化合物SmCo5的电子结构、自旋和轨道磁矩及其交换作用分析

用自旋极化的MS-Xα方法研究了稀土-过渡族化合物SmCo5₅的电子态密度、自 旋能级劈裂及原子磁矩.研究结果显示，由于化合物中Sm-Co间的轨道杂化效应，使Sm原子原来的5d00空轨道上占据了少量5d电子.由于Co(3d)-Sm(5d)电子间的直接交换作用，导致了Sm-Co间的磁性交换耦合，这是化合物中形成Sm-Co铁磁性长程序的一个重要原因.在SmCo5_{5化合物中存在6个能级呈现负交换耦合，导致了SmCo55化 关键词： 电子结构 自旋极化 原子磁矩 交换耦合}     

NiFe/Mo多层膜界面的电子显微学研究

用高分辨电子显微学方法研究了Ni₈₀Fe₂₀/Mo磁性多层膜，结果表明：(1)多层膜的结晶状态，随Mo非磁性层厚度而变化.当Mo层厚度为0.7nm时，多层膜基本为非晶；当Mo层厚度大于1.6nm时，Mo层和NiFe层内分别结晶为体心立方和面心立方多晶，层内晶粒尺寸为2—6nm.(2)在Mo层厚度为1.6和2.1nm的多层膜中，NiFe层和Mo层之间存在两种取向关系：(110)_Mo∥(111)_NiFe,［111］_关键词：     

Cr-Co-Ga Heusler合金新材料探索和物性研究

通过实验和计算研究了从Co₂CrGa到Cr₂CoGa一系列渐变成分合金(Co_50-xCr_x+25Ga₂₅,x=0—25) 的结构、磁性及输运性质.当Cr不断替代A位Co时,晶体结构逐渐从典型的L2₁结构过渡到Hg₂CuTi结构,晶格常数线性地增大0.69%.合金的磁性从Co_{2 关键词： CrCoGa Hesuler合金 KKR-CPA-LDA计算}     

X-ray properties and interface study of B4C/Mo and B4C/Mo2C periodic multilayers

We present a comparative study of B₄C/Mo and B₄C/Mo₂C periodic multilayer structures deposited by magnetron sputtering. The characterization was performed by grazing incidence X-ray reflectometry at two different energies and high resolution transmission electron microscopy. The experimental results indicate the existence of an interdiffusion layer at the B₄C-on-Mo interface in the B₄C/Mo system. Thus, the B₄C/Mo multilayers were modeled by an asymmetric structure with three layers in each period. The thickness of B₄C-on-Mo interfacial layer was estimated about 1.1 nm. The B₄C/Mo₂C multilayers present less interdiffusion and are well modeled by a symmetric structure without interfacial layers. This study shows that B₄C/Mo₂C structure is an interesting alternative to B₄C/Mo multilayer for X-ray optic applications.     

x射线磁性圆二色吸收谱分析Co膜厚度对原子磁矩和自旋磁矩的影响

利用软x射线磁性圆二色吸收谱(XMCD)研究了Si衬底上沉积的不同厚度的Co膜的轨道磁矩和 自旋磁矩.样品是磁控溅射方法制备的，膜的厚度分别是2nm,10nm和30nm，并在表面覆盖0.8 —1nm厚的金膜防止样品的氧化.根据XMCD求和定则计算得到的轨道磁矩和自旋磁矩分别是0. 249—0.195μ_B(玻尔磁子)和1.230—1.734μ_B.随着膜厚的减小，C o原子的轨道磁矩增加，而自旋磁矩下降.轨道磁矩与总磁矩的比值由0.101上升至0.168，即 2nm膜中Co原子的轨道磁矩对总磁矩的贡献比30nm膜中Co原子的大了83%. 关键词： x射线磁性圆二色 磁性薄膜 轨道磁矩和自旋磁矩 厚度效应     

