共查询到20条相似文献,搜索用时 187 毫秒
1.
Guy H. Hayes Joseph I. Budnick Douglas M. Pease William A. Hines Myung H. Choi Steve M. Heald Dale E. Sayers 《Journal of magnetism and magnetic materials》1989,80(2-3):371-378
Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) studies of the transition metal sites in Metglas 2605 CO (Fe67Co18B14Si1) illustrate differences in the two sites. The average transition metal distance, obtained by standard EXAFS analysis, is larger for iron than for cobalt sites in this material. The XANES for Co and Fe are nearly identical except for a shift of the Co fine structure to high energy relative to that of Fe; the sign and magnitude of this shift is commensurate with the EXAFS results. Finally, there was no detected polarization dependence of the EXAFS, indicating that the structural manifestations of the magnetic anisotropy in this material are smaller than the detection limits of these experiments. 相似文献
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P. Zaleski K. SzymańskiW. Olszewski M. BiernackaK. Perzyńska D. Satu?aA. Go J. Przewo?nikD.A. Zaj?c M. PylakL. Dobrzyński 《Physica B: Condensed Matter》2011,406(17):3196-3205
The lattice site occupation of 3d-type impurities in Cr3Si doped with Fe, Co and Ni were studied using the Extended X-ray Absorption Fine Structure (EXAFS) technique, X-rays and magnetic susceptibility measurements. The EXAFS measurements were performed particularly carefully on the K-edge of chromium and cobalt. EXAFS data strengthened by simulations of the spectra show unambiguously that the impurities are occupying mostly Cr-sites. The magnetic state of the alloys has been studied theoretically using the Wien2k code. It is observed that if calculations are not carried out on an appropriately fine mesh of points in k-space, one can get the result indicating ferromagnetism although the overall magnetic moment per formula unit is weak. 相似文献
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We have investigated the local atomic structure of amorphous TM-Ti alloys (TM = Co, Ni, Cu) produced by Mechanical Alloying by means of EXAFS analyses on TM and Ti K-edges. Coordination numbers and interatomic distances for the three alloys where found and compared. EXAFS results obtained indicated a shortening in the unlike pairs TM-Ti as the difference between d electrons of TM and Ti atoms increases, suggesting an increase in the chemical short range order (CSRO) from TM = Co to Cu.Received: 12 October 2003, Published online: 9 April 2004PACS:
61.43.Dq Amorphous semiconductors, metals, and alloys - 61.10.Ht X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. - 81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation 相似文献
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Zhengquan Tan J. I. Budnick
B. L. Chamberland
G. Tourillon
《Physica C: Superconductivity and its Applications》1989,160(5-6):571-574Cu K-edge and La L3-edge X-ray absorption spectra have been measured on a series of nominal LaxxCuO4 samples with x≤2.00. The extended X-ray absorption fine structure (EXAFS) results show that the x<2.0 samples always consist of stoichiometric (La/Cu=2/1) La2CuO4 and CuO. The number of La vacancies in the La2CuO4 structure, if any, should be very small. The sensitivity of the EXAFS technique to impurity phases under favorable conditions is demonstrated. 相似文献
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S. Majumdar R.K. Singha K. Das M. Chakraborty A.K. Das S.K. Ray 《Physica B: Condensed Matter》2008,403(12):2059-2064
Ribbon samples of Cu0.95Co0.05 were prepared by melt spinning method to perform systematic investigations on structure and transport properties as a function of annealing temperature. X-ray diffraction study shows that the ribbon is polycrystalline with a strong 2 0 0 texture along the surface normal of the as-quenched Cu0.95Co0.05 ribbon and the degree of texture is enhanced upon annealing. The compressive stress, which relaxes upon annealing, is observed in as-quenched ribbon. The resistivity, which is higher in as-quenched ribbon, decreases toward the bulk value of Cu upon annealing. The compressive stress and higher resistivity in as-quenched ribbon are attributed to the incorporation of Co atoms/particles in Cu matrix. The decrement of the stress and resistivity upon annealing is due to the precipitation of Co atoms from the Cu matrix, segregating as Co or Co-rich Cu grains as observed from the transmission electron microscopy measurements. 相似文献
8.
