Effect Of Cobalt Substitution Research Articles

Effect of cobalt substitution on magnetic properties of R2Fe17 silicides (R=Y, Gd, Tb, Er, and Tm)

Magnetic characteristics and unit-cell dimensions of the (off-stoichiometric) R2Fe17-type alloys based on R2Fe14−xCoxSi2, where R=Gd, Tb, Er, Tm, and Y and x=4 were determined. Partial substitution of Fe by Co slightly increases the saturation magnetization of the alloys and produces an average increase in the Curie temperature (Tc) of 55 K per Co atom. The enhancement of the Curie temperature with the addition of cobalt is attributed to the strengthening of the average 3d-3d exchange interaction. For Er- and Tm-containing compounds, replacement of Fe by Co has a remarkable effect in shifting the observed spin reorientation temperature toward higher temperatures. These results are discussed in terms of the influence of the interaction of the 4f electrons of the rare-earth ions with the 3d electrons of the transition-metal ions, which modifies the overall anisotropy of the alloys.

The effect of cobalt substitution on the annealing time of Nd-Fe-C ingot magnets

The effect of variable cobalt concentration and variable annealing times on the hard magnetic properties of Nd-Fe-C-type ingot magnets was studied. It was found that cobalt substitution can lead to a significant decrease in the annealing time needed to harden the ingots magnetically. A simple production route is described in which an isotropic ingot magnet is obtained after annealing for several hours with ( BH) max =70 kJ m −3, B r =0.63 T and J H c = 900 kA m −1.

Magnetic Properties of Sm-Fe-Co System Nitrided Compounds

Experiments were carried out to investigate the effect of cobalt substitution on the magnetic and physical properties of Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> nitrided compounds. Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> nitrided compounds (x=0 to 0.3) were prepared by heat treating fine powders of Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> alloys in N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas at a pressure of 4.9 MPa. X-ray diffraction patterns revealed these nitrided compounds to have a Th <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Zn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> -type structure. Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> alloys were observed to absorb the same large amount of nitrogen as Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> alloy. The Curie temperatures of these nitrided compounds increases with increasing Co content, and the lattice constants a and c decrease slightly. The intrinsic coercivity of 652.5 kA/m (8.20 kOe) and Curie temperature of 556°C were achieved for an Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</inf> Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.1</inf> compound.

Note on the effect of cobalt substitution on the hard magnetic properties of NdFeC ingot magnets

The effect of cobalt substitution on the hard magnetic properties of NdFeC-type ingot magnets was studied. It was found that cobalt substitution led to a significant decrease in the field strength needed to magnetize the ingot magnets. A simple production route is described which leads to an isotropic ingot magnet with ( BH max = 70 kJ m −3, B R = 0.65 T and JH c=800 kA m −1 . The temperature coefficient ( β=−0.6% K −1) of these magnets is the same as that of sintered NdFeB-type magnets.

Magnetic and structural properties of TbFe 10.8-xCo xW 1.2 alloys

A series of new alloys of composition TbFe 10.5Co ξW 1.2(0⩽ x ⩽10.8) has been synthesized and studied for their hard magnetic properties over the temperature range 4.2–1200 K. It is found that all compounds with x ⩽ 5 crystallize in a tetragonal structure of the ThMn 19 type. At higher cobalt content, i.e. x ⩽ 5, a considerable amount of an extraneous phase of the rhombohedral Th 2Zn 27 structure is observed. These compounds exhibit planar anisotropy for ξ ⩽ 5 at room temperature. Above room temperature the plane-tocone-type spin reorientation is found for this system. The Curie temperature T c of these materials is considerably enhanced by cobalt substitution and ranges from 560 K (TbFe 0.8W 1.2) to 1003 K (TbFe 5.8Co 5W 1.2). The effect of cobalt substitution on the anisotropic behaviour in the Tb (Fe, Co) 10.8W 1.2system is analysed.

High-resolution transmission electron microscope study of effects of cobalt substitution on the stability and perfection of YBa 2Cu 4O y superconductors

A small amount of Co is doped in the starting mixtures for preparing YBa 2Cu 4O y (1-2-4) type of superconductors and the resultant materials are examined by HRTEM, in order to examine the effects of Co substitution on the structural stability and perfections of the 1-2-4 structure. Up to about 2% substitution, the 1-2-4 phase is obtained as the major phase. The stability of (CuO) 2 double-chains (D), however, decreases gradually with further substitutions and partial conversions of double-chains into (CuO) single-chains (S) are induced. With 3% substitution, domains of the 2-4-7 structure with (D S D S D) sequences are formed together with those of the 1-2-4 one with a (D D D D) sequence. Small domains of a new ordered structure (D D S D D S D D S) are also observed in Co 3% specimen, suggesting the existence of a new Y 3Ba 6 (Cu, Co) 11O y (3-6-11) phase. The stability of the 2-4-7 phase increases by further substitution and, finally, it becomes the major phase at a 5% substitution by Co.

