Application of a solvation shell analysis to the diffusivity of an interstitial species in binary substitutional solutions

A model is presented for the effect of substitutional solute elements on the diffusion coefficient of an interstitial species for low concentrations of both solutes. The model is based on the theory of absolute reaction rates and a Wagner random, noninteractive model for the substitutional solution, with Maxwell-Boltzmann statistics for the distribution of the interstitial atoms. Simplifying assumptions are made concerning the configuration of activated complexes, treating them as formed by the interstitial atom and the two nearest lattice atoms. The calculations are compared with experimental data reviewed for the diffusivity of carbon in Fe-Cr, Fe-Mn, Fe-Co and Fe-Ni alloys.     

Magnetoresistivity of single-crystal films of iron,cobalt, and nickel binary alloys

Magnetoresistivity measurements of binary systems of alloy films Fe-Co, Fe-Ni, and Co-Ni in the [100] direction for the alloy systems Fe-Co and Fe-Ni up to 25 wt. % Co and Ni, respectively, and in the [100] direction for the remaining alloys are presented. A test of Berger's theory on the influence of spin-orbit interaction on transition processes in ferromagnetic alloys of nickel is carried out. The results obtained are compared with the results derived from bulk polycrystalline samples [1, 2].     

Ordering and magnetism in Fe-Co: dense sequence of ground-state structures

We discover that Fe-Co alloys develop a series of ordered ground-state structures in addition to the known CsCl-type structure. This new set of structures is found from a combinatorial ground-state search of 1.5 x 10(10) bcc-based structures. The energies of the searched bcc structures are constructed with the cluster expansion method from few first-principles calculations of ordered Fe-Co structures. The set of new ground-state structures is explained from the decay behavior of the cluster expansion coefficients which allows us to identify a simple geometric motif common to all structures. The appearance of these FeCo superstructures offers a broader view of the ordering reactions in bipartite-lattice based binary alloys.     

Magnetic circular dichroism in soft X-ray resonant inelastic scattering

We discuss the application of resonant inelastic X-ray scattering to the study of magnetic systems in the soft X-ray range. To this end we distinguish two broad areas. In the first the layout of the experiment is such that the absorption magnetic circular dichroism (MCD) is not zero. In the second the magnetisation is perpendicular to the incident helical beam so that the absorption MCD is zero. In the first area we summarise published results on Fe-Co alloys and we present new data on Mn impurities in Ni together with calculations. In the second area we summarise published results on Ni in Ni-ferrite with final 3s shell excitation and we present new results on Co-metal and Co in Co-ferrite measured with a new approach. This is based on the incident energy dependence of the integral of the Raman spectrum in inner shell excitation (integrated resonant Raman scattering). The potentialities and the limitations of the above methods are critically presented. Received: 23 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

Investigation of the degree of occupancy of 3d and 4s bands of 3d metals and their alloys on the basis of a four-band model

A four-band model is used as the basis for obtaining relationships suitable for the calculation of a number of the s electrons in 3d metals and their alloys. The results are given of calculations of this number in Fe, Co, Ni, and Cu, and their Fe-Co, Co-Ni, and Ni-Cu alloys. A quantitative agreement is found between the number of the s electrons and the available published data. The results indicate the presence of vacant states in the d band of Cu and in the d subband of Ni, which is usually assumed to be completely filled. The results demonstrate shortcomings of the four-band model in explaining the magnitude of the normal Hall coefficient of Co and of Fe-Co, Co-Ni, and Ni-Cu alloys.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 71–77, May, 1980.     

Ground-state magnetovolume effects in alloys

We present a general theory for the magnetic contribution to the lattice parameters of ferromagnetic alloys of type A_χB_1?χ. This contribution is obtained as a function of χ. Calculations are given for the Fe-Co alloys and are in reasonable agreement with experiment. General trends in transition metal alloys are also found to be in agreement with the theory. The connection of the magnetovolume effect with the local moments on the various atoms is stressed. The effect is seen to be a sensitive probe of local magnetic order.     

Electronic density of states in pseudobinary compounds Y(Fe-Co)2 and Y(Mn-Co)2

Densities of states in pseudobinary compounds are calculated by making use of the coherent potential approximation (CPA) [3] and the recursion method. Applications are made for Y(Fe-Co)₂, Y(Mn-Co)₂ and Zr(Fe-Co)₂. The total and local magnetic moments of Y(Fe-Co)₂ and Zr(Fe-Co)₂ are calculated and compared with the experimental results.     