Local magnetic fields in the Mo layer of Mo/Fe multilayer

Using time-differential perturbed-angular-correlation technique, hyperfine fields at ⁹⁹Tc (←⁹⁹Mo) in the Mo layers in polyimide/Fe (10 nm)/[Mo (t _Mo)/Fe (2.0 nm)]₁₂₀, where t _Mo is in the range between 0.4 and 1.5 nm, were measured at room temperature. The values of the magnetic hyperfine field at the Mo/Fe interface were extracted. Its dependence on the Mo layer thickness suggests that the oscillatory interlayer exchange coupling is due to conduction electron spin polarization in the Mo layer, which in turn is produced via an RKKY-type mechanism.     

Magnetic structure of ErCo10Mo2 and TbCo10Mo2 determined by time-of-flight neutron powder diffraction

The crystal and magnetic structures of tetragonal compounds ErCo₁₀Mo₂ and TbCo₁₀Mo₂ (space group I₄/mmm) have been investigated by time-of-flight neutron powder diffraction at 5 K. The compound ErCo₁₀Mo₂ is planar at 5 K whilst TbCo₁₀Mo₂ remains axial even at low temperatures. The magnetic moments of the three Co sublattices have been determined, with moments of 1.0(0.2)μ _B , 0.8(0.2)μ _B and 0.8(0.2)μ _B for 8i, 8j and 8f sites respectively. The Er and Tb moments are reduced by approximately 7% from their free-ion values by the action of the tetragonal crystal field.     

Co0.9Fe0.1薄膜面内元素分辨的磁各向异性

利用X射线磁性圆二色技术对Co_0.9Fe_0.1薄膜面内元素分辨的磁各向异性进行了研究，通过剩磁模式测量不同磁化方向的样品组分原子单位空穴磁矩的变化，发现除了在生长的磁诱导方向存在易磁化轴外，在与该轴垂直的方向还存在一个类似易轴的软磁化轴；面内的两个难磁化轴与易磁化轴取向大约成66°夹角，从而构成了面内双轴磁各向异性；对不同组分元素，其单位空穴磁矩随磁化方向的变化趋势基本相同，不同磁化方向Fe原子单位空穴的磁矩值约为Co的对应值的87%，反映了Fe原子和Co原子之间存在着强烈的铁磁性耦合. 关键词： 磁各向异性 X射线磁性圆二色 铁磁耦合 CoFe合金薄膜     

Strain-dependent electronic and magnetic of Co-doped monolayer of WSe2

We perform first-principles calculation to investigate electronic and magnetic properties of Co-doped WSe₂ monolayer with strains from −10% to 10%. We find that Co can induce magnetic moment about 0.894 μ_B, the Co-doped WSe₂ monolayer is a magnetic semiconductor material without strain. The doped system shows half-metallic properties under tensile strain, and the largest half-metal gap is 0.147 eV at 8% strain. The magnetic moment (0.894 μ_B) increases slightly from 0% to 6%, and jumps into about 3 μ_B at 8% and 10%, which presents high-spin state configurations. When we applied compressive strain, the doped system shows a half-metallic feature at −2% strain, and the magnetic moment jumps into 1.623 μ_B at −4% strain, almost two times as the original moment 0.894 μ_B at 0% strain. The magnetic moment vanishes at −7% strain. The Co-doped WSe₂ can endure strain from −6% to 10%. Strain changes the redistribution of charges and magnetic moment. Our calculation results show that the Co-doped WSe₂ monolayer can transform from magnetic semiconductor to half-metallic material under strain.     