本文就EXAFS研究非晶态合金原子近邻结构时曲线拟合数据分析中能量阈值调节参量对分析结果的影响进行了模型计算,并且提出了解决方法。 相似文献
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本文报道利用单辊方法制备的非晶Nd3Fe81B16合金的晶化及其对磁性和M?ssbauer谱的影响。发现在非晶Fe81B19合金中用3at%Nd取代B,使非晶Fe81B19合金的晶化温度提高88℃。在适当的退火条件下晶化后样品在室温下的磁性是:σs=189emu/g,σr/σs=0.7,iHc=2.15kOe,Br≈12kG,bHc=2kOe,(BH)max≈8MGOe。与目前广泛使用的六角铁氧体相比,bHc相近,但Br和(BH)max远比六角铁氧体高。这种材料仅含有少量的Nd,因此可能开发为一种新的廉价永磁材料。本文对少量Nd的添加对非晶FeB合金的晶化温度,磁性和M?ssbauer谱的影响进行了讨论。初步探讨了高矫顽力的来源,认为它的磁化和反磁化过程可以用畴壁钉扎理论解释。
关键词: 相似文献
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采用真空非自耗电弧炉熔炼, 然后进行固溶处理制备了Mn70Fe30-xCox (x=0,2,4) 试样. 运用X射线衍射分析、显微组织分析、差示扫描量热法 (DSC)、标准电阻应变计法等实验方法, 研究了添加Co 对Mn-Fe合金的磁诱发应变 (magnetic-field-induced strain, MFIS) 性能的影响. 研究表明, Mn70Fe30-xCox (x=0,2,4)试样在室温下为单一的γ相组织. 随着Co含量的增加, Mn70Fe30-xCox (x=0,2,4)试样的磁性转变温度TN (Neel点) 呈降低的趋势, 但都高于室温, 在室温下呈现反铁磁性; Mn70Fe30-xCox (x=0,2,4) 试样的最大磁诱发应变也呈增加的趋势. Mn70Fe26Co4试样的MFIS 在1.1 T时达到60 ppm.
关键词:
MnFe合金
Co
磁诱发应变 相似文献
12.
J. Antonowicz A. Pietnoczka T. Drobiazg G.A. Almyras D.G. Papageorgiou G.A. Evangelakis 《哲学杂志》2013,93(15):1865-1875
We have used the X-ray absorption fine structure method and molecular dynamics (MD) simulations to characterize atomic order in Cu-Zr metallic glasses (MGs). The microstructure of these MGs is described in terms of interconnected icosahedral-like clusters (superclusters) which are basic building units reproducing the stoichiometry of the system. The equilibrium MD configurations are used as an input for ab initio calculations of the extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra. The theoretical EXAFS and XANES spectra are compared with those measured for rapidly quenched glassy Cu-Zr alloys. We demonstrate that the experimental results are well reproduced by EXAFS modeling of the population of the superclusters derived from the MD configuration. The average local structural motif can be approximated by Cu-centered icosahedral-like cluster satisfying the condition of maximal local packing efficiency and approximating the system stoichiometry. The simulated XANES exhibits good agreement with experiment, indicating that the atomic order of the MD configuration is consistent with that of the real alloy structure over distances of about 1?nm. 相似文献
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遗传算法在EXAFS谱图解析中的应用 总被引:2,自引:0,他引:2
扩展X射线吸收精细结构(EXAFS)谱是研究物质原子近邻结构和表面结构的有力工具。EXAFS谱的解析通常采用标准样品比较法或最小二乘曲线拟合方法。但前者对标样的要求很高,而后者则参数初值难以确定,且结果有时不唯一。本文提出一种EXAFS曲线拟合的新方法一遗传算法,并对单配位层Cu样品的EXAFS谱图进行了解析,取得满意的结果。 相似文献
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The extended X-ray absorption fine structure (EXAFS) associated with the K absorption discontinuity of copper has been studied in the pure metal and in some copper-gallium and copper-germanium alloys, using a bent crystal X-ray spectrograph. The results obtained are discussed in the light of the recent theory of EXAFS proposed by Lytle, Sayers and Stern. It has been shown for the first time that there exists in alloys a correlation between the EXAFS parameter α1 and e/a ratio. This correlation has been used to obtain the value of the lattice parameter “a” for Cu-27 at.% Ge alloy, which is not available in literature. 相似文献
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Spin-resolved X-ray photoelectron spectroscopy (SRXPS) and high resolution X-ray photoelectron spectroscopy (HRXPS) studies of the valence bands of ferromagnetic Fe, Co, Co66Fe4Ni1B14Si15 and Ni are reported. The SRXPS and HRXPS spectra are compared with theoretical densities of states (DOS) that are corrected for photoelectric cross section variations within the valence band. Agreement between theory and experiment is very good for ferromagnetic Fe and Co66Fe4Ni1B14Si15. For Co metal, experiment agrees poorly with theory incorporating a 1.5 eV exchange splitting. Agreement is improved if a reduced Co exchange splitting of 1.2 eV is adopted theoretically. The reduced exchange splitting is attributed to valence electron correlation in Co metal. Ferromagnetic Ni shows poor agreement between experiment and theory. The SRXPS Ni spectra demonstrate that most of the disagreement concerns the ↑-spin channel. 相似文献
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《Journal of Electron Spectroscopy and Related Phenomena》2002,125(2):89-98