Hard magnetic properties of melt-spun Nd-Co-Fe-B materials

The effects of cobalt substitution on the hard magnetic properties of melt-spun neodymium-iron-boron materials are reported. Samples having the starting composition Nd0.135[(CoxFe1−x)0.95B0.05 ]0.865 with x=0, 0.05, 0.10, 0.15, 0.20, 0.35, 0.50, 0.75, and 1 were prepared by melt-spinning over a range of substrate surface velocities (i.e., quench rates) and their room-temperature magnetization characteristics measured. Choosing samples having maximal energy products, it was found that in the 0≤x≤0.5 interval the coercivity and remanence show modest overall diminution with x while the energy product declines more rapidly. Above x=0.5, the remanence, energy product, and especially the coercivity, severely deteriorate. X-ray diffraction studies indicate that for x&amp;gt;0.5 formation of the Nd2Fe14B-type structure is suppressed, and the samples contain progressively greater amounts of Nd2(Co,Fe)17.

Spin reorientations in R 2Fe 14- xCo xB systems (R = Pr, Nd and Er)

The effect of cobalt substitution on spin reorientation phenomena in R 2Fe 14- x Co x B systems (R = Pr, Nd, Er) was studied by means of bulk magnetometry in the temperature range 4.2–1100 K. It was established that in the Nd-based system the introduction of cobalt resulted not only in a shift of the low temperature spin reorientation (cone to axis) but also triggered, for x ⩾ 10, an appearance of a second spin reorientation (axis to plane) at high temperature. In the Pr-based system, for x ⩾ 9.5, a high temperature spin reorientation (axis to plane) was also observed. Its dependence on Co content was determined. For the Er-based system, an increase of the spin reorientation temperature (plane to axis) was observed as more cobalt was introduced into that system. It was also established that the tetragonal single-phase materials in this system exist only up to x = 5. Temperature-composition diagrams are presented, indicating types of spin arrangements observed in the investigated systems.

Leucine aminopeptidase (bovine lens). The relative binding of cobalt and zinc to leucine aminopeptidase and the effect of cobalt substitution on specific activity.

Prolonged incubation of zinc-zinc leucine aminopeptidase (bovine lens) (EC 3.4.1.1) with 0.05 M CoCl2 and M KCl in 0.2 M N-ethylmorpholine-HCl at pH 7.5 and 37 degrees yields an active enzyme in which 2 g atoms of Co2+ per 54,000 dalton subunit have replaced the Zn2+. Incubation of cobalt-cobalt leucine aminopeptidase with various AnCl2 concentrations or zinc-zinc leucine aminopeptidase with various CoCl2 concentrations in M KCl and 0.2 M N-ethylmorpholine-HCl at pH 7.5 and 37 degrees demonstrates that Co2+ and Zn2+ compete reversibly for two independent binding sites per subunit for which the ratio of the association constants for Zn2+ and Co2+ (1KZn:1KCo = 1KZn/Co; 2KZn:2KCo = 2KZn/Co) are 115 and 15.9 for sites 1 and 2, respectively. The specific activities of the various species of enzyme with 2 mM L-leucine p-nitroanilide as substrate in 0.2 M N-ethylmorpholine-HCl and 0.01 M NaHCO3 at pH 7.5 are estimated to be (in micromoles per min per mg) 0.043 for the zinc-zinc. 0.039 for the zinc-cobalt, 0.541 for the cobalt-zinc, and 0.536 for the cobalt-cobalt forms, which implies that activity is affected only when cobalt is substituted at site 1, the "activation site." The site, at which cobalt substitution has no effect on activity, is designated the "structural site." The value of Km for cobalt-cobalt leucine aminopeptidase with L-leucine p-nitroanilide as substrate in 0.2 M N-ethylmorpholine-HCl at pH 7.5 containing 0.01 M NaHCO3 at 30 degrees is 0.52 mM while Vmax is 0.90 mumol per min per mg. In the additional presence of 1 M KCl, Km is 0.19 mM while Vmax is 0.68 mumol per min per mg.

The effect of cobalt substitution on electrical conduction in nickel ferrite

Measurements are reported of the electrical resistivity of nickel ferrites having cobalt substitutions of up to 5%. For certain compositions large resistivities are found due to the buffering action of the cobalt ions, which behave in this respect similarly to managanese ions in nickel ferrite. Some differences are observed between cobalt- and manganese-doped materials and these are explained on the assumption that, although Co2+ ions may be readily substituted for Ni2+ ions, there exists a limiting concentration to which cobalt can replace iron in the ferrite lattice. Magnetization measurements are found to be in good agreement with this hypothesis.

Ferromagnetic Resonance in Garnet Y3Fe5-xCox/2Gex/2O12

The substitution of a small amount of Co 2+ and Ge 4+ for Fe 3+ in yttrium iron garnet causes remarkable changes of the magnetic anisotropy constants and Δ H . The magnetic anisotropy constants K 1 and K 2 of Y 3 Fe 5- x Co x /2 Ge x /2 O 12 depend strongly on temperature, and K 1 is linear to the concentration of cobalt at a given temperature, where x =0, 0.0042, 0.017, 0.048. The effect of cobalt substitution is similar to the case of magnetite containing cobalt, and can be accounted for by Slonczewski's theory with the value of the parameter |αλ|=100 cm -1 . The line width Δ H increases with the increase in cobalt concentration.