Magnetic properties of 3d transition metal monolayers on metal substrates

We report results of systematic calculations for magnetic properties of 3d transition metal monolayers on Pd(001) and Ag(001). We find large similarities to interactions of magnetic 3d impurities in the bulk. Therefore the overlayer results are supplemented with results for 3d dimers in Cu, Ag, and Pd. Differences between the two classes of systems are utilized to reveal the interaction within the overlayers and between overlayers and substrates. In virtually all cases we find both ferromagnetic and antiferromagnetic solutions, showing large magnetic moments and similar densities of states. From the trend of the calculations we conclude that V, Cr, and Mn overlayers favor the antiferromagnetic c(2×2) structure, while Ti, Fe, Co, and Ni prefer the ferromagnetic one.     

Site preference and elastic properties of ternary alloying additions in B2 YAg alloys by first-principles calculations

First-principles calculations were preformed to study the site preference behavior and elastic properties of 3d (Ti–Cu) transition-metal elements in B2 ductility YAg alloy. In YAg, Ti is found to occupy the Y sublattice whereas V, Cr, Co, Fe, Ni and Cu tend to substitute for Ag sublattice. Due to the addition of 3d transition metals, the lattice parameters of YAg is decreased in the order: V<Cu<Cr<Ni<Co<Fe<Ti. The calculated elastic constants show that Cr, Fe, Co and Cu can improve the ductility of YAg alloy, and Fe is the most effective element to improve the ductility of YAg, while Ti, Ni and V alloying elements can reduce the ductility of YAg alloy, especially, V transforms ductile into brittle for YAg alloy. In addition, both V and Ni alloying elements can increase the hardness of YAg alloy, and Y₈Ag₇V is harder than Y₈Ag₇Ni.     

Galvanomagnetic properties of Heusler alloy Co<Subscript>2</Subscript><Emphasis Type="Italic">Y</Emphasis>Al (<Emphasis Type="Italic">Y</Emphasis> = Ti,V, Cr,Mn, Fe,and Ni)

The Hall effect and the magnetoresistance of ferromagnetic Heusler alloys Co₂ YAl, where Y = Ti, V, Cr, Mn, Fe, and Ni have been studied at T = 4.2 K in magnetic fields H ≤ 100 kOe. Normal R ₀ and anomalous R _S Hall coefficients are shown to be maximal in magnitudes in the middle of the 3d period of the periodic table of elements. Coefficient R ₀ changes the negative sign to positive sign in going from weak (Y = Ti, V) to strong (Y = Cr, Mn, Fe, and Ni) ferromagnetic alloys. Constant R _S is positive and proportional to ρ^2.9 in all the alloys. The magnetoresistance of the alloys is not higher than several percent and its magnitude is changed fairly significantly in the dependence on the number of valence electrons z; the magnetoresistance signs vary arbitrarily.     

Coverage-dependent magnetization of 3d transition-metal adatoms on Co(0 0 1) in the submonolayer regime

The electronic structure of 3d transition-metal atoms on face-centered cubic Co(0 0 1) substrate is determined within ab initio density functional calculations in the gradient corrected approach. Calculations are performed for ordered surface configuration with coverage equal to 0.25, 0.5, 0.75 and 1 ML. For Ni and Fe a ferromagnetic coupling with the Co atoms is always obtained independently of the concentration. Moreover the values of the magnetic moments remain similar. For Mn a ferromagnetic coupling is obtained for low-coverage whereas an in-plane antiferromagnetic coupling is found for a complete Mn overlayer on Co(0 0 1). Also, for Sc, Ti, V and Cr a drastic modification of the magnetic map is observed when we go from low-coverage to the monolayer. Cr (Mn) adatoms present antiferromagnetic (ferromagnetic) coupling with Co(0 0 1) for x = 0.25 whereas an in-plane antiferrimagnetic coupling is obtained for x = 1.00.     

Specific features of the electrical resistivity of half-metallic ferromagnets Fe2MeAl (Me = Ti,V, Cr,Mn, Fe,Ni)

The transport properties of half-metallic ferromagnetic Heusler alloys Fe₂MeAl (where Me = Ti, V, Cr, Mn, Fe, and Ni are 3d transition elements) have been measured in the temperature range of 4–900 K. The specific features in the behavior of the electrical resistivity have been considered in terms of the two-current conduction model, which takes into account the presence of an energy gap in the electron spectrum of the alloys near the Fermi level.     