First-principles study on the electronic structure and the ferromagnetic properties of the cyano-bridged bimetallic compound Mn2(H2O)5Mo(CN)7·4H2O (α phase)

First-principles calculations have been performed to study the electronic structure and the ferromagnetic properties of the cyano-bridged bimetallic compound Mn₂(H₂O)₅Mo(CN)₇·4H₂O (α phase).The calculations were based on density-functional theory and the full potential linearized augmented plane wave method (FP-LAPW). The calculated total energies revealed that the compound has a stable ferromagnetic (FM) ground state, which is in agreement with the experiments. The electronic structure of the compound has a half-metallic behavior. The calculated magnetic moment per molecule is about 15.000 μ_B, the magnetic moment are mainly from Mo and Mn atoms with d electronic configuration. It is also found that there exists ferromagnetic interaction between low-spin Mo²⁺ and high-spin Mn³⁺ ions through the Mo-C-N-Mn linear linkages.     

Electronic structure and magnetic properties of metastable SmCo<Subscript>7</Subscript> compound

The electronic density of states, spin-splittings and atomic magnetic moments of SmCO₇-compound have been studied using spin-polarized MS-Xα method. The results show that a few of electrons are transferred to Sm(5d⁰) orbital because of orbital hybridization between Sm and Co atoms in the compound. The exchange interactions between 3d and 5d electrons lead to the magnetic coupling between Sm and Co, and therefore, result in the long-range ferromagnetic order inside the SmCo₇ compound. There are negative exchange couplings occurring at some levels, which weakens the strength of average coupling around Co lattice. So, the Curie temperature and Co-moment of SmCo₇-decrease distinctly compared with pure Co. Compared with SmCo₅ compound, the disordered substitution of Co-Co “dumbbell-atom” pairs for Sm changes the local environment of Co lattice, which makes the 2e site bear negative magnetic moment. The strength of hybridization near Fermi level weakens and the free energy of the compound increases obviously. Thus, SmCo₇ is a metastable compound at room temperature. Considering the localization of 4f electrons and a few of 5d electrons arising from the orbital hybridization, the magnetic moment of Sm atom will be 1.61μ_B in SmCo₇ compound, which is in agreement with the experimental values of Sm³⁺ ion-moment and Sm atom-moment in metals.     

Mössbauer study of magnetic Fe/FeSi multilayers

Many useful properties of magnetic multilayers depend on the coupling between the ferromagnetic layers. The coupling often oscillates with the thickness of non-magnetic spacer layers: it is ferro- or antiferromagnetic or even non-collinear near a critical thickness. We investigated the magnetron-sputtered Fe/FeSi multilayers with spacer thickness around 1.7 nm by means of Conversion Electron Mössbauer Spectroscopy with oblique incidence of the γ beam in order to gain information on the orientation of the local magnetic moments in the multilayer plane. The results show that the local moments make an angle of 45°–50° with the direction of the remanent magnetization. This is consistent with strong biquadratic coupling which in turn is expected at this spacer thickness from our magnetic measurements. An analysis of the distribution ofB _hf corresponding to different numbers of n.n. Si atoms in the bcc Fe structure points to weak diffusion of Si through the Fe/FeSi interface characterized by a diffusion length of about twice the substrate roughness.     

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.     

Electronic structure and magnetic properties of the N monodoping and (Li, N)-codoped ZnO

Using first-principles calculations based on density functional theory, we investigated systematically the electronic structures and magnetic properties of N monodoping and (Li, N) codoping in ZnO. The results indicate that monodoping of N in ZnO favors a spin-polarized state with a magnetic moment of 0.95 μ_B per supercell and the magnetic moment mainly comes from the unpaired 2p electrons of N and O atoms. In addition, it was found that monodoping of N in ZnO is a weak ferromagnet and it is the spin-polarized O atoms that mediate the ferromagnetic exchange interaction between the two N atoms. Interestingly, by Li substitutional doping at the cation site (Li_Zn), the ferromagnetic stability can be increased significantly and the formation energy can be evidently reduced for the defective system. Therefore, we think that the enhancement of ferromagnetic stability should be attributed to the accessorial holes and the lower formation energy induced by Li_Zn doping.     

