Magnetic Moment Of Cobalt Atoms Research Articles

Magnetic susceptibility and NEXAFS, EPR spectra of co-doped Bi3NbO7

The methods of NEXAFS, EPR spectroscopy and static magnetic susceptibility were used to analyze the condition and nature of exchange interaction of paramagnetic cobalt atoms within the bismuth niobate Bi3NbO7 matrix. The samples of Bi3Nb1-xCoxO7-δ with cubic fluorite-like structure were synthesized by the solid-phase method; their microstructure and magnetic properties were studied. The samples had monolithic, non-porous solid microstructure without clear crystal boundaries. The results of the magnetic susceptibility and NEXAFS studies showed that cobalt atoms in the solid solutions were predominantly represented by Co(II) and Co(III) high-spin atoms and their exchange-coupled aggregates with the antiferromagnetic type of exchange. The magnetic moment of cobalt atoms in the solid solutions exceeded the pure spin values for Co(II)s=3/2 and Co(III)s=2, and ranged from 6.12 to 7.15 μB. The analysis of the NEXAFS Co2p-spectra of the cobalt-doped solid solutions and cobalt oxides revealed that the studied Co atoms were mainly in the +3 and +2 oxidation states. Only one component was reliably established in the recorded EPR spectra. This was an asymmetric broad band with the g factor of about 4. This signal could be attributed to the high-spin state (S = 3/2) of Co(II).

Coexistence of Perpendicular and Parallel Exchange Bias Effects on Ni/CoO Bilayer

We present exchange bias properties of Ni/CoO bilayer field cooled in parallel and perpendicular directions. Magnetic moments of cobalt atoms in CoO magnetic unit cells are known to be slightly tilted with respect to their easy axes. Coexistence of both is attributed to the tilt of magnetic moments. CoO layer thickness was kept constant in this study, whereas Ni thickness was varied in a range in order to adjust its perpendicular magnetization. MOKE and VSM were exploited to determine their magnetic characteristics. After field cooling, Ni(22 A)/CoO(20 A) bilayer exhibited a large exchange bias of 3 kOe in parallel direction and a relatively small (0.5 kOe) in perpendicular direction at 10 K.

Synthesis, crystal and magnetic structure of a novel brownmillerite-type compound Ca 2Co 1.6Ga 0.4O 5

The novel compound Ca 2Co 1.6Ga 0.4O 5 with brownmillerite (BM) structure has been prepared from citrates at 950 °C. The crystal structure of Ca 2Co 1.6Ga 0.4O 5 was refined, from neutron powder diffraction (NPD) data, in space group Pnma , a = 5.3022 ( 6 ) Å , b = 14.884 ( 2 ) Å , c = 5.5276 ( 6 ) Å , χ 2 = 1.798 , R F 2 = 0.0455 , R wp = 0.0378 and R p = 0.0292 . On the basis of the NPD refinement the compound was found to be a G-type antiferromagnet (space group P n ′ m ′ a ) at room temperature, with the magnetic moments of cobalt atoms directed along chains of tetrahedra in the BM structure. Electron diffraction and electron microscopy studies revealed disorder in the crystallites, which can be interpreted as the presence of slabs with BM-type structure of Pnma and I 2 mb symmetry.

NMR evidence of metal-support interaction in syngas conversion catalyst Co-TiO2

To examine the relation between catalytic and magnetic properties, the zero-field NMR spectra and hysteresis loops of cobalt supported on silica, alumina, magnesia, titania, and ZSM-5 with and without the promoter thoria were investigated. Cobalt was incorporated on the support by simple physical admixture of precipitated cobalt and support, and by aqueous impregnation technique. Our studies indicate that the particle sizes are consistently lower in the presence of thoria. Of all the catalysts examined, the Co/Th/TiO2 catalyst exhibits a high saturation magnetization value—about 20% higher than pure cobalt. In addition, the NMR spectrum of the aqueous impregnation Co/TiO2 catalyst is distinctly different from the rest. All the NMR lines are shifted to a higher frequency by about 4 MHz. These two features—enhancement of the magnetic moment of cobalt atoms and increases in the hyperfine field at the Co nucleus—clearly indicate that there occurs strong metal-support interaction between cobalt and titania support. The higher hydrocarbon yields observed by the earlier investigators with Co/TiO2 catalysts might be related to this phenomenon.

