Substitution Of Cobalt For Iron Research Articles

Effect of Nd, Pr substitutional atoms on the magnetic and magnetostrictive properties in (Tb-Dy)(Fe-Co)2 Laves phases

Polycrystalline TbxDy1-xR0.1Fe2-zCoz (R = Nd, Pr, x = 0.2, 0.3; z = 0, 1.3) cubic Laves phase alloys with MgCu2-type structure were prepared by arc melting followed by homogenizing annealing. The crystal structure, magnetic properties, and magnetostriction have been investigated. Compounds with high values of magnetostrictive susceptibility were found in the temperature range 150-300 K. Compounds with partial substitution of cobalt for iron demonstrate a change in the sign of anisotropic magnetostriction. This work continues the search for magnetostrictive materials with inexpensive neodymium and praseodymium.

Magnetoresistive effect in the cobalt-doped bismuth ferrite films

Bismuth ferrite films have been synthesized by the burst-mode deposition of the BiFe0.8Co0.2O3 solid solutions onto object glasses. The surface morphology of the BiFe0.8Co0.2O3 films has been examined. The effect of electron doping implemented by substitution of cobalt for iron in the BiFe0.8Co0.2O3 films on their magnetic, electrical, and galvanomagnetic properties has been investigated at temperatures of 77‒600 K in magnetic fields of up to 12 kOe. The negative magnetoresistance has been observed, which changes its sign in the region of formation of magnetically heterogeneous states and attain its maximum value above room temperature. It has been established that the magnetoresistance is caused by the competition of electron hoppings and localization of electrons in a magnetic field. Using the Hall measurements, the carrier type has been determined. A model of the change in the curriers sign upon heating due to the shift of the chemical potential relative to the impurity subband has been proposed.

The effect of energy-dependent electron scattering on thermoelectric transport in novel topological semimetal CoSi

Cobalt monosilicide and its solid solutions with Fe or Ni crystallize in B20 cubic noncentrosymmetric structure. These compounds have long been known as promising thermoelectric materials. Recently it was revealed, that they also have unconventional electronic topology. This renewed interest to the investigation of their transport properties. In order to improve theoretical description of thermoelectric transport in these compounds, we take into account electron scattering beyond commonly used constant relaxation time approximation. Using first principle calculations, we investigate the scattering of charge carriers by phonons and point defects. The dependence of the scattering rate on the energy correlates with that for the total density of states. This implies that in this material not only the intraband, but also the interband scattering is important, especially for bands with low density of states. The Seebeck coefficient and the electrical resistivity of CoSi and of dilute solid solutions Co1−xMxSi (M = Fe or Ni, x < 0.1) are calculated as a function of temperature and the alloy composition. We show that the account of strong energy dependence of relaxation time is important for the description of experimentally observed rapid increase of the resistivity and qualitative change of its temperature dependence with the substitution of cobalt for iron, as well as for the description of the magnitude of the Seebeck coefficient, its temperature and composition dependence.

Phase equilibria, crystal structure at 1373 K and properties of complex oxides in the Nd–Co–Fe–O system

Phase equilibria in the Nd–Co–Fe–O system were systematically studied at 1373 K in air. The homogeneity range and crystal structure of solid solution NdCo1–xFexO3 (0.0 ≤ x ≤ 1.0) have been studied by the X-ray powder diffraction method. The structural parameters of complex oxides have been refined by the full-profile Rietveld method. It was shown that all oxides reveal practically stoichiometric oxygen composition within the entire temperature range under investigation. The values of thermal expansion coefficients for the cobaltites NdCo1–xFexO3 (x = 0.3, 0.7) have been calculated within the wide temperature range in air. Chemical stability of NdCo1–xFexO3 (x = 0.3, 0.7) in respect to the solid electrolyte materials (Ce0.8Sm0.2O2–δ and La0.88Sr0.12Ga0.82Mg0.18O3-δ) was examined. Electrical conductivity of NdCo1–xFexO3 (x = 0.3, 0.7) was measured as a function of temperature within the range 300–1373 K in air. It was shown that substitution of cobalt for iron leads to the decrease of conductivity. The isothermal-isobaric cross-section of the phase diagram for the Nd–Co–Fe–O system at 1373 K in air has been presented.

