组份对铁基非晶合金晶化温度的影响

本文系统研究了(Fe_1-xM_x)₈₄B₁₆系非晶合金(x=0.02—0.20;M=Ti,Zr,V,Nb,Ta,Cr,Mo,W,Mn,Co,Ni)的晶化温度与组成的关系。晶化温度随M=VIIB,VIB,VB,IVB元素的顺序和x值的增大而提高。M=VIII族(CO,Ni)元素时,晶化温度基本相同,并随x值的增大略有降低。对于被研究的95个Fe基非晶合金,晶化温度在700—825K的约占85％,熔点Tm/晶化温度T_cr约为1/2,在0.42—0.62之间,符合Sakka规则。Fe_1-x-yB_xSi_y的T_cr>Fe_1-xB_x>Fe_1-x-yB_xP_y。对上述规律性,从组份、扩散、相图以及晶化温度与合金元素外层平均电子浓度/α的关系进行了讨论。 关键词：     

3d过渡金属原子单层在Pd(001)表面磁性的第一性原理研究

用第一性原理基础上的超软赝势方法的总能计算，研究了3d过渡金属(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)在Pd(001)表面的单层p(1×1)和c(2×2)结构的表面磁性和总能. 所得结果表明：对于Sc, Ti, V和Cr只存在p(1×1)的铁磁性结构，而Mn只有c(2×2)的反铁磁结构存在. Fe, Co和Ni这三种元素上述两种结构都存在，但是总能上p(1×1)的铁磁结构要低些，因此是比较稳定的结构. 而Cu和Zn在该表面上的单层中不存在上述两种结构. 对于V的p(1×1)铁磁结构，计算得到的每个V原子磁矩为2.41μ_B，大于用全电子方法得到的0.51μ_B. 两种计算方法得到其他金属原子 (Cr，Mn，Fe，Co，Ni)的表面磁矩比较相近，都比孤立原子磁矩略小. 关键词： Pd(001)表面 过渡金属原子单层 表面磁性     

非晶态(Fe1-xVx)84B16合金的磁性和电性

用单辊急冷法制备了非晶态(Fe_1-xV_x)₈₄B₁₆(x=0,0.02,0.04,0.06,0.10)合金的薄带,分别用磁天平和四端引线法测量了饱和磁化强度和高温电阻率的温度关系。得到平均每个磁性原子的磁矩随V含量的增加近似线性下降,计算出每个Fe原子和每个V原子的平均磁矩分别为2.08μ_B和-5.08μ_B。居里温度T_c从x=0时的622K下降到x=0.10时的478K。利用自旋波激发公式:σ(T)=σ(0)(1-BT^* 关键词：     

掺杂对Ni51.5 Mn25 Ga23.5相变行为和磁性的影响

通过往母合金Ni51.5Mn25Ga23.5掺入7种ⅣA,ⅤA和ⅥA过渡族元素得到系列掺杂合金Ni51.5Mn23M2Ga23.5.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.     

原子替位掺杂对单层Janus WSeTe电子结构的影响

基于第一性原理计算系统地研究了氮族、卤族和3d过渡金属元素(Ti, V, Cr, Mn, Fe, Co)替位掺杂对单层Janus过渡金属硫族化合物WSeTe电子结构的影响.通过对能带结构、电荷转移以及磁性的分析,发现氮(卤)族原子替位掺杂单层WSeTe会发生本征半导体-p (n)型半导体的转变, Ti, V原子替位掺杂单层WSeTe会发生半导体-金属的转变.由于电荷转移以及氮族原子掺杂时价带顶的能带杂化现象,卤族和氮族非金属元素掺杂时价带顶G点附近的Rashba自旋劈裂强度在同一主族随着掺杂原子原子序数的增大而增大. 3d过渡金属元素掺杂会产生能谷极化和磁性,其中Cr, Mn原子替位掺杂会产生高于100 meV的能谷极化,并且Cr,Mn, Fe元素掺杂在禁带中引入了电子自旋完全极化的杂质能级.研究结果对系统地理解单层WSeTe掺杂模型的性质具有重要意义,可以为基于单层WSeTe的电子器件设计提供理论参考.     

