Dependence of Magnetic Properties on Composition of Nanocrystalline Fe–M–B–Cu (M: Zr,Nb, Mo,Ti, Ta) Alloys

The specialized rf-Mössbauer technique is used to elucidate the magnetic properties of NANOPERM-type nanocrystalline alloys. The influence of alloy composition on the soft magnetic properties is studied for the Fe₈₀M₇B₁₂Cu₁ (M: Ti, Ta, Nb, Mo, Zr) alloys. The rf-Mössbauer experiments allowed us to distinguish magnetically soft nanoclusters from magnetically harder microcrystalline phases. The measurements performed as a function of the rf field intensity allowed the determination of the distribution of anisotropy fields related to the size distribution of bcc nanoclusters. Smaller anisotropy fields in the nanocrystalline phase were found in Nb-, Zr-, and Mo-containing alloys as compared with the alloys which contain Ti and Ta. The Mössbauer measurements were supplemented by X-ray diffraction determination of the size of nanocrystalline grains.     

Energy levels of 92Nb and 94Tc from 92Zr, 94Mo(p,nγ)92Nb, 94Tc

The γ-decays of the energy levels of ⁹²Nb and ⁹⁴Tc were measured following the ⁹²Zr(p, n)⁹²Nb and ⁹⁴Mo(p, n)⁹⁴Tc reactions. For ⁹²Nb the γ-ray thresholds were measured and a detailed excitation function was obtained near the ⁹³Zr ground-state isobaric analog resonance. Also, γ-γ coincidence measurements with two Ge(Li) detectors were made for both ⁹²Nb and ⁹⁴Tc. The coincidence measurements determined ten energy levels in ⁹²Nb and two levels in ⁹⁴Tc. A comparison with particle transfer reactions is used to elucidate the structure of ⁹²Nb levels observed here but not seen in the transfer reactions.     

固态六羰基钼的FT-拉曼光谱研究

固态六羰基钼的ＦＴ┐拉曼光谱研究李淑玲（地矿部岩矿技术研究所北京１０００３７）任玲（北京理工大学化学与材料学院北京１０００８１）ＦＴ┐ＲａｍａｎＳｐｅｃｔｒａｏｆＳｏｌｉｄＭｏ（ＣＯ）６ＬｉＳｈｕｌｉｎｇ（ＩｎｓｔｉｔｕｔｅｏｆＲｏｃｋａｎｄＭｉｎｅ...     

Promising half-metallic ferromagnetism in double perovskites Ba2VTO6 (T=Nb and Mo): Ab-initio LMTO-ASA investigations

The electronic and magnetic properties of new ordered vanadium-based double perovskite oxides Ba₂VTO₆ (T=Nb and Mo) have been investigated using the ab-initio linear muffin-tin orbitals method with the atomic-sphere approximation (LMTO-ASA). The calculations performed by using the local spin-density approximation with on-site Coulomb interaction (LSDA+U) style. The self-consistent band structure calculations predict half-metallic ferromagnetic (HM-FM) ground states with total spin magnetic moments of 2.1021 μ_B and 3.0633 μ_B per formula unit cell for Ba₂VNbO₆ and Ba₂VMoO₆, respectively. HM-FM nature in two compounds organizes from the ddpπ-superexchange interactions 3d-t_2g²–O (2p)–4d-t_2gⁿ (n=0 or 1), conformity with Zener–Goodenough–Kanamori rules.     

Spin-resolved NEXAFS from resonant X-ray scattering (RXS): Application to MnO

Resonantly excited metal K core line spectra of NiO, MnO, CuO and other compounds have been investigated at the beamlines X21 (NSLS/BNL), BW1 and W1.1 (HASYLAB/DESY). A novel technique for quantitative resolution of NEXAFS spectra into spin-up and spin-down components has been developed. Since the method employs spin conservation and local spin references, it needs no circularly polarized radiation and no sample magnetization for taking both the RXS and NEXAFS spectra. Hence antiferromagnetic and paramagnetic materials can be investigated as well.By utilizing linear dichroism with angular-dependent measurements on single-crystal samples, additional resolution of NEXAFS spectra is possible with respect to the orbital symmetry. Application of the method to paramagnetic MnO, for the first time, provides new and unambiguous experimental results confirming modern (LSDA+U) calculations. Received: 29 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

Zn_（1－x）Mg_xS_ySe_（1－y）四元半导体合金的拉曼散射光谱研究

用分子束外延方法在ＧａＡｓ（１００）衬底上生长了Ｚｎ１－ｘＭｇｘＳｙＳｅ１－ｙ四元半导体合金薄膜．用Ｘ－射线衍射方法确定了外延层的结构和晶格常数．测量了这些样品在平行和垂直两种不同几何配置下的拉曼散射光谱并对其特性做了研究。从实验上观察到了四类不同的晶格振动模：类ＺｎＳｅ的ＴＯ和ＬＯ模以及类ＺｎＳ和类ＭｇＳ的ＬＯ模，实验发现：在ＺｎＳｅ和ＺｎＳＳｅ中加入Ｍｇ使得类ＺｎＳｅ的ＴＯ和ＬＯ模的振动频率下降；同时，也使类ＺｎＳ模的频率随Ｓ的增加率减小。     