Investigations of cobalt and carbon codoping in gallium nitride for spintronic applications

Extensive theoretical investigations have been carried out to study the ferromagnetic properties of transition metal doped wurtzite GaN using the Tight Binding Linear Muffin-tin Orbital (TBLMTO) method within the density functional theory. The present calculation reveals ferromagnetism in cobalt doped GaN when one gallium is replaced by cobalt in a 3×3×2 supercell of GaN, which gives rise to a cobalt concentration of 2.77%. The system is half-metallic with a magnetic moment of 4.0 μ_B. When Co is bonded with one carbon, there is a drastic decrease in magnetic moment and the system becomes metallic. When Co dimer is introduced via nitrogen which corresponds to the Co concentration of 5.5% the magnetic moment is 3.99 μ_B and the system is half-metallic. Same trend is observed when Co is bonded via nitrogen with unequal distance. When cobalt dimer is formed via carbon, the moment becomes 2.95 μ_B and it shows metallic character. For dimer via carbon with unequal distance, the moment is 3.0 μ_B and the system becomes semiconductor. For higher percentage of cobalt dopant the system shows metallic character. C and Co doped GaN samples have been synthesized experimentally and characterized with X-ray diffraction, transmission electron microscopy, micro-Raman and superconducting quantum interface device measurements. The observed results are correlated with the theoretical studies.     

Interlayer Exchange Coupling Across Quasi-Amorphous Ti-Co and Zr-Co Spacers

Co/Ti and Co/Zr multilayers with wedge-shaped and constant-thickness Ti and Zr sublayers were prepared using UHV DC/RF magnetron sputtering. Results showed that the Co sublayers are ferromagnetically coupled up to Ti and Zr spacer thickness of about 1.9 and 2.4 nm, respectively. Furthermore, a weak antiferromagnetic coupling of the Co sublayers was observed for a Ti (Zr) thickness range between 1.9 and 2.7 nm (2.4 and 3.2 nm). The Co sublayers are very weakly exchange coupled or decoupled for d _Ti 2.7 nm and d _Zr 3.2 nm. The rapid decrease of the interlayer exchange coupling could be explained by its strong damping due to formation of a non-magnetic quasi-amorphous Ti-Co and Zr-Co alloy layer at the interfaces.     

Interface characteristics of Mo/Si and B4C/Mo/Si multilayers using non-destructive X-ray techniques

A methodology combining non-destructive X-ray techniques is proposed to study the interfacial zones of periodic multilayers. The used X-ray techniques are X-ray emission spectroscopy induced by electrons and X-ray reflectivity in the hard and soft X-ray ranges. The first technique evidences the presence of compounds at the interfaces and gives an estimation of the thickness of the interfacial zone. These informations are used to constrain the fit of the X-ray reflectivity curves that enables to determine the thickness and roughness of the various layers of the stacks. The results are validated in the soft X-ray range where the reflectivity curves are very sensitive to the chemical state of the elements present in the stack. The methodology is applied to characterize Mo/Si (1-4 nm/2 nm) and B₄C/Mo/Si (1 nm/2 nm/2 nm) multilayers. It is shown that the two interfacial zones of the Mo/Si multilayers are composed of the silicides MoSi₂ and Mo₅Si₃. It is found that the interface thickness is about to be 0.4-0.8 nm depending on the samples. The molybdenum silicides are also evidenced at the interfaces of the B₄C/Mo/Si multilayers. However, their interface thickness is 0.2 nm thinner than that of the same stack without the B₄C layers, these layers being at the Mo-on-Si side or at the Si-on-Mo side. Thus, the B₄C layers do not stop but only reduce the interdiffusion between the Mo and Si layers.     

The structure and magnetism of Fe/Mo(0 0 1) surface: A pseudopotential calculation

The effect of structure on the magnetism of iron monolayers (MLs) on molybdenum is investigated using the density functional theory (DFT) with norm conserving pseudopotentials and a plane wave basis, under the local spin density approximation (LSDA). Relaxation of 5 and 7 ML of Mo resulted in a contraction of 