Fe和Co对Ni2MnGa合金(110)马氏体孪晶界面电子结构的影响

利用密度泛函理论研究了Fe,Co两种合金元素对Ni2MnGa合金(110)马氏体孪晶界面电子结构的影响.分别从界面能、偏聚能、磁矩、键序和电子态密度等角度对合金元素在界面处的掺杂效应进行了分析和比较.计算结果表明,在对界面的钉扎作用上,Co的界面掺杂效应较Fe的掺杂效应强;对于界面磁性的影响,Fe掺杂对界面磁结构的作用比Co掺杂显著.     

La3Co29-xFexSi4B10的择优占位、电子结构和晶格振动性质的理论研究

分别用第一性原理及原子间相互作用势对初始模型进行几何优化, 所得稳定结构的晶格参数均与实验值符合较好. 通过第一性原理密度泛函理论, 计算了稳定结构La₃Co_29-xFe_xSi₄B₁₀化合物择优占位情况, 计算结果表明, Fe原子最择优替代Co 原子的2c晶位, 择优占位顺序为2c > 8j1 > 8i2 > 8j2 > 8i3 > 16k > 8i1, 这与实验结果非常符合. Fe原子每次只替代不同晶位的一个Co原子时, La₃Co_29-xFe_xSi₄B₁₀ 体系的晶格常数几乎不变, 磁矩却发生了有趣的变化. 当Fe原子沿着择优顺序依次替代不同晶位的所有Co原子时, 随着La₃Co_29-xFe_xSi₄B₁₀体系中Fe原子含量的增多, 其电子态密度整体向左移动. Fe原子完全替代Co时, 与未掺杂时相比体系的总磁矩增加. 最后, 利用原子间相互作用势进一步预测了La₃Co_29-xFe_xSi₄B₁₀体系的晶格振动及热力学性质. 在低频部分, 振动模式主要由质量较大的Co, Fe和La元素作贡献; 随着掺杂原子Fe的增多, 体系的截止频率先减小后增多, 中频部分由Si元素引起的振动模式减少; B-B强相互作用引起了高频部分的振动模式. 基于声子态密度预测了不同数量Fe掺杂后体系的比热、熵和德拜温度的变化, 当Fe 含量大于Co时, 德拜温度明显升高.     

Fe和Co元素在铁磁性形状记忆合金Mn50Ni25－xFe(Co)xGa25中的作用

为了进一步改善材料的性能和探索新的材料，将Mn₂NiGa合金中的Ni元素分别用Fe和Co替代，制备了Mn₅₀Ni_25-xFe(Co)_xGa₂₅系列合金. 研究了Fe和Co元素对Mn₂NiGa合金的结构、马氏体相变行为、磁性和机械性能等方面的影响. 关键词： 铁磁形状记忆合金 Heusler合金 50Ni_25-xFe(Co)_xGa₂₅')" href="#">Mn₅₀Ni_25-xFe(Co)_xGa₂₅     

过渡金属与氮共掺杂ZnO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框架下的第一性原理平面波超软赝势方法,结合广义梯度近似(GGA)研究了过渡族金属(Mn,Fe,Co,Cu)与N共掺杂ZnO的能带结构、电子态密度分布、差分电荷密度和光学性质.计算表明Mn，Fe，Co与N共掺ZnO的光学性质与Mn，Fe，Co单掺杂相近，但是过渡族金属与N共掺杂有利于获得p型ZnO. 关键词： ZnO 第一性原理 电子结构 光学性质     

第一性原理研究合金元素对逆变奥氏体在Cu沉淀上异质形核的影响

超高强度马氏体钢的力学性能强烈依赖于逆变奥氏体的形状、尺寸及含量.通常,提高逆变奥氏体含量,有助于改善超高强度钢的塑韧性.对含Cu马氏体淬火钢时效处理时, Cu粒子会在马氏体组织边界沉淀,并作为质点促进逆变奥氏体形核.为了探索不同合金元素对逆变奥氏体在Cu沉淀上异质形核的影响,本文利用第一性原理方法研究了合金元素X (X=Cr, Al, Mo, W, Ni, Co, Mn)对Cu/γ-Fe界面性质的影响,并分析了合金原子替换界面处Cu和Fe原子前后界面的黏附功、界面能和电子结构.研究结果表明,合金元素Cr,Mo, W, Mn替换Cu/γ-Fe界面处Cu原子时, Cu/γ-Fe界面处产生强烈的X—Fe共价键,黏附功增大且界面能减小,显著提高界面稳定性,促进γ-Fe在Cu沉淀上异质形核.而替换界面处Fe原子时,界面稳定性变化很小,掺杂原子与相邻的其他原子成键较弱.     