THE MAGNETIC PROPERTY OF AMORPHOUS Pr-Co THIN FILMS

Amorphous thin films of PrxCo1-x alloys were prepared over the composition range 0.06-0.86 by the vacuum evaporation method with two sources. The magnetic properties of those films were measured by using extracting sample magnetometer, vibrating sample magnetometer and the alternating susceptibility set. The dependence of magnetization of these films on temperature and field were studied. It was found that the magnetization has a sudden drop near the temperature corresponding to the maximun of the value of the alternating magnetic susceptibility, and for samples with xco and Pr atom μpr were calculated. The effective magnetic moment of Co atom μco equals l.36f(x), where f(x) is the probability for bearing magnetic moment of cobalt atoms. The effective magnetic moment of Pr atom equals 1.6 μB in. the composition range 0-40% and decreases rapidly in the range 0.4-0.86.

Low temperature magnetic properties of NdxCo1− x amorphous thin films

Amorphous thin films of Nd x Co 1− x alloys were prepared over the composition range 0.07 ⩽ x ⩽ 0.96 by the vacuum evaporation method with two heating sources. The field dependence of magnetization σ( H) in 0–7 T and at 1.5 K for all samples were investigated. The magnetic structure of these films were studied by magnetic measurement. It was found that the effective magnetic moment of the Co atom μ Co = 1.87 ƒ(x)μ B, ƒ(x) being the probability for bearing magnetic moment of cobalt atoms, the effective magnetic moment of the Nd atom μ Nd = 2.28μ B for 0.07 ⩽ x ⩽ 0.50, and μ Nd = 2.28 - 1.76 (x − 0.50) for 0.50 ⩽ x ⩽ 0.96, and the maximum distribution angle ψ O of magnetic moment of neodymium atoms is about 66° at x < 0.50 and ψ O = 66° + 63.3° ( x − 0.50) at x ⩾ 0.50. The temperature dependence of the magnetization σ( T) at 1.5−200 K with H = 7.0 T has been measured. When the neodymium concentration is larger than 24 at %, there is a sudden drop of σ( T) at about 20 K, and this temperature does not change with increase of Nd component. The results show that the demagnetized state of the amorphous Nd-Co films may be composed of asperomagnetic and speromagnetic structures. The sudden drop of σ( T) near 20 K for samples with x ⩾ 0.24 may be explained by the phase transition between speromagnetism and paramagnetism.

On the magnetic properties of Y(Fe xCo 1- x) 2 compounds

The composition dependence of the mean magnetic moment of cobalt atoms in Y(Fe x Co 1- x ) 2 compounds is analysed in the local environment model. Cobalt has a magnetic moment of 1.56 μ B if there are at least two Fe atoms as nearest neighbours. The maximum in the composition dependence of the transition metal moments is due to the magnetic contributions of iron atoms only. The thermal variation of reciprocal susceptibility obeys a Curie-Weiss behaviour, in addition to the Pauli paramagnetic term. Finally, the influence of the variable magnetic interactions on the transition metal moments is discussed.

On the magnetic properties of Y(Fe xCo 1−x) 2 compounds

The composition dependence of the mean magnetic moment of cobalt atoms in Y(Fe xCo 1−x) 2 compounds is analysed in the local environment model. Cobalt has a magnetic moment of 1.56 μβ if there are least two Fe atoms as nearest neighbours. The maximum in the composition dependence of the transition metal moments is due to the magnetic contributions of iron atoms only. The thermal variation of reciprocal susceptibility obeys a Curie-Weiss behaviour, in addition to the Pauli paramagnetic term. Finally, the influence of the variable magnetic interactions on the transition metal moments is discussed.

Mossbauer study of the intermetallic compounds (Fe1-xCox)2B and (Fe1-xCox)B

Results of Mossbauer measurements on the intermetallic compounds (Fe1-xCox)2B(0<or=x<1) and (Fe1-xCox)B(0<or=x<or=0.5) are presented; the hyperfine field isomer shift and quadrupole splitting being measured as a function of composition and temperature between 80K and 1100K. The data indicate that the electron states at iron sites are well localized, and that iron keeps a nearly constant moment through the two ternary compound series. Moreover in (Fe1-xCox)2B the nonlinearity of the magnetization against concentration is attributed to an important change in the magnetic moments of cobalt atoms; the concentration and temperature dependence of the easy magnetization direction were also investigated.