We have measured and analyzed Co K-edge X-ray absorption near edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) near edge spectra in crystalline and amorphous GdCo2 alloys. We have used a semi-relativistic full multiple scattering approach to the analyses of the XMCD spectra. A general formula is obtained which is applicable to randomly oriented systems in space. Useful information is obtained on both the electronic and geometric structure around a Co atom. The difference in XANES and XMCD spectra between crystalline and amorphous GdCo2 is well explained by models referring to the anomalous X-ray scattering result, where three Gd atoms in the second shell are removed away. The calculated XANES are not so sensitive to the electronic structure, whereas the calculated XMCD spectra are rather sensitive to the spin polarization on Co atoms. The result shows that the spin polarization on Co atoms in GdCo2 alloys is smaller than that in Co metals. 相似文献
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Dmitry A. Kukuruznyak Jerome G. Moyer Michael S. Prowse Nam Nguyen John. J. Rehr Fumio S. Ohuchi 《Journal of Electron Spectroscopy and Related Phenomena》2006,150(2-3):282-287
In very rare circumstances, X-ray photoemission spectra of copper in spinel oxides exhibit a “negative binding energy shift”. The origin of such an anomalous XPS chemical shift was investigated. A metastable Ni0.48Co0.24Cu0.6+xMn1.68−xO4 (0 < x < 0.6) spinel was fabricated at 600 °C using a low-temperature solution technique. The binding energy of the 2p3/2 level of copper (930.8 eV) is found 1.9 eV lower than that of Cu0 (932.7 eV). XPS and EXAFS studies revealed that the post-thermal annealing between 600 and 800 °C undergoes an irreversible cubic-to-tetragonal phase transformation through oxidation–reduction reaction Cu1+ + Mn4+ Cu2+ + Mn3+, and only tetrahedral Cu1+ species in the cubic spinel shows this anomalous chemical shift. The negative shift of the core levels was correlated to an equal shift of the Cu 3d valence band levels. XPS valence bands from the samples annealed at different temperatures were compared to DOS calculations. The DOS computations were performed with FEFF-8.1 code using experimental crystal parameters established by the EXAFS analysis. It was found that the tetrahedral Cu1+ in the 600 °C annealed sample exhibits localization of the 3d orbitals showing behavior characteristic to zinc. The completely filled and isolated 3d electron shell appears as a false valence band edge in the XPS spectrum. The position of the Cu 3d, and other core levels, is established by oxygen pinning the Cu valence band levels and by the fixed value of the p–d gap characteristic to the tetrahedral copper environment in this spinel. 相似文献
20.
H.L. Bai E.Y. Jiang C.D. Wang R.Y. Tian 《Applied Physics A: Materials Science & Processing》1998,66(4):423-433
286 , 176 (1996)]. (1) The interdiffusion critical wavelengths were calculated as 2.00–2.04 nm at temperatures ranging from 473
to 523 K, which is equal to those of Co/C multilayers within the experimental error, indicating that the interdiffusion behaviours
in the CoN/CN multilayers are still decided by the thermodynamic properties of the Co-C system. (2) The effective interdiffusivities
and macroscopic diffusion coefficients are smaller. (3) The activation energy for diffusion is larger. The features imply
that it is possible to improve the thermal stability of Co/C multilayers by doping with N atoms.
The high-temperature annealing results imply that the destructive threshold of the CoN/CN multilayers is 100–200 °C higher
than that of Co/C multilayers. The small-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period
expansion of the multilayers is only 4% at 400 °C, and the interface pattern still exists even if they were annealed at 700 °C.
The large-angle X-ray diffraction and transmission electron microscopy analysis reveal that the crystalline process is significantly
retarded if doped with N atoms, leading to a smaller grain size at higher annealing temperatures.
The significant improvement of the thermal stability can be interpreted with Raman spectroscopy and X-ray photoelectron spectroscopy
analysis. The Raman spectra give the evidence that the formation of the sp3 bonding in the CN sublayers can be suppressed effectively by doping with N atoms, and thus the period expansion resulting
from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra give information
about existence of the strong covalent bonding between N atoms and the ionic bonding between Co and N atoms, which can slow
down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc
Co and hcp Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420 °C,
leading to the suppression of the grain growth.
Received: 29 May 1997/Accepted: 8 September 1997 相似文献