Characterization of magnetocaloric effect, magnetic ordering and electronic structure in the GdFe1−xCoxSi intermetallic compounds

GdFeSi silicide is a strong ferromagnet with Curie temperature (Tc) equal to 118 K. The substitution of cobalt for iron continuously suppresses ferromagnetism of the former compound, while it changes magnetic transition temperature nonlinearly. When the molar amount of cobalt reaches 0.4, the temperature of magnetic transition reaches minimal value i.e, 70 K. For larger amount of cobalt, magnetic transformation temperature rises well above 200 K and the antiferromagnetic interactions become dominant. In the present work we have found that the magnetic transformation temperature can be strictly correlated with the lattice constant c, which determines the distance between gadolinium layers as well as distance between neighboring gadolinium atoms in one layer. These results correspond to the change of amplitude of magnetocaloric effect which is being suppressed when the amount of cobalt increases. Adiabatic temperature change is equal to 2 K during the magnetic field cycle 0–1.7 T for pure GdFeSi, while no temperature change is observed during the same cycle for pure GdCoSi because of its antiferromagnetic character.

Effect of Substitution of Cobalt for Iron in Sr4Fe6O13−( on the Catalytic Activity for Methane Combustion

AbstractA series of mixed oxides Sr4Fe6−xCoxO13−δ (x=0, 1, 2, 3, or 4) were prepared by sol‐gel method and used for catalytic combustion of methane. The structural properties of oxides were characterized by XRD, TGA, and XPS. The layered intergrowth perovskite‐like oxide Sr4Fe5CoO13−δ exhibits the highest catalytic activity for methane combustion under the experimental conditions. The enhanced catalytic activity of Sr4Fe5CoO13−δ for methane combustion could be attributed to the increased amount of oxygen vacancy caused by the partial substitution of cobalt for iron in the Sr4Fe6O13, which was confirmed by TGA and XPS.

Structure, nonstoichiometry and thermal expansion of the NdBa(Co,Fe) 2O 5+δ layered perovskite

NdBaCo 2− x Fe x O 5+δ (0.0 ≤ x ≤ 2.0) series were prepared by a solid state reaction. Singe phase solid solutions were obtained within the range 0.0 ≤ x ≤ 1.4. The crystal structure of iron substituted solid solutions NdBaCo 2− x Fe x O 5 + δ was described within the tetragonal unit cell a p × a p × 2a p (S.G. P4/mmm). The substitution of cobalt for iron leads to the monotonous increase of the unit cell parameters and the unit cell volume. The values of the oxygen content in NdBaCo 2− x Fe x O 5 + δ ( x = 0; 0.2) as a function of temperature were determined by TGA. The thermal expansion measurements of NdBaCo 2− x Fe x O 5 + δ ( x = 0; 0.2; 0.4; 0.6 and 0.8) were performed. Chemical expansion constituent was separated.

Dicamba Monooxygenase: Structural Insights into a Dynamic Rieske Oxygenase that Catalyzes an Exocyclic Monooxygenation

Dicamba (2-methoxy-3,6-dichlorobenzoic acid) O-demethylase (DMO) is the terminal Rieske oxygenase of a three-component system that includes a ferredoxin and a reductase. It catalyzes the NADH-dependent oxidative demethylation of the broad leaf herbicide dicamba. DMO represents the first crystal structure of a Rieske non-heme iron oxygenase that performs an exocyclic monooxygenation, incorporating O 2 into a side-chain moiety and not a ring system. The structure reveals a 3-fold symmetric trimer (α 3) in the crystallographic asymmetric unit with similar arrangement of neighboring inter-subunit Rieske domain and non-heme iron site enabling electron transport consistent with other structurally characterized Rieske oxygenases. While the Rieske domain is similar, differences are observed in the catalytic domain, which is smaller in sequence length than those described previously, yet possessing an active-site cavity of larger volume when compared to oxygenases with larger substrates. Consistent with the amphipathic substrate, the active site is designed to interact with both the carboxylate and aromatic ring with both key polar and hydrophobic interactions observed. DMO structures were solved with and without substrate (dicamba), product (3,6-dichlorosalicylic acid), and either cobalt or iron in the non-heme iron site. The substitution of cobalt for iron revealed an uncommon mode of non-heme iron binding trapped by the non-catalytic Co 2+, which, we postulate, may be transiently present in the native enzyme during the catalytic cycle. Thus, we present four DMO structures with resolutions ranging from 1.95 to 2.2 Å, which, in sum, provide a snapshot of a dynamic enzyme where metal binding and substrate binding are coupled to observed structural changes in the non-heme iron and catalytic sites.