掺杂对Ni51.5Mn25Ga23.5相变行为和磁性的影响

通过往母合金Ni_51.5Mn₂₅Ga_23.5掺入7种IVA, VA和VIA 过渡族元素得到系列掺杂合金Ni_51.5Mn₂₃M₂Ga_{23 .5}.M为掺杂元素.实验结果表明，掺杂效应一般引起马氏体相变温度的下降，其中，W 的掺杂是7种元素中唯一使相变温度升高的特例，且出现了中间马氏体相变.同时，在价电子 浓度不变的情况下，相变更敏感于原子的尺度效应.实验发现，Ti，Zr，Hf，V四种非磁性元 素的掺杂使Mn原子磁矩减小，而Nb，Ta，W三种非磁性元素的掺杂却可以明显地增大Mn原子 的磁矩.在考察掺杂效应时，不能忽略马氏体相变引起的晶格变化对材料磁性的影响. 关键词： NiMnGa 掺杂 马氏体相变 磁性     

Co含量对Fe3Si合金磁学性能的影响

采用基于密度泛函理论（DFT）的赝势平面波法,对过渡金属Co掺杂Fe₃Si进行几何结构优化,计算Co含量对Fe₃Si合金磁学性质的影响.研究表明：Fe_3-xCo_xSi的磁性主要来源于过渡金属元素Fe和Co,并且相对于A、C位的Fe和Co原子,B位Fe的原子磁矩较大;在0≤x≤0.75范围内,随着Co含量的增大,Fe_3-xCo_xSi的总磁矩缓慢减小,在0.75≤x≤1.5时,其总磁矩迅速地增大;A、C位Fe原子的磁矩和合金总磁矩的变化趋势相同,Co原子的磁矩随着Co含量的增大缓慢地增大,原子的磁矩变化与自旋向上和向下方向的电荷转移有关.     

Mg,Al掺杂对LiCoO2体系电子结构影响的第一原理研究

为了研究Mg, Al掺杂对锂二次电池正极材料LiCoO₂体系的电子结构的影响，进而揭示Mg掺杂的LiCoO₂具有高电导率的机理，对Li(Co, Al)O₂和Li(Co, Mg)O₂进行了基于密度泛函理论的第一原理研究. 通过对能带及态密度的分析，发现在Mg掺杂后价带出现电子态空穴，提高了电导，并且通过歧化效应（disproportionation）改变了Co-3d电子在各能级的分布，而Al掺杂则没有这些作用. O关键词： 2')" href="#">LiCoO₂ 电子结构 第一原理 电导     

Co掺杂MgF2电子结构和光学特性的第一性原理研究

基于密度泛函理论（DFT）的第一性原理平面波超软赝势方法,计算了Co掺杂MgF₂晶体的几何结构、电子结构和光学性质.结果表明,Co掺杂导致MgF₂晶体结构畸变,可能发生一种类四方和斜方型结构相变.由于Co原子的加入,体系的禁带宽度减小,可观察到半导体—金属性转变.计算也表明,Co掺杂对静态介电常数和光吸收系数有重要调制作用,所得结果与最近实验测量很好相符,揭示了Co:MgF₂体系在光学元器件方面的潜在应用. 关键词： 密度泛函理论（DFT） 第一性原理 超软赝势 2')" href="#">Co掺杂MgF₂     

掺杂Fe对VH2解氢性能影响的第一性原理研究

采用密度泛函理论(DFT)的第一性原理的平面波超软赝势方法,研究了Fe掺杂对VH₂的电子结构和解氢性能的影响.通过计算Fe掺杂VH₂前后体系的合金形成热、V-H之间的重叠布居数、电子态密度、电子密度,发现Fe掺杂VH₂后,随着Fe含量增加,合金体系的晶胞参数和晶胞体积逐渐减少;体系的负合金形成热逐渐减少,且掺杂后体系的负合金形成热都比VH₂的负合金形成热小,体系的稳定性降低;电子态密度计算也显示Fe掺杂后费米能级处的电子浓度增加,体系稳定性降低;重叠布居数和电子密度计算表明掺杂后V-H之间的重叠布居数由0.1减小为0.08或0.09,V-H之间的电子密度减少,说明V和H原子之间的相互作用减弱,提高了VH₂的解氢性能.计算结果解释了实验现象. 关键词： Fe掺杂 电子结构 解氢性能 第一性原理计算     

