.% Fe, and most of the particles are defect-free single crystals in the as-formed state. The most surprising finding is that the transformation below room temperature is very difficult to induce by simple cooling even in the case where particles of the parent phase contain lattice defects, while the transformation above room temperature occurs normally in most of the particles of Fe-Ni alloys and deformation at room temperature can easily induce the transformation. For pure Co and Co-Fe alloys, the transformation products above room temperature are 2H a...