Full-Heusler合金X2YGa(X=Co,Fe,Ni;Y=V,Cr,Mn)的电子结构、磁性及半金属特性的第一性原理研究

利用基于密度泛函理论的全势线性缀加平面波方法,结合广义梯度近似,对full-Heusler X₂YGa(X=Co,Fe,Ni;Y=V,Cr,Mn)合金的电子结构、磁性及半金属特性进行了研究,并讨论了自旋-轨道耦合作用对它们的影响.计算结果表明,自旋-轨道耦合作用对full-Heusler X₂YGa(X=Co,Fe,Ni;Y=V,Cr,Mn)合金的电子结构,磁性与半金属特性的影响很小. 当未考虑自旋-轨道耦合作用时,Co₂VGa,Co₂CrGa,和Fe₂CrGa合金为半金属或准半金属铁磁体,加入自旋-轨道耦合作用后体系的自旋极化率将降低1%左右, 它们依然保持很高的自旋极化率.Fe₂MnGa,Co₂MnGa,Ni₂CrGa和Ni₂MnGa合金为一般铁磁体,Fe₂VGa和Ni₂VGa合金为顺磁体. 关键词： 半金属特性 自旋-轨道耦合 Heusler合金 全势线性缀加平面波方法(FLAPW)     

High-field magnetization of band ferromagnets Co<Subscript>2</Subscript><Emphasis Type="Italic">Y</Emphasis>Al (<Emphasis Type="Italic">Y</Emphasis> = Ti,V, Cr,Mn, Fe,Ni)

The temperature dependences of the magnetization of ferromagnetic Heusler alloys Co₂ YAl, where Y = Ti, V, Cr, Mn, Fe, and Ni have been studied at H = 50 kOe in the range 2 K < T < 1100 K. It is shown that the high-field (H ≥ 20 kOe) magnetization is described within the Stoner model.     

Spin‐polarized electron gas in Co2M Si/SrTiO3 (M = Ti,V, Cr,Mn, and Fe) heterostructures

Spin‐polarized density functional theory is used to study the TiO₂ terminated interfaces between the magnetic Heusler alloys Co₂Si (M = Ti, V, Cr, Mn, and Fe) and the non‐polar band insulator SrTiO₃. The structural relaxation at the interface turns out to depend systematically on the lattice mis‐ match. Charge transfer from the Heusler alloys (mainly the M 3d orbitals) to the Ti d_xy orbitals of the TiO₂ interface layer is found to gradually grow from M = Ti to Fe, resulting in an electron gas with increasing density of spin‐polarized charge carriers. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

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     

Antiferromagnetism of the α-Mn system

The variation of the Néel temperature (T_N) of antiferromagnetic alloys of Mn with 3-d elements has been studied by electrical resistivity measurements. Binary Mn-rich alloys Fe, Co, Ni, Ti, Rh, Os, Ir, and Ru were investigated. The results show a strong and systematic dependence on the number of d-electrons of the impurity element. Elements with more d electrons than Mn raise T_N, while those with fewer d electrons depress T_N. The change of T_N per atomic percent impurity also exhibits a striking, non-monotonic dependence on the impurity used. The dependence shows inversion symmetry with impurities around Mn.To further elucidate the properties of the Mn-rich antiferromagnetic system, a study was made of ternary Mn-rich alloys in the MnFeCr, MnCoNi, and MnVTi systems. The results from the MnFeCr system are consistent with the rigid-band model, the average number of d-electrons per atom being of primary importance determiningh the antiferromagnetism in this system.Our goal in these studies has been to provide a firm experimental data baseupon which future theoretical work can be built. A more detailed understanding of the very intriguing α-Mn magnetic system now awaits further theoretical investigation.     