A comparative study of magnetic relaxation in YBa2Cu3−x Fe x O7−y single crystals

The zero-field-cooled magnetization relaxation has been studied over wide temperature and field ranges on iron-doped YBa₂Cu₃O_7–y single crystals. The relationship between the twin boundary density, which depends on the iron composition, and the pinning strength of the flux lines is determined systematically. For magnetic fields up to 1 T the inductive critical current density decreases as the iron composition increases. The Bean critical state model and the Anderson-Kim thermally activated flux-creep model are utilized to analyze and interpret the experimental results.     

Electronic structure of a cobalt monolayer on Cu(100)

Angular resolved photoemission spectra using synchrotron radiation have been measured for different amounts of cobalt evaporated on Cu(100). At room temperature cobalt grows layer-bylayer forming well-ordered layers in registry with the substrate, as judged by AES, LEED and UPS measurements. The energy position and linewidth of the Cu peaks remain unchanged when cobalt is deposited onto the surface, suggesting a rather weak interaction between the d-bands of Co and Cu. The two-dimensional band structure of the monolayer of cobalt has been determined. We have obtained a value for the magnetic exchange splitting of ΔE_exch = 0.80 ± 0.15 eV, which is nearly identical to the bulk value. A shift in the energy positions of the critical points for the monolayer versus bulk of cobalt is interpreted in terms of a narrower 2D density of states in the monolayer as compared to the bulk. A resonant valence-band two-electron satellite has been found. The correlation energy and screening effects of the two d-holes are very similar to the corresponding bulk values, while the decreased intensity of the satellite at resonance compared to the one for Co(0001) suggests that there are more d-states relative to s-states in the monolayer than in a bulk cobalt single crystal, in agreement with recent models of the valence band electronic structure at surfaces.     

Spin fluctuations and Curie temperature in the compounds R2M17 with nonmagnetic elements

The magnetic properties of materials for permanent magnets based on binary compounds R₂M₁₇ (R=Y, Sm; M=Fe, Co), also including additions of the nonmagnetic elements N, Al, and Si, are investigated a the theory of dynamical fluctuations of the electronic spin density. It is shown that the Curie temperature is determined by the ratio of the exchange splitting energy (proportional to the magnetization at T=0) and the rms value of the fluctuations (proportional to the local spin susceptibility). The fluctuations are much larger in iron compounds than in cobalt alloys. This results not only in quantitative differences in their characteristics but also in a qualitatively different change in the properties of these materials on nitriding. Fiz. Tverd. Tela (St. Petersburg) 41, 77–83 (January 1999)     

Features of Electronic Structure of Intermetallic Compounds CeNi<Subscript>4</Subscript>M (M = Fe,Co, Ni,Cu)

The evolution of the electronic structure of CeNi₄M (M = Fe, Co, Ni, Cu) intermetallics depending on the type of nickel substitutional impurity is explored. We have calculated band structures of these compounds and considered options of substituting one atom in nickel 3d sublattice in both types of crystallographic positions: 2c and 3g. The analysis of total energy self-consistent calculations has shown that positions of 2c type are more energetically advantageous for single iron and cobalt impurities, whereas a position of 3g type is better for a copper impurity. The Cu substitutional impurity does not change either the nonmagnetic state of ions or the total density at the Fermi level states. Fe and Co impurities, on the contrary, due to their considerable magnetic moments, induce magnetization of 3d states of nickel and cause significant changes in the electronic state density at the Fermi level.     

Half-metallic magnetism of Co2CrX (X=As, Sb) Heusler compounds: An ab initio study

In this study, we present the electronic, magnetic, and structural properties of two novel half-metallic full-Heusler compounds, Co₂CrAs and Co₂CrSb, in cubic L2₁ geometry. The calculations are based on the density functional theory within plane-wave pseudopotential method and spin-polarized generalized gradient approximation of the exchange-correlation functional. The electronic band structures and density of states of the systems indicate half-metallic behavior with vanishing electronic density of states of minority spins at Fermi level, which yields perfect spin polarization. The calculated magnetic moments of both systems in L2₁ structure are 5.00 μ_B, which are largely localized on the chromium site. The energy gaps in minority spin states are restricted by the 3d-states of cobalt atoms on two different sublattices. The formation enthalpies for both structures are negative indicating stability of these systems against decomposition into stable solid compounds.     