Desorption of halogens from Nb,Mo, Ta and W polycrystalline surfaces

The desorption kinetics of halogens from Nb, Ta, Mo and W polycrystalline surfaces are studied, at low coverage (Θ ? 10^?2 of a monolayer) and high temperature (1800–2400 K), using a pulsed ionic beam method. For a relatively high energy incident positive ion beam (? = 2500 eV), the diffusion kinetics of implanted Br and I ions towards the surface are observed. At low energy (? < 500 eV), a first order kinetic corresponding to the desorption of halogens from these surfaces is found. Preliminary results are given on the desorption energy and the preexponential factor of halogens adsorbed on Nb, Mo, Ta and W polycrystalline surfaces. The main result of this systematic study is that the mean adsorption lifetime for a given temperature, as the desorption energy decreases for F through I on all of the studied surfaces. A similarity between Nb and Ta, as between Mo and W surfaces for the desorption energies of halogens is also found.     

NEXAFS from adsorbed molecules: Ethanol and ethoxy on Cu(110)

NEXAFS studies above the O K-edge show that ethoxy can only be formed coexistent with ethanol on Cu(110) surfaces; in this state the O-C bond of ethanol is essentially parallel to the surface (to within ∼20°) but in ethoxy this bond is tilted from the surface normal by a much smaller amount (−35° ±15°). A marked line-shape difference is seen in the NEXAFS from the two species. The possible influence of substrate scattering on this line shape is discussed.     

Oscillatory behavior of the resistance of three-layer heteroepitaxial Mo/Nb/Mo (001) films

Electrical resistance of a three-layer heteroepitaxial Mo(35 nm)/Nb(d _Nb)/Mo(35 nm) (001) film was found to exhibit oscillatory behavior as a function of thickness d _Nb of the ultrathin Nb interlayer. The oscillation period is equal to one Nb monolayer (0.16 nm). The resistance minimum of such a film corresponds to the interlayer thickness with a half-completed monolayer and is equal to the resistance of an individual Mo film of thickness 70 nm equivalent to the total thickness of the three-layer film. In this case, the three-layer film conducts as if it is a unified layer. The resistance of a three-layer film with completed Nb monolayers is maximum and equal to the resistance of two individual parallel-connected Mo films of half thickness (35 nm) each. These results are explained by the strong influence of the built-in potential, whose magnitude and scattering properties are periodic functions of the interlayer thickness.     

Specific heat,cell parameters,phase T - p diagram,and permittivity of cryolite (NH 4 ) 3 Nb(O 2 ) 2 F 4

The temperature dependences of the specific heat, unit cell parameters, susceptibility to hydrostatic pressure, and permittivity of cryolite (NH₄)₃Nb(O₂)₂F₄ have been studied. Phase transitions of nonferroelectric nature have been detected. Entropy parameters point to the relation of structure distortions to ordering processes.     

Energy levels in 93Mo populated by the 93Nb(p,nγ) reaction

Energy levels of ⁹³Mo have been investigated by means of the ⁹³Nb(p, nγ)⁹³Mo reaction. The excitation functions of the level de-excitation γ-rays were measured with a Ge(Li) detector under proton bombardment in the energy range 3.0 to 5.0 Me V. A detailed γ-ray decay scheme which includes 69 levels and 123 γ-ray lines was constructed from the threshold energies for 64 γ-rays and the γ-ray excitation functions around five isobaric analogue resonances in the ⁹³Nb(p, nγ) reaction. Spin-parity values for 59 levels and favourable values for 8 levels were assigned from the analysis of relative neutron yields via the isobaric analogue resonances of the parent odd-odd nucleus ⁹⁴Nb. The results of the present experiment are compared with shell-model calculations.     

Ex-situ prepared films of 4-aminothiophenol on Au(1 1 1): photoemission, NEXAFS and STM measurements

Ex-situ prepared films of 4-aminothiophenol (4-ATP) on Au(1 1 1) have been studied by core-level photoemission using synchrotron radiation, ultra-high-vacuum scanning tunneling microscopy and spectroscopy (UHV-STM, STS), and X-ray absorption (NEXAFS). Photoemission measurements suggest that the film contains a relatively low percentage of 4-ATP bonded to the Au surface, with the presence of free 4-ATP, with oxidised and possibly dimerised molecules also present. We find a lower oxide content than has previously been observed, with well-resolved STM images. These images show a disruption of the long range order of the Au(1 1 1)-(22 × √3) reconstruction, with local nucleation of the reconstruction apparently induced by the 4-ATP, and bias-dependent contrast images. This latter effect, together with the asymmetry observed in STS, is ascribed to the presence of oriented molecular dipole layers between the metal and the organic material. NEXAFS data suggest a broadly upright geometry, with, however, considerable uncertainties.     