Hyperfine magnetic fields in Fe−Co alloys and their tempera ture dependences

We obtained⁵⁷Fe hyperfine field parameters from Fe₁−x-Co _x alloys (0≤x≤0.6) from 77 K to 900 K. We first discuss the origin of the low temperature hyperfine fields in terms of the 3d and 4s electrons at⁵⁷Fe atoms. The⁵⁷Fe hyperfine magnetic field (hmf) of Fe-Co alloys depends more weakly on temperature than the hmf of pure Fe. This temperature dependence occurs because the alignment of the magnetic moments at both the Fe atoms and at the Co atoms depend on temperature in the same way as the bulk magnetization of Fe-Co alloys.     

Field annealing effect on amorphous (FexCo1-x)85Nb15 alloys

The magnetic anisotropy induced by magnetic field annealing was examined for amorphous (Fe_xCo_1-x)₈₅Nb₁₅ alloys produced by a sputtering technique. An appreciably large uniaxial anisotropy was observed even at x = 0. The anisotropy constant (K_u) obtained was 2.3x10³ erg/cm³ at x=0, and it increased with x, showing a maximum of about 5.4x10³ erg/cm³ near x = 0.2. This compositional change in K_u was explained in terms of the directional ordering of magnetic Fe-Co atom pairs under the negative nonmagnetic interaction energy leading to a precipitation.     

The dynamical motion of atoms at the Ni(111) surface

One atom phonon spectral densities are presented for the vibrations of atoms at the Ni(111) surface both parallel and perpendicular to the surface. They are also presented for perpendicular motion of an adsorbed oxygen atom and the nickel atom immediately below it. The results are obtained using a continued fraction technique. They are compared with recent EELS data obtained by Ibach and Bruchmann.     

杂质浓度对Zr替位掺杂γ-TiAl合金的结构延性和电子性质的影响

以Zr替代Ti(或Al)掺杂γ-TiAl体系为研究对象, 掺杂浓度(摩尔比)分别为1/54, 1/36, 1/24和1/16. 采用基于密度泛函理论的第一性原理方法, 计算研究了Zr掺杂γ-TiAl体系的晶体结构及其稳定性、延性和电子性质等. 结果显示, Zr替位掺杂, 可以改变γ-TiAl基合金的结构对称性. 计算的形成能表明, Zr替代Ti原子会使体系的形成能降低, 而Zr替代Al原子会使体系的形成能增加. 因而, 在掺入γ-TiAl时, Zr更倾向于替代Ti 原子, 但是Zr替代Al原子也具有一定的可能性, 从而会产生多样的掺杂体系, 对于改善合金的性质具有重要意义. 对各个体系轴比的计算与分析表明, 当掺杂浓度为1.85 at%–6.25 at% 时, Zr替代Al原子会使体系的轴比减小、接近于1, 从而改善合金的延性效果明显. 能带结构显示各个Zr掺杂γ-TiAl体系均具有金属导电性. 对电子态密度和布居数的分析表明, Zr替代Al原子后, Zr与其邻近Ti原子的共价键结合强度大为降低, 导致合金体系中的Ti-Al(Zr)键的平均强度明显减弱, 金属键增强, 这是改善γ-TiAl合金延性的重要因素.     

A model for oxidation-driven surface segregation and transport on Pt-alloys studied by atom probe tomography

Using a purpose-built 3D atom probe, we have previously shown that exposure to oxidising gases (NO, N₂O, O₂) induces Rh surface segregation in Pt–Rh alloys, the extent of which is strongly dependent on treatment temperature, crystallographic plane and the presence of ternary alloy additions. In this paper, the segregation trends identified on three different crystallographic surfaces of Pt–Rh are analysed using thermodynamic and kinetic arguments. The segregation model we present is generic for diffusion on alloy surfaces in the presence of active gases. From it we obtain activation energies and diffusion coefficients for the processes of metal-oxide species diffusion both perpendicular to and laterally across the surface. Using these we propose a simple model for the interaction of chemically active gases with the surfaces of such alloys. Applying this understanding to sequential oxidation/reduction treatments would in principle allow improved control of the surface composition of alloy catalysts. Related applications of this model include optimisation of core–shell catalyst nanoparticles.     

Effect of a magnetic field on the atomic ordering of Fe-Co alloys in nanocrystalline films

The influence of a magnetic field on the process of atomic ordering in films Fe_0.5C_0.5 is studied. It is found that the process of atomic ordering of Fe-Co alloys in nanocrystalline films can be slowed down via the application of magnetic field of relatively low tension (hundreds of Oersted). The effect is due to the influence of magnetic field on diffusion of atoms.     

