Defect-mediated nucleation of α-iron in Au-Fe alloys
摘要:
The low-temperature magnetic properties of Au-Fe alloys, such as spin-glass or mictomagnetic behavior, are known to be dependent on thermal history and therefore on the atomic order in the sample. The nature of this order is still controversial, and the discussion includes the presence of short-range order as well as the precipitation of Guinier-Preston (GP) zones. It is frequently neglected in this context that there is a miscibility gap in Au-Fe at low temperatures, where ferromagnetic alpha-iron should coexist with the solid solution. The conditions for alpha-iron nucleation have not been studied systematically in the range of compositions, where spin-glass or mictomagnetic behavior appears. We have used a combination of Mossbauer spectroscopy, x-ray diffraction, and small-angle scattering to investigate the nucleation of alpha-iron in Au0.85Fe0.15 and Au0.75Fe0.25: (1) This nucleation appeared to be a discontinuous process related to the presence of a high dislocation density. (2) No homogeneous precipitation, like the formation of GP zones, was observed. (3) All experimental results seem to be in agreement with the hypothesis of a (1-1/2(0)) special-point short-range ordering in the solid solution.
Ultrahigh Mass Activity for Carbon Dioxide Reduction Enabled by Gold–Iron Core–Shell Nanoparticles
摘要:
Wide application of carbon dioxide (CO2) electrochemical energy storage requires catalysts with high mass activity. Alloy catalysts can achieve superior performance to single metals while reducing the cost by finely tuning the composition and morphology.. We used in silico quantum mechanics rapid screening to identify Au-Fe as a candidate improving CO2 reduction and then synthesized and tested it experimentally. The synthesized Au-Fe alloy catalyst evolves quickly into a stable Au-Fe core-shell nanoparticle (AuFe-CSNP) after leaching out surface Fe. This AuFe-CSNP exhibits exclusive CO selectivity, long-term stability, nearly a 100-fold increase in mass activity toward CO2 reduction compared with Au NP, and 0.2 V lower in overpotential. Calculations show that surface defects due to Fe leaching contribute significantly to decrease the overpotential.
Critical behavior near the para–ferromagnetic transition of the reentrant systems Au0.81Fe0.19 and Ni0.78Mn0.22
作者:C Haetinger、P Pureur、L Ghivelder
DOI:10.1016/s0304-8853(00)00681-8
日期:2001.5
Abstract The static critical exponents α, β, γ and δ near the Curie temperature of the reentrantsystems Au0.81Fe0.19 and Ni0.78Mn0.22 are determined by a variety of methods. The values found for these indices are intermediate between the predictions for the 3D Heisenberg model and those characterizing a spin-glass transition.
摘要 重入系统Au0.81Fe0.19和Ni0.78Mn0.22在居里温度附近的静态临界指数α、β、γ和δ可用多种方法确定。为这些指数找到的值介于 3D 海森堡模型的预测和表征自旋玻璃转变的那些预测之间。
Magnetic properties of new glassy Fe–Au(Cu)–B alloys
作者:Nicoleta Lupu、Akihisa Inoue
DOI:10.1016/j.jmmm.2004.11.497
日期:2005.4
The evolution of the microstructure and soft magnetic properties of Fe76Au4-xCuxB20 and Fe87Au2-xCuxB11 melt spun ribbons prepared at different cooling rates were investigated. The samples are stable above room temperature and display saturation induction up to 1.79 T and magnetic permeabilities of over 2 x 10(4) at 300 K. The structure is not fully amorphous, as proved by DSC and HRTEM investigations, but consists of very small grains of about 10 nm, randomly dispersed in the amorphous residual matrix. The grains composition strongly depends on the B content. (c) 2004 Elsevier B.V. All rights reserved.
Stable Distribution Analysis of Internal Field Distribution in Au(Fe) Spin Glass System. I. Variation of the Distribution with Concentration
作者:Yukito Furukawa、Yutaka Nakai、Nobuhiko Kunitomi
DOI:10.1143/jpsj.62.306
日期:1993.1.15
Internal field distributions in Au(Fe) spin glass systems were evaluated from hyperfine field distributions obtained by Mossbauer spectroscopy. The internal field distributions of the specimens with 5 to 16.8 at.% Fe, are well expressed by stable distributions; limit distributions for the sum of large number of independent variables, defined in the probability theory. The function form of the stable distribution is specified by a characteristic index. Variation of the characteristic index as a function of the Fe concentration was explained by the fact that magnetic atoms are not randomly distributed in a continuum but are located in the lattice points only, as discussed by Klein.