Magnetism of mass-filtered nanoparticles on ferromagnetic supports

The magnetic properties of 3d-metal clusters significantly differ from bulk behavior and, for small clusters, strongly depend on the number of atoms within each cluster. Such phenomena are caused by a narrowing of electronic states and the high ratio of surface to volume atoms giving rise to enhanced magnetic orbital moments. However, even large Fe nanoparticles (6–12 nm) deposited onto ferromagnetic surfaces show enhanced orbital moments. At a low coverage large iron clusters on a cobalt film exhibit a nearly doubled value for the orbital moments when compared to bulk behaviour. With increasing coverage, the orbital moment is clearly reduced. Additionally, the spin and orbital moments of iron and cobalt in Fe₅₀Co₅₀ alloy clusters with a size of 7.5 nm on a nickel substrate have been investigated. FeCo alloys are known to exhibit very high magnetic moments for soft magnetic materials. PACS 73.22.-f; 75.75.+a; 81.07.-b     

The electronic structure of polymeric complex Co(thiazole)2Cl2 studied by first-principle calculation

One-dimensional dihalide-bridged polymer Co(thiazole)₂Cl₂ has been studied with the self-consistent full-potential linearized augmented plane wave method (FP_LAPW) based on the density functional theory (DFT). Spin distributions in ferromagnetic and antiferromagnetic states of it have been obtained by the calculation. The electronic structure and magnetic coupling between tow cobalt (II) ions along chain are discussed.     

Ground state of BaCoS2 as a set of energy-degenerate orbital-ordered configurations of Co2+ ions

The linear muffin-tin orbital method in the local density approximation (LDA + U) explicitly considering Coulomb correlations has been applied to calculate the electronic structure, magnetic moments, and parameters of the Heisenberg exchange interaction for cobalt ions in BaCoS₂. Five solutions close in total energy with various orbital ordering of Co²⁺ ions and almost identical spin magnetic moments μ = 2.32μ_B of the Co²⁺ ion 3d-shell have been found. The BaCoS₂ ground state can be considered as a set of energy-degenerate orbital-ordered configurations of Co²⁺ ions in the high-spin state.     

Calculation of the electronic structure and hyperfine fields for Fe1 − x Co x B and (Fe1 − x Co x )2B compounds by the Korringa-Kohn-Rostoker method

The magnetic properties of Fe_{1 ? x} Co _x B and (Fe_{1 ? x} Co _x )₂B disordered compounds were investigated using first-principles calculations of the electronic structure in the framework of the density functional theory with the Korringa-Kohn-Rostoker method. The concentration dependences of the magnetic moments and the electron density were calculated for the Fe_{1 ? x} Co _x B solid solutions. The results obtained were used to analyze in detail and to interpret the transition from a magnetic phase to a nonmagnetic phase, which was previously revealed from the experiments in the compounds under investigation. The performed analysis of the calculated hyperfine fields induced by the electronic shells at the iron and cobalt atoms in the (Fe_{1 ? x} Co _x )₂B borides made it possible to explain the experimentally observed magnetic anisotropy.     

First-principle study on the electronic structure and the anti-ferromagnetic properties of the organic-inorganic hybrid compound [Co(μ1,3-SCN)2(μ1,6-dmpzdo)]n

The electronic and the magnetic properties of the molecule-based magnet [Co(μ_1,3-SCN)₂(μ_1,6-dmpzdo)]n (where dmpzdo=2,5-dimethylpyrazine-1,4-dioxide) have been investigated using first-principles, namely density-functional theory (DFT) with the generalized gradient approximation (GGA) method and the full-potential linearized augmented plane-wave method (FP_LAPW). The total energy, the spin magnetic moments and the density of states (DOSs) were all calculated and spin distributions in ferromagnetic and anti-ferromagnetic (AFM) states of it have been obtained by the calculation. The electronic structure and magnetic coupling between cobalt ions along chain are discussed, and the calculations reveal that the compound [Co(μ_1,3-SCN)₂(μ_1,6-dmpzdo)]n has a stable anti-ferromagnetic ground state, which is in good agreement with the experimental results.