Increase in the magnetostrictive susceptibility of Tb0.3Dy0.67Ho0.03Fe2−x Co x alloys upon substitution of cobalt for iron

This paper reports on the results of investigations into the concentration dependences of the magnetostrictive susceptibility, the magnetostriction, the magnetization, and the Curie temperature for Tb0.3Dy0.67Ho0.03Fe2−x Co x alloys upon substitution of cobalt for iron. It is revealed that the temperature of the spin-reorientation transition shifts toward room temperature with an increase in the cobalt content in the range 0 ≤ x ≤ 1.3. Substitution of cobalt for iron in the alloys leads to a decrease in the contribution of the 3d transition metal sublattice to the magnetic anisotropy owing to the opposite signs of the single-ion anisotropy constants for iron and cobalt. The decrease observed in the magnetocrystalline anisotropy compensated in both rare-earth and 3d transition metal sublattices is responsible for the high magnetostrictive susceptibility of the studied compounds at a high cobalt content (x = 1.3) in the room-temperature range.

Structure and magnetic properties of Gd3(Fe0.665Co0.313Ti0.022)29

Abstract A new compound Gd 3 (Fe 0.665 Co 0.313 Ti 0.022 ) 29 with Nd 3 (Fe,Ti) 29 -type structure was synthesized. The crystal structure of Gd 3 (Fe 0.665 Co 0.313 Ti 0.022 ) 29 is refined by Rietveld analysis with a monoclinic lattice and a space group P2 1 /c derived from the CaCu 5 -type structure. The lattice constants a , b , c and the unit cell volume V are decreased by the substitution of cobalt for iron. The compound shows a high Curie temperature of 886 K and a planar anisotropy. The saturation magnetization of the compound is slightly higher than that of its parent compound Gd 3 (Fe 0.978 Ti 0.022 ) 29 .

Magnetic phases in quasi-binary (Fe1−x Cox)Ge2 intermetallic compounds

Magnetic neutron diffractometry revealed the existence in (Fe1−xCox)Ge2 solid solutions (x<0.5) with C16 structure of only two magnetic phases, namely, low-temperature (AFI) and high-temperature (AFII). A third magnetic phase, AFIII, suggested by earlier magnetic measurements, has not been found. The AFI and AFII phases have a commensurate and an incommensurate antiferromagnetic structure with the wave vectors k0=2π/a (1,0,0) and k=k0+δk, respectively. The regions of their existence are shown in the magnetic phase diagram. Neutron diffraction measurements yielded the concentration dependence of the average magnetic moment per atom in the antiferromagnetic sublattice of a 3d metal, which, similarly to the dependence of the Neel point on x, was found to be nonlinear. An analysis of these dependences suggests that substitution of cobalt for iron is accompanied, on the one hand, by a decrease of the local spin density on the iron atoms in the nearest environment of a cobalt atom and, on the other hand, by an increase of the effective exchange integral between the nearest-neighbor iron atoms located along the tetragonal axis.

Effect of hydrogen for the magnetic properties of iron and cobalt in PuNi3 type hydrides Y(Fe1−xCox)2.9Hy

Magnetization and Mössbauer measurements were performed for PuNi3 type alloys Y(Fe1−xCox)2.9 and their hydrides. The composition dependencies of magnetization, Curie temperature, and average hyperfine field of 57Fe in the alloys show a maximum near x=0.5, and those in hydrides decrease with increasing x. This behavior suggests that the magnetic moments of iron and cobalt are nearly the same, except for cobalt rich alloys. Numerical fitting using a Stoner theory with a parabolic band was performed. It was assumed that the alloys and hydrides are ferromagnets of 3d-band-hole with incomplete saturation. It was shown that both the exchange energy kθ and Fermi energy ε0 decrease with substitution of cobalt for iron, and that the difference in the composition dependencies of kθ/ε0 in alloys and hydrides leads to different composition dependencies of the magnetization and Curie temperature. It was shown that ε0 and kθ decrease with hydrogenation, but kθ/ε0 increases to lead magnetization increase only in YFe3.

Magnetic phase diagram of the DyFe 10 − xCo xV 2 system

The effect of the substitution of cobalt for iron in tetragonal DyFe 10 − x Co x V 2 alloys for 0 ⩽ x ⩽ 10 was studied by X-ray, magnetothermogravimetric and a.c. susceptibility techniques. From these results we present a phase diagram for the spin arrangement in the Dy(Fe,Co) 10V 2 system. A distinctive feature in this diagram is the observation that with the substitution of cobalt, the spin re-orientation (axial to cone) is found to shift to higher temperatures, while at the same time the (cone to plane) spin reorientation is suppressed to lower temperatures. This behaviour is in contrast to that observed in the Nd(Fe,Co) 10V 2 system.