4s-4p transitions including intercombination lines in Zn-like Zr XI,Nb XII and Mo XIII

Energy levels of the configurations 4s4p and 4p² in zink-like Zr, Nb and Mo have been derived through the identification of spectral lines emitted from laser-produced plasmas. Intercombination lines in the 4s4p-4p² transition connect the singlet and triplet systems. Wavelengths for spinforbidden and magnetic quadrupole ground term combinations have been derived from the energy levels.     

Infrared Spectra of trans-nitrobis (2, 4-pentanediono) Aniline-Cobalt(III) Complexes

The infrared spectra of eighteen complexes of general formula trans-[Co(NO₂) (acac)₂ (R-C₆H₄NH₂)] (acac = acetylacetonate anion, R = 3- or 4-aniline substituent) are discussed. ¹⁵N-Labelling of the complexes containing aniline and p-toluidine yields assignments of the N-H, C-N and Co-N stretching frequencies and the N-H bending frequencies. These assignments receive support from the observed frequency shifts induced by varying the substituent R which also permits the assignment of the Co-o stretching frequencies.     

Desorption of halogens from some Nb,Mo, Ta and W single crystal surfaces

A systematic investigation of the thermal desorption of halogens from well characterized (111), (100) and (110) 4d (Nb, Mo) and 5d (Ta, W) transition metal surfaces has been carried out under low coverage conditions (θ < 10^?2 of a monolayer). Characterization of the surfaces was achieved by LEED, AES and work function determinations while the desorption kinetics were recorded in a large temperature range (1700–2300 K) using a pulsed ionic beam method. The new data concerning some Ta and W surfaces are presented and the results of this systematic study are discussed. It is shown that the halogen desorption parameters, e.g., desorption energies and preexponential factors, are independent of both surface structure and d bond filling of the substrate; E(F) ～4.75 eV, E(Cl) ～4.1 eV, E(Br) ～3.7 eV and τ₀ ～10^?13 ?10^?14 S. The halogen behaviour is compared with that of other adsorbates and with the predictions of a general chemisorption model.     

Spectra of K4Ru(CN)6

Luminescence of complex ions is a general phenomenon; the number of such complexes in various electronic configurations found to show emission is increasing rapidly. For some it has been possible to assign the emission as phosphorescence or as fluorescence, for others the proper assignment is as yet not clear.     

Solid-phase reactions between (100) GaAs and thin-film refractory metals (Ti,Zr, V,Nb, Cr,Mo, and W)

Recently, there has been an increased interest in the applications of refractory metals as gate materials for the self aligned gate process in the fabrications of GaAs field effect transistors. In this study, we systematically investigated the thermally induced interface interactions between (100) GaAs substrates and thin films of refractory metals (Ti, Zr, V, Nb, Cr, Mo, and W). Depth profilings of the M/GaAs interfaces were obtained using conventional and heavy ion Rutherford backscattering spectrometry. Phase identifications were achieved by x-ray diffraction.Results on the phase formation sequence, reaction kinetics, the distribution, composition and structure of the reacted phases and the interface reactivity of these contacts will be presented. Correlations between metal properties (electronegativity and metal-metal bond strength) and kinetics of the reactions (activation energy and reactivity of the interfaces) will also be discussed.     

Atomic displacements in dilute alloys of Cr, Nb and Mo

Kanzaki lattice static method is used to calculate the atomic displacements due to substitutional impurities in 3d (Cr) and 4d (Nb, Mo) metals. Wills and Harrison interatomic potential is used to calculate dynamical matrix and the impurity-induced forces up to second nearest neighbors. The calculated atomic displacements for 3d, 4d and 5d impurities in Cr (V, Mn, Fe, Ni, Nb, Mo, Ta and W), Nb (V, Cr, Mn, Fe, Zr, Mo, Ta and W) and Mo (V, Cr, Mn, Fe, Zr, Nb, Ta and W) are tabulated up to 10 NN’s. The strain field due to 3d impurities is least in Cr metal while it is larger in Nb and Mo metals. For 4d and 5d impurities the strain is larger in Cr metal than in Nb and Mo hosts. Similar trend is found for relaxation energies also.     

On the formation of the nanostructure in Fe80M7B12Cu1 (M: Ti, Ta, Nb, Mo) alloys

The dependence of the formation of the nanocrystalline bcc-Fe phase on the alloy composition is studied for Fe₈₀M₇B₁₂Cu₁ (M: Ti, Ta, Nb, Mo) alloys. The rf-Mössbauer technique is used to determine the optimal soft magnetic properties. This technique allowed us to compare anisotropy fields in each phase present in the composite alloys. The smallest anisotropy field was found in the bcc-Fe nanograins formed in Nb- and Mo-containing alloys.