TM掺杂的Ⅲ-Ⅴ族稀磁半导体电磁性质的第一原理计算

使用基于自旋局域密度泛函理论的第一性原理方法对3d过渡金属(TM=V，Cr，Mn，Fe，Co和Ni)掺杂的Ⅲ-Ⅴ族半导体(GaAs和GaP)的电磁性质进行了计算.结果发现：用V，Cr和Mn掺杂时体系将出现铁磁状态，而Fe掺杂时将出现反铁磁状态，Co和Ni掺杂时，其磁性则不稳定.其中，Cr掺杂的GaAs和GaP将可能是具有较高居里温度的稀磁半导体(DMS).在这些DMS系统中，V离子的磁矩大于理论期待值，Fe，Co和Ni离子的磁矩小于理论期待值，Cr和Mn离子的磁矩与期待值的差距取决于晶体的对称性以及磁性离子的能带分布.此外，使用Si和Mn共同对Ⅲ-Ⅴ族半导体进行掺杂，将有利于DMS表现为铁磁状态，并可以使体系的T_C进一步提高. 关键词： 稀磁半导体 过渡金属 掺杂 共掺杂     

Analysis of electronic structures of 3d transition metal-doped TiO2 based on band calculations

The electronic structures of titanium dioxide (TiO₂) doped with 3d transition metals (V, Cr, Mn, Fe, Co and Ni) have been analyzed by ab initio band calculations based on the density functional theory with the full-potential linearized-augmented-plane-wave method. When TiO₂ is doped with V, Cr, Mn, Fe, or Co, an electron occupied level occurs and the electrons are localized around each dopant. As the atomic number of the dopant increases the localized level shifts to lower energy. The energy of the localized level due to Co is sufficiently low to lie at the top of the valence band while the other metals produce midgap states. In contrast, the electrons from the Ni dopant are somewhat delocalized, thus significantly contributing to the formation of the valence band with the O p and Ti 3d electrons. Based on a comparison with the absorption and photoconductivity data previously reported, we show that the t_2g state of the dopant plays a significant role in the photoresponse of TiO₂ under visible light irradiation.     

内掺过渡金属非典型富勒烯M@C22(M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni) 几何结构、电子结构、稳定性和磁性的密度泛函研究

采用密度泛函理论中广义梯度近似对非典型富勒烯C₂₂和过渡金属内掺衍生物M@C₂₂(M=Sc,Ti,V,Cr,Mn,Fe,Co和Ni)的几何结构和电子结构进行计算研究.发现非典型富勒烯C₂₂的基态结构是含有一个四碳环的单重态笼状结构.过渡金属原子的掺入明显提高了体系的稳定性. C-M键既有一定共价性又有一定离子性.磁性、能级图、轨道分布和态密度图分析表明: M原子的3d轨道和碳笼的C原子的原子轨道之间存在较强的轨道杂化. Ti, Cr, Fe和Ni内掺的结构出现磁性完全猝灭现象. Sc和碳笼间是弱反铁磁作用, V,Mn和Co与碳笼间是弱铁磁作用.     

Specific features of the electrical resistivity of half-metallic ferromagnets Co<Subscript>2</Subscript> <Emphasis Type="Italic">Me</Emphasis>Al (<Emphasis Type="Italic">Me</Emphasis> = Ti,V, Cr,Mn, Fe)

The transport properties of half-metallic ferromagnetic Heusler alloys Co₂MeAl (Me = Ti, V, Cr, Mn, Fe are transition 3d metals) have been measured in the temperature range of 4–900 K. The specific features of the behavior of the resistivity have been considered in the framework of the two-current model of conductivity that takes into account the existence of the energy gap in the electronic spectra of the alloys near the Fermi level of one of electron subbands that differs in the spin direction.     

Low-temperature heat capacity upon the transition from paramagnetic to ferromagnetic Heusler alloys Fe<Subscript>2</Subscript> <Emphasis Type="Italic">Me</Emphasis>Al (<Emphasis Type="Italic">Me</Emphasis> = Ti,V, Cr,Mn, Fe,Co, Ni)

The heat capacity of band magnets Fe₂MeAl (Me = Ti, V, Cr, Mn, Fe, Co, Ni) ordered in crystal structure L2₁ has been measured in the range 2 K ≤ T ≤ 50 K. The dependences of the Debye temperature Θ_D, the Sommerfeld coefficient γ, and the temperature-independent contribution to heat capacity C₀ on the number of valence electrons z in the alloys have been determined.     

