Cluster ferromagnetism in InSb codoped with Mn and Zn

Using direct melting and quenching of InSb + 0.058-0.23 wt % Mn + 1.1 wt % Zn, we have prepared polycrystalline InSb〈Mn, Zn〉 solid solutions containing much less impurity phases in comparison with earlier studied InSb〈Mn〉 substitutional solid solutions containing manganese on the indium site. As shown by electron probe x-ray microanalysis and electrical and magnetic measurements, the synthesized solid solutions consist of InSb〈Mn〉 substitutional solutions and InSb〈Zn〉 interstitial solutions. The room-temperature hole concentration and magnetization of InSb〈Mn, Zn〉 p exceed those of InSb〈Mn〉. The electrical and magnetic properties of the magnetic material InSb〈Mn, Zn〉 fit well with indirect kinematic ferromagnetic exchange theory.     

InSb codoped with Mn and Zn: A new ferromagnetic semiconductor

We have studied the magnetic properties of In_{1 − x} Mn _x Sb substitutional solid solutions. The results indicate that, at Mn contents below 0.5 at %, the materials contain microinclusions close in composition to the ferrimagnetic compound Mn₂Sb, which has a layered structure with magnetically active manganese in two structurally inequivalent sites, Mn1 and Mn2. Zinc doping of Mn₂Sb breaks up one of its magnetic sub-lattices and converts the ferrimagnet to a ferromagnet. This property is basic to the proposed ferromagnetic semiconductor based on InSb codoped with Mn and Zn, which has a Curie temperature near 320 K.     

The electronic band structure of InN,InAs and InSb compounds

The electronic band structure of InN, InAs and InSb has been investigated by ETB. The ETB method has been formulated for sp³d² basis and nearest neighbor interactions of the compounds and its energy parameters have been derived from the results of the present first principles calculations carried on InN, InAs and InSb. It has been found that the present ETB parameters can produce the band structure of the compounds successfully.     

S、Mn共掺杂锐钛矿相TiO2电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法研究了纯锐钛矿相TiO2,S、Mn分别单掺杂及共掺杂TiO2的晶体结构、杂质形成能、电子结构、光学性质和带边位置。计算结果表明,掺杂后TiO2的晶格发生畸变,原子间的键长、原子的电荷量以及晶体体积都发生变化,导致晶体中八面体偶极矩增大,从而有利于光生电子-空穴对的分离;S掺杂在TiO2的价带顶部形成杂质能级,Mn掺杂在TiO2的导带下方和费米能级附近形成杂质能级,共掺杂后TiO2禁带宽度变窄,光学吸收带边发生红移,TiO2在可见光区有明显的吸收;同时S、Mn共掺杂后TiO2的带边位置发生了明显变化,氧化还原能力增强,有利于提高光催化效率     

Effect of boron and sulphur on the electronic structure of grain boundaries in Ni

The first-principles discrete variational method is employed to study the effect of boron and sulphur on the electronic structure of the Ni grain boundary (GB). The calculated results show that boron does not strongly influence (only slightly decreases) the bonding between the atoms of the metal. In addition, B forms the strong bonding state with its neighbouring metal atoms. Our study also indicates that S strongly decreases the bonding between the atoms of the metal, and that the bonding tendency between S and the atoms of the metal across the GB plane is very weak. The calculations of environment-sensitive embedding energies show B has the strong site-competition ability and can successfully drive out S from the GB region. We conclude that the influence of impurities segregating on the GBs is closely associated with their effects on: (i) the decrease of the bonding between the atoms of the metal due to the presence of impurities; (ii) the bonding between the impurity atom and the atoms of the metal; and (iii) the site-competition ability of impurity atoms.     