Melt-spun Pr2(Fe1−xCox)14B permanent magnet materials

The substitution of cobalt for iron is known to increase the Curie temperature and stabilize the magnetic properties of melt-spun Nd2(Fe1−xCox)14B ribbons. The preparation of optimum permanent magnets from cobalt-substituted materials is, however, complicated by the need for nonstoichiometric starting materials which vary with the level of cobalt concentration. This paper contains the results of selecting compositions which optimize the room-temperature properties of melt-spun ribbons containing Pr2(Fe1−xCox)14B as the principal constituent. The hard magnetic properties of 11 cobalt concentrations were examined spanning the range x=0 to 1, inclusive. For cobalt concentrations up to x=0.5, the remanence and energy product did not change substantially from the x=0 values of 8 kG and 12 MGOe, respectively. Remanence and energy product decreased monotonically to their endpoint values of ∼5 kG and ∼5 MGOe for cobalt-rich alloys (x&amp;gt;0.5). The coercivity increased smoothly from 13 kOe for x=0 to 25 kOe for x=1. There was no evidence of the down turn in Hci normally associated with decreasing anisotropy.

NdFeB magnets with higher Curie temperature

Substitution of cobalt for iron increases the Curie temperature (T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> ) of NdFeB alloy but the anisotropy field (H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</inf> ) and the intrinsic coercivity force (H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ci</inf> ) was found to decrease rapidly [1]. Aluminum was found to be effective in increasing H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ci</inf> of NdFeCoB alloys. However, aluminum decreases the saturation magnetization (M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ) and T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> of these alloys. A systematic study of the effect of aluminum substitution on the magnetic properties of NdFeCoB system has been completed. Higher boron level is found necessary to stabilize the magnetic phases in NdFeCoAlB alloys. A NdFeCoAlB magnet with a T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> of 430°C, B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> of 9,300 Gauss, H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> of 9,100 Oe, H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ci</inf> of 18,000 Oe and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BH_{\max}</tex> of 21.6 MGOe was obtained. Nickel addition to the NdFeCoB system increases both M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> and T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> . Primary magnetic properties of NdFeCoMB, where M = Al or Ni, are also presented.

Mechanism of the control of dioxygen binding in a dimeric cobalt-substituted insect hemoglobin. Resonance Raman evidence for cobalt-axial-ligand bond changes.

Resonance Raman spectroscopy has been used to investigate the allosteric control mechanism for O2 binding in a cobalt-substituted dimeric insect hemoglobin (CTT II), which exhibits a large Bohr effect due to a pH-induced transition between two ligand affinity states. Substitution of cobalt for iron in CTT II does not modify the Bohr effect, but permits the resonance enhancement (hence the detection) of Raman lines corresponding to the vibrations of the axial ligand-cobalt bonds. Using 16O2/18O2 isotope substitution the O-O and Co-O2 stretching and the Co-O-O bending mode have been assigned to the two affinity states of this hemoglobin: v (O-O) changes from 1152 cm-1 (pH 5.5; t conformation) to about 1125 cm-1 (pH 9.5, r conformation), v (Co-O2) from 512 cm-1 (pH 5.5) to 537 cm-1 (pH 9.5) and delta (Co-O-O) from 378 cm-1 (pH 5.5) to 390 cm-1 (pH 9.5). The Co-N epsilon (His) stretching mode has also been detected changing from 313 cm-1 (pH 5.5) to 307 cm-1 (pH 9.5). For the first time, reciprocal behaviour between the Co-N epsilon and Co-O2 bonds and between the Co-O2 and the O-O bonds in an allosteric hemoglobin are demonstrated. Furthermore, the pH sensitivity of a vinyl bending mode in the range of 411-415 cm-1 has been investigated and shown also to reflect the t in equilibrium with r conformation transition.

Magnetic Properties and Crystal Structures of Nd-Fe-Co-B System Permanent Magnets

Several experimental studies have been carried out recently on the magnetic properties of Nd-Fe-B alloys. In this paper, we report on the effects of partial substitution of cobalt for iron in the Nd-Fe-B system. The samples prepared by powder metallurgical methods were of the composition Nd 23-y Fe 77-2x CO 2x By, where x = 0 to 10 and y = 5 to 10. We have obtained significant improvement in the Curie temperature by increasing the cobalt content in the alloy system. The temperature coefficient ?r of the Nd 16 Fe 66 Co 11 B 7 is about -0.02 percent/°C, in the temperature range 20 to 100°C, compared with -0.03 percent/°C for Nd-Fe-B samples. We developed a magnet in the Nd-Fe-Co-B system with a maximum energy product of 41 MGOe.