Study on the oscillatory behaviour of the lattice parameter in ternary iron–nitrogen compounds

The structural properties of the XFe₃N (X=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) cubic ternary iron based nitrides as well as the preferential occupation site of X in the structure were studied using Full Potential Linearized Augmented Plane Wave method, within the Density Functional Theory formalism, Wien2k code, the exchange-correlation potential described with the Perdew–Burke–Ernzerhof expression, based in the Local Spin Density Approximation and Generalized Gradient Approximation. According the calculations, the Sc, Co, Ni, Cu and Zn, atoms preferred the corner sites of the cubes, while Ti, V, Cr and Mn occupy the centre of the faces of the equilibrium structures. The equilibrium structure lattice parameters have an oscillatory behaviour with the atomic number of X, with decreasing amplitude as the atomic number of X increases. This trend do not correlated with the atomic radii of X.     

Carbon nanotube synthesis on catalytic metal alloys in methane/air counterflow diffusion flames

Various morphologies of multi-walled carbon nanotubes (MWNTs) are grown catalytically on metal-alloy probes in counterflow diffusion flames using methane as fuel. Carbon nanotube (CNT) properties and morphologies are investigated as functions of local gas-phase temperatures, C-related species concentrations (e.g. C₂H₂, CO), sampling positions, C₂H₂ adding to the fuel, and metal-alloy compositions (i.e., Fe, Fe/Cr, Ni/Cu, Ni/Ti, Ni/Cr, Ni/Cr/Fe). MWNTs grow optimally in non-sooty regions of the flames. C₂H₂ addition is found to promote direct synthesis of vertically well-aligned MWNTs with uniform diameters from Ni/Cr/Fe and Ni/Ti alloys.     

First-principles linear muffin-tin orbital investigations in the electronic and magnetic structures of double perovskites Ba2TMoO6 (T=V,Cr, Mn,Fe and Co)

The electronic and magnetic structures of ordered double perovskites Ba₂TMoO₆ (T=V, Cr, Mn, Fe and Co) are systematically investigated by means of the first-principle linear muffin-tin orbitals with the atomic-sphere approximation (LMTO-ASA) method. The calculations are performed by using the both local spin density approximation (LSDA) and the LSDA+U Coulomb interaction schemes. The results show a half-metallic ferrimagnetic ground states for T=Cr, Fe and Co in LSDA+U treatment, whereas half-metallic ferromagnetic character is observed for T=V. For T=Mn, insulating ground state is obtained, stabilized in the antiferromagnetic state. The LSDA+U calculations yield better agreement with the theoretical and the experimental results than do the LSDA.     

Effect on alloying at the Fe/Ni(001) interfaces on the interlayer exchange coupling

We investigate the stability of various ordered FeNi alloys at the interfaces of Fe/Ni superlattices by using ab initio density functional calculation. We consider an Fe_0.5Ni_0.5 ordered alloy of one or two monolayers thick at different positions beyond the interface and the possibility of an interdiffusion of a complete monolayer of Ni(Fe) in Fe(Ni) slab. An interfacial atomic layer of Fe_0.5Ni_0.5 exchanged with its adjacent Ni monolayers, leading to a buffer zone of Ni₃Fe composition is found to be the most stable structural configuration. For this atomic arrangement we investigate the magnetic profile and the resulting interlayer exchange coupling between the Ni slabs for Fe spacer thickness of 0 to 4 monolayers.     

Metastable magnetic configurations of (V, Cr, Mn and Fe) on Ir(0 0 1) surfaces

We present a theoretical study of the electronic and magnetic structure of the 3d-transition metals (M = V, Cr, Mn and Fe) in several overlayer systems. The electronic as well as magnetic structures are investigated for pseudomorphic overlayers (M/Ir(0 0 1)), ordered alloyed overlayers of the type M_0.5Ir_0.5/Ir(0 0 1) and ordered binary surface alloys of V, Cr, Mn and Fe transition metals on Ir(0 0 1) substrates. The calculations are performed with a self-consistent tight-binding method using the unrestricted Hartree-Fock approximation within the Hubbard model. We obtained metastable c(2 × 2) configurations for V, Cr and Mn and a p(1 × 1) configuration for Fe pseudomorphic overlayers. However, ferrimagnetic configuration has been obtained for the ordered surface alloys M_0.5Ir_0.5 and the binary alloyed overlayers on Ir(0 0 1) surfaces.