Element-specific electronic structure of Mn dopants and ferromagnetism of (Zn,Mn)O thin films

Element-specific electronic structure of (Zn,Mn)O thin films with various Mn concentrations has been investigated using X-ray absorption and emission spectroscopy. According to comparison between the experimental spectra and the density functional theory calculations (partial density of states and exchange interactions for various Mn defect configurations), the substitutional Mn impurities do not induce ferromagnetism in (Zn,Mn)O samples. The ferromagnetic properties can be obtained when defect configurations consisting of both substitutional and interstitial Mn atoms are present. The ferromagnetism in ZnO-based magnetic semiconductors is favored to be Ruderman-Kittel-Kasuya-Yoshida type and the established theoretical model is in a good agreement with the X-ray spectroscopic measurements.     

反铁磁性交换作用对p、n型掺杂的GaAs居里温度的影响

居里温度与载流子浓度反铁磁性交换作用有着密切联系,定量分析反铁磁性交换作用对p型及n型GaAs材料的居里温度的影响,计算证明,反铁磁性交换作用对p型和n型掺杂的GaAs居里温度的影响有着本质的区别。p型半导体材料的居里温度仅仅与反铁磁性交换作用有关,而与掺杂浓度无关;对n型半导体居里温度与反铁磁性交换作用和掺杂浓度都有关,而且高掺杂浓度下居里温度比低掺杂浓度下居里温度低。     

GMR in Ni/Cu multilayers: an electronic structure study

Ab initio self-consistent semi-relativistic spin-polarized TB-LMTO energy band calculations have been carried out on Ni/Cu(100) multilayers, to study the in-plane as well as perpendicular to plane giant magnetoresistance (GMR) effects. The magnetic interaction energies, evaluated as a function of layer thickness, indicate that the antiferromagnetic ordering is a possible ground state for manifestation of GMR. Using the density of states at Fermi level and the Fermi velocity, GMR has been estimated as a function of the Cu spacer thickness.     

Fe0．875Mn0．125Si2的几何结构与电子结构的第一性原理研究

采用基于密度泛函理论的赝势平面波方法，对掺Mn的β-Fesi2的几何结构和电子结构进行了计算。计算表明：（1）杂质的掺入改变了晶胞体积及原子位置，掺杂是调制材料电子结构的有效方式；（2）在β-FeSi2中掺入杂质时掺杂原子的置换位置具有择位性，Mn掺杂时倾向于置换FeI位的Fe原子；（3）能带结构计算表明：掺Mn使得β-FeSi2的费米面向价带移动，形成了P型半导体。     

Effect of alloying on the electronic structure and magnetic properties of Fe,Co and Ni with Au and Ag

We use the self-consistent, augmented space recursion technique to study the electronic structure and magnetic properties of alloys of the transition metals, Fe, Co and Ni with the noble metals, Ag and Au. We analyse the effect of local environment and the hybridization between the constituent bands on the electronic and magnetic properties.     

ZG 1Mn19Ni3Al 铸焊结构低温性能研究

通过化学成分设计和金相组织设计，开发了一种适用于与１６Ｍｎ钢组成铸焊结构的新铸钢ＺＧ１Ｍｎ１９Ｎｉ３Ａｌ。研究了这两种材料组成的焊板在常温、低温（－１９６℃）下的力学性能和冲击断口形貌。试验结果表明，夹杂物和焊接线能量对其低温冲击韧性有着显著的影响。具有γ＋ε双相组织的ＺＧ１Ｍｎ１９Ｎｉ３Ａｌ钢用于低温（－１９６℃）铸焊结构中时要注意钢水精炼和采用适当的焊接线能量     

Photoreflectance of GaAs structures with a Mn δ-doped layer

The strength of the built-in electric field in gallium-arsenide structures with a δ-doped layer has been determined by photomodulation optical spectroscopy (photoreflectance) for different manganese contents in these structures. The samples under study have been grown by combining metal-organic chemical vapor deposition and laser sputtering of Mn and GaAs targets at a low temperature (T _g = 400°C). An increase in the Mn content in the δ-doped layer from zero to 0.35 monolayer leads to an increase in the built-in electric field (averaged over the surface region) from 14 to 25 kV/cm. The data obtained are in good agreement with the results of self-consistent solution of the Schrödinger and Poisson equations for the real (manganese) distribution profile.     