Nd-Fe-Co-B 系磁石の磁性と結晶組織

Several experimental studies recently have been carried out on magnetic properties for Nd-Fe-B alloys. In this paper, we report on the effects of partial substitution of cobalt for iron in the Nd-Fe-B system. The samples prepared by powder metallurgical method have composition Nd23-yFe77-2xCo2xBy, where x=0∼10, y = 5∼10. we have obtained significant improvement in the Curie temperature with increasing cobalt content in the alloy system. The temperature coefficient of σr of the Nd16Fe66Co11B7 is about -0.02%/°C, in the temperature range 20∼100°C compared with -0.03%/°C for the Nd-Fe-B samples. We have achieved a magnt with the maximum energy product of 41 MGOe in the Nd-Fe-Co-B system.

Structure of human deoxy cobalt haemoglobin

The structure of human adult deoxy cobalt haemoglobin has been compared to that of the native ferrous form by refinements based on X-ray data to 2.5 Å resolution. The two structures were refined in parallel by conventional methods and selected structural differences were measured by a novel difference refinement method applicable to closely related structures. The distance between the metal and the haem plane is 0.33 ± 0.08 Å in the cobalt derivative and 0.56 ± 0.03 Å in the native. The Co 2+HisF8N ϵ bond length is about 0.1 to 0.2 Å longer than the Fe 2+HisF8N ϵ bond length; the distance of N ϵ from the mean haem plane remains the same in the two structures and the substitution of cobalt for iron produces no significant change in globin structure. The free energy of co-operativity of cobalt haemoglobin is known to be about one-half of that of the native haemoglobin; the reason for this reduction is not evident from the structure of cobalt deoxyhaemoglobin.

Studies on cobalt myoglobins and hemoglobins: XIII. A consequence of the occurrence of glutamine at the E7 (58) site of α subunits in opossum hemoglobin

To investigate the mode of interactions between heme metal, bound oxygen and the distal residue at the E7 site, we have measured accurate oxygen equilibrium curves, oxygen binding relaxations following temperature-jump, and electron paramagnetic resonance spectra of natural and cobalt-substituted opossum hemoglobin, which has glutamine and histidine at the E7 site of the α chain and the β chain, respectively, and compared them with those of natural and cobalt-substituted human hemoglobin, which has histidine at the E7 site of both the α and β chains. Natural opossum hemoglobin has a lower oxygen affinity, slightly smaller and pH-dependent co-operativity, a somewhat greater Bohr effect, and a smaller effect of organic phosphates such as 2,3-diphosphoglycerate and inositol hexaphosphate on oxygen affinity as compared to natural human hemoglobin. Upon substitution of cobalt for iron, these oxygenation characteristics of opossum hemoglobin relative to those of human hemoglobin were preserved well. The behavior of the intrinsic oxygen association constants pertaining to the four oxygenation steps (i.e. the Adair constants) upon addition of the organic phosphates or pH changes indicates that the allosteric equilibrium in opossum hemoglobin is biased towards the T state as compared with that in human hemoglobin, and that the oxygen affinity of the R structure is lower for opossum hemoglobin than for human hemoglobin. The temperature-jump kinetic data indicate that the lower oxygen affinity of opossum cobalt-hemoglobin in comparison with that of human cobalt-hemoglobin can be ascribed to a decreased oxygen association rate constant. The electron paramagnetic resonance experiments on oxy and deoxy opossum and human cobalt-hemoglobins in buffered H 2O and 2H 2O, including their photolysed products at a low temperature, provided the following information. The cobaltous ion of the α subunits of deoxy opossum cobalt-hemoglobin is in an environment that is similar to that for cobaltous ions of deoxy human cobalt-hemoglobin in the T state. The hydrogen bond between the bound oxygen and the residue at E7, which has been shown to exist in oxy human cobalt-hemoglobin and oxy sperm whale cobalt-myoglobin, is absent or, at least, significantly altered in the α subunits of oxy opossum cobalt-hemoglobin, probably resulting in a lower oxygen affinity. Interference by isoleucine at E11α with an oxygen molecule is suggested as an explanation for the lowered affinity of opossum iron-hemoglobin. However, no straightforward structural explanation is available for the lower oxygen affinity of the R structure and the allosteric equilibrium biased towards the T state in opossum iron-hemoglobin.