Specific features of the properties of Hg-Te lattice vibrations in Cd1 − y Hg y Te alloys enriched with CdTe

In alloys (solid solutions) Cd_{1 ? y} Hg _y Te enriched with CdTe, the properties of Hg-Te lattice vibrations are determined by a single-well lattice potential for the Hg atom located at the center of the anion tetrahedron. The HgTe-enriched alloys retain the anomalous properties of Hg-Te lattice vibrations, which are determined by a double-well lattice potential for the Hg atom located in the off-center position at low temperatures; a shallower well of the potential for the Hg atom located at the center of the anion tetrahedron is filled upon thermal activation. The polarizability of the ion pair in the TO mode of Hg-Te lattice vibrations with the Hg atom located at the center of the anion tetrahedron for the CdTe-enriched alloys considerably exceeds the polarizability of the pair with the off-center Hg atom for the HgTe-enriched alloys.     

Pt974Mn26/Co多层膜的磁性与磁光性质研究

用磁控溅射法制备了Mn含量一定、不同PtMn层厚度的Pt974Mn26/Co磁性多层膜系列，通过x射线衍射对该多层膜系列进行结构分析；测定了不同PtMn层厚度系列样品的磁滞回线、有效垂直各向异性，分析了饱和磁化强度和有效垂直各向异性变化的原因；通过测定该多层膜体系的克尔谱，分析了一定波长下克尔角随PtMn层厚度变化的规律.认为克尔角的变化是由于界面的合金化以及原子的极化减小所致. 关键词： 多层膜 磁性 磁光     

Heusler合金Mn2NiGe磁性形状记忆效应的第一性原理预测

运用基于密度泛函理论的第一性原理,对Hg₂CuTi型Mn₂NiGe的四方变形、晶体结构、磁性、电子结构、压力响应等进行了计算.计算结果表明: 1)在由立方结构至四方结构的转变中,在c/a约为1.34处存在一个稳定的马氏体相;2)在奥氏体态和马氏体态下,Mn原子均是Mn₂NiGe总磁矩的主要贡献者,但Mn(A),Mn(B)原子磁矩的值不等且呈反平行耦合,因而Mn₂N 关键词： 第一性原理 磁性形状记忆 四方变形 马氏体相变     

Ultrafine Fe-Co nanowires: Fabrication and heat treatment influence on the structure and magnetic properties

Ultrafine nanowires of Fe-Co with a diameter around 15 nm have been fabricated by electrodeposition method using anodic porous alumina as a template. The alloy nanowires were in the form of arrays and consisting of polycrystalline structures. They showed obvious shape anisotropy parallel to the axis of nanowires and the perpendicular coercivity (Hc_⊥) was found to be 2576.8 Oe which is higher than any coercivity value reported in the literature. The effects of critical factors such as heat treatment and temperature of annealing on the structure and magnetic properties of the ultrafine nanowire arrays were studied and discussed.     

Mg-Al系工业合金牌号的成分式解析

Mg-Al系牌号是应用最广的镁基工业合金,但其牌号背后的成分根源一直未知,构成研发新合金的主要障碍.本文应用描述固溶体短程序结构特征的团簇共振模型,得到了Mg-Al二元固溶体的最理想化学结构单元[Al-Mg_(12)]Mg_1,然后对《the American Society for Testing Materials》手册中所有Mg-Al系工业合金牌号进行成分解析,得到相应团簇成分式,如AZ63A合金解析后的团簇成分式为[Al_(0.78)Zn_(0.16)-Mg_(12)]Mg_(1.04)Mn_(0.02),AZ81A合金解析后的团簇成分式为[Al_(0.97)Zn_(0.03)-Mg_(12)]Mg_(0.98)Mn_(0.02).再根据成分式与化学结构单元之间的误差,对比该牌号合金的力学性能,验证了该化学结构单元在Mg-Al体系中的准确性,揭示出看似复杂的工业合金牌号后面隐藏的简单成分规律,为发展Mg-Al体系合金指出了一个全新的途径.     

The atomic radius of a solute in alloys of the noble metals

In the f.c.c., disordered, binary alloys of the noble metals, the deviations from Vegard's Law which occur, are studied with emphasis on the shielding of the charge of a polyvalent solute by the conduction electrons of the solvent. This shielding is studied with an empty core Fermi-Thomas Pseudopotential which is used to calculate the value of the effective valence of a number of solutes in alloys of copper and silver. When Vegard's Law is applied to these alloys, the value of the effective valence is assigned to the charge on a solute atom instead of the conventional valence. We take the value of the cancellation radius for a given atom equal to the expectation value of the radius of an electron in the outermost closed S shell of the atom. The radius of a given solute atom in copper and silver is calculated with our Pseudopotential. These theoretical results are compared with the value of the “apparent atomic diameter” of a solute in these solvents, a concept originally proposed by Axon and Hume-Rothery. Some comments are also made on alloys of gold.