La2Ni7和LaMgNi7储氢合金电子结构的研究

采用密度泛函理论研究了La2Ni7和LaMg-Ni7储氢合金的电子结构,探讨了微观结构和合金宏观性能之间的关联性.结果表明,含Mg元素的LaMgNi7体系形成成键作用的Ni-Mg键,体系稳定性高于纯La2Ni7体系.同时LaMgNi7体系中的Ni-Ni键强度弱于La2Ni7体系中的相应键,降低了H进入体系的能量壁垒,改...     

Unit cell structure of crystal polytypes in InAs and InSb nanowires

The atomic distances in hexagonal polytypes of III-V compound semiconductors differ from the values expected from simply a change of the stacking sequence of (111) lattice planes. While these changes were difficult to quantify so far, we accurately determine the lattice parameters of zinc blende, wurtzite, and 4H polytypes for InAs and InSb nanowires, using X-ray diffraction and transmission electron microscopy. The results are compared to density functional theory calculations. Experiment and theory show that the occurrence of hexagonal bilayers tends to stretch the distances of atomic layers parallel to the c axis and to reduce the in-plane distances compared to those in zinc blende. The change of the lattice parameters scales linearly with the hexagonality of the polytype, defined as the fraction of bilayers with hexagonal character within one unit cell.     

Optical and electronic properties of some semiconductors from energy gaps

II-VI and III-V tetrahedral semiconductors have significant potential for novel optoelectronic applications. In the present work, some of the optical and electronic properties of these groups of semiconductors have been studied using a recently proposed empirical relationship for refractive index from energy gap. The calculated values of these properties are also compared with those calculated from some well known relationships. From an analysis of the calculated electronic polarisability of these tetrahedral binary semiconductors from different formulations, we have proposed an empirical relation for its calculation. The predicted values of electronic polarisability of these semiconductors agree fairly well with the known values over a wide range of energy gap. The proposed empirical relation has also been used to calculate the electronic polarisability of some ternary compounds.     

Raman scattering by electronic excitations in semiconductors and in highT c superconductors

Raman scattering by electronic excitations in normal and superconducting metals with complex Fermi surfaces is discussed. The theoretical results are applied to the case of high T_c superconductors. The possible implications of measurements of this scattering concerning the symmetry of the gap function is dealt with.     

Structural and electronic properties of NiMnSb Heusler compound and its interface with GaAs

We present first-principles calculations of NiMnSb/GaAs(001) junction within the framework of density functional theory (DFT) by using the plane wave pseudopotential method. After optimization of the atomic positions, we have investigated the main electronic and magnetic properties. We extract the band alignments for the majority and the minority spin channels. We found that the half-metallicity, which characterizes the NiMnSb in its bulk and epitaxial phase, is lost at the junction.     

Calculation of bulk modulus of titanium alloys by first principles electronic structure theory

A theoretical study of the electronic structure and binding energy of some hypothetical Ti-X alloys was carried out using a first-principles discrete variational cluster method. The formation energy of an alloying atom in solution of titanium was estimated based on such calculations, and the case of multi-constituent practical Ti alloys was considered in the dilute limit by a linear superimposition approach. The influences of alloying additions on the bulk modulus of the alloys were evaluated from the variation of the formation energy. The calculated moduli of the Ti alloys were found to vary linearly with the experimental values. This indicates that the present approach is appropriate for the simulation of modulus of titanium alloys. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calculation of heat exchange in pipes with spiral sheet intensifiers

A method of calculating the heat exchange in pipes with spiral sheet intensifiers is developed on the basis of a superposition of the effects of the separation and swirled motions of streams.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 6, pp. 965–969, December, 1979.