Au-Ni弱铁磁合金的自发磁矩和居里点

x=0.42—0.55的Au_1-xNi_x晶态合金是从液态直接淬火到室温,测量低温下这些合金的磁化曲线(2—70kOe),得到在温度1.5K下的自发磁矩值,并用Arrott-Noakes图线方法确定居里点。首先用Perrier等人提出的最近邻模型计算平均磁矩,和实验结果进行了比较。并提出最及次近邻模型,即考虑到次近邻的影响,假设一个Ni原子的最、次近邻18个原子有11个以上是Ni原子,它就具有和纯Ni一样的磁矩(0.606μ_B),否则磁矩为零,由此模型计算的平均磁矩值和实验结果比较符合。本文还对合金中自旋集团(spincluster)的存在和自旅集团之间的相互作用作了讨论,给出了表示自旋集团之间铁磁相互作用的平均内场μ_BH/k_B的值。 关键词：     

过渡族元素对非晶态Nd_(15)Fe_(79)B_6合金磁性的影响

本文讨论了用熔态急冷法制备的非晶态Nd_(15)Fe_(79)B_合金中,掺杂Nb,V,Cr,Mn,Co,Ni和Cu等元素后,对磁矩、居里温度及晶化温度的影响。还用穆斯堡尔谱估计了掺杂后样品内场的变化,并作了合理的解释。     

非晶态Fe86M4Zr10合金的磁性和电性

本文研究了非晶态Fe₈₆M₄Zr₁₀(M=V,Cr,Mn,Fe,CO,Ni,Cu,B,Si)合金的基本磁性和低温电性,讨论了不同元素M的掺杂对FeZr合金居里温度和磁矩的影响,并用相干交换散射模型解释了样品在居里温度附近出现的电阻率极小。 关键词：     

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     

合金元素对钢中NbC异质形核影响的第一性原理研究

为了探索不同合金元素对Nb C异质形核的影响,本文利用第一性原理研究了合金元素X(X=Cr,Mn,Mo,W,Zr,V,Ti,Cu和Ni)对ferrite(100)/Nb C(100)界面性质的影响,并且分析了上述合金元素掺杂前后界面的黏附功、界面能和电子结构.研究结果表明,Cr,V和Ti掺杂的界面具有负的偏聚能,说明它们容易偏聚到ferrite/Nb C界面,但Mn,W,Mo,Zr,Cu和Ni却难以偏聚到此界面.当Mn,Zr,Cu和Ni取代界面处的Fe原子后,界面的黏附强度降低,即这些合金减弱铁素体在Nb C上的形核能力.然而Cr,W,Mo,V和Ti引入界面后,其黏附功比掺杂前的界面要大,且界面能均降低,即提高了界面的稳定性.因此,W,Mo,V和Ti,尤其是Cr,能够有效地促进铁素体形核和细化晶粒.电子结构分析表明,Zr和Cu引入界面后,界面处的Zr,Cu原子和C原子的相互作用变弱;然而Cr和W引入界面后,Cr,W和C原子之间形成了很强的非极性共价键,提高了ferrite/Nb C界面的结合强度.     

Electronic structure and half-metallicity in Heusler alloys Fe2YB (Y=Ti, V, Mn, Cr)

The electronic structure and magnetic properties of B-based Heusler alloys Fe₂YB (Y=Ti, V, Cr and Mn) have been studied theoretically. These alloys are all ferrimagnets except for Fe₂VB. The latter has 24 valence electrons and is a paramagnetic semimetal. Fe₂CrB is predicted to be half-metals at equilibrium lattice constant. The spin polarization of Fe₂MnB is also quite high. The calculated total moments are 1.00 μ_B for Fe₂CrB and 2.04 μ_B for Fe₂MnB. In Fe₂CrB and Fe₂MnB, the total moments are mainly determined by the partial moment of Cr or Mn. The Fe moment is relatively small and antiparallel to that of Cr or Mn. Under uniform lattice distortion, the half-metallicity of Fe₂CrB is more stable than Fe₂MnB, which is related to the detailed DOS structure of them near E_F.     

Magnetic moments in heusler alloys

The Heusler alloys are a series of local moment ferromagnets of composition X₂MnY, with a magnetization of ～4mu_B per Mn atom. Magnetic measurements on the alloy series Ni₂Mn_xT_1?xSn, where T is Ti, V or Cr, indicate that the T site moment changes from ?mu_B (for Ti), through zero (for V), to ⁺mu_B (for CR). A simple physical interpretation is proposed for this sign change in the present work. This approach facilities the interpretation of several other features observed in Heusler alloys.     

Electronic structure of amorphous Zr based alloys with V,Cr and Mn studied by photoelectron spectroscopy and bandstructure calculations

The electronic structure of the amorphous alloys V₃₆Zr₆₄, Cr₃₀Zr₇₀ and Mn₃₀Zr₇₀ has been studied by photoelectron spectroscopy (UPS, XPS) and bandstructure calculations for the ordered analogs. The valence band photoelectron spectra and the calculated density of states reveal a large contribution to the state density at the Fermi level from the 3d metal. This behavior is characteristic of Zr based alloys with early 3d transition metals and differs from alloys with higher 3d electron numbers in which the 3d band is located at higher energies. The implications of the high density of states at E_F of the amorphous Zr-(V, Cr, Mn) alloys for magnetism and the occurrence of superconductivity is discussed.     

Effect of low-valent atom substitution on electronic structure and magnetic properties of Fe1.5M0.5CoSi (M=V, Cr, Mn, Fe) Heusler alloys

Quaternary Heusler alloys Fe_1.5M_0.5CoSi with M=V, Cr, Mn and Fe have been investigated theoretically and experimentally. All of these samples crystallize in the ordered Heusler-type structure. The calculated electronic structure shows a pseudogap around E_F in the minority spin states of Fe₂CoSi. With the substitution of low-valent atoms for Fe, the majority antibonding peak is shifted to higher energy and a minority gap around the Fermi level is opened. High spin polarization ratio is obtained in Fe_1.5M_0.5CoSi (M=V, Cr, Mn) alloys. The calculated total spin moments decrease with decreasing number of valence electrons and follow the Slater-Pauling curve, which agree with the experimental results well. The Curie temperature decreases as M atom varies from Fe to V, but is always higher than 650 K, which is suitable for technical applications.     

Band structure calculations for Heusler phase Co2YBi and half-Heusler phase CoYBi (Y=Mn, Cr)

We have studied the electron structure and magnetic properties of Heusler phase Co₂YBi and half-Heusler phase CoYBi (Y=Mn, Cr) by using the full-potential linearized-augmented plane-wave (FLAPW) method. Co₂MnBi and Co₂CrBi are predicted to be half-metallic magnetism with a total magnetic moment of 6 and 5 μ_B, respectively, well consistent with the Slater-Pauling rule. We also predict CoMnBi to be half-metallic magnetism with a slight compression. The gap origin for Co₂MnBi and Co₂CrBi is due to the 3d electron splitting of Mn (Cr) and Co atoms, and the gap width depends on Co electron splitting. The atom coordination surroundings have a great influence on the electron structure, and consequently the Y site in the X₂YZ structure has a more remarkable electron splitting than the X site due to the more symmetric surroundings. The investigation regarding the lattice constant dependence of magnetic moment shows that the Co magnetic moment exhibits an opposite behavior with the change of the lattice constant for Heusler and half-Heusler alloys, consequently leading to the different variation trends for total magnetic moment. The variation of total and atom magnetic moment versus lattice constant can be explained by the extent of 3d electron splitting and localization of Mn (Cr) and Co atoms for both the series of alloys.     

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     

Muon hyperfine fields in iron and its dilute alloys

The temperature dependence (240 to 633 K) of the interstitial magnetic field, B_μ, as determined by the rotation of the spin of the μ⁺, has been measured for dilute polycrystalline iron alloys with Mo, Ti and Nb additions. In all cases the behaviours differ from one another and from the Fe(A1) alloys previously studied. B_μ, which is negative with respect to the magnetization, is increased in magnitude by A1 and Mo, and decreased greatly by Ti. The addition of Nb creates a two- phase alloy from which we can assess the role of heterogeneity and/or strain on B_μ in iron. If the temperature dependence of the hyperfine field B_hf extracted from B_μ for Fe(Mo) alloys is interpreted on the model previously used to discuss the Fe(A1) data, we would conclude that the muon is attracted to the Mo atom while repelled by the A1 atoms as the temperature decreases. Measurements giving room temperature values of B_μ for iron alloys with Mn, Cr, V and W taken after annealing above the recrystallization temperature are also reported.     

Half-metallic ferrimagnetism in Full-Heusler alloy Mn2CuMg

In the paper Ab initio electronic structure calculations are applied to study the electronic structure and magnetism properties of a new Mn-based Heusler alloy Mn₂CuMg. We take into account both possible L 2₁ structures (CuHg₂Ti and AlCu₂Mn types). The CuHg₂Ti-type structure is found to be energetically more favorable than the AlCu₂Mn-type structure and presents half-metallic ferrimagnetism. However, the case of exchanging X with Y atoms in generic formula loses its half-metallicity due to the symmetric surroundings. Calculations show that their total spin moment is −1μ_B for a wide range of equilibrium lattice constants and the total spin magnetic moment is attributed mainly to the two Mn atoms, while the Cu atom is almost non-magnetic. A small total spin moment origins from the antiparallel configurations of the Mn partial moments. The CuHg₂Ti-type Mn₂CuMg alloy keeps a 100% of spin polarization of conduction electrons at the Fermi level, thus opening the way to engineer new half-metallic alloys with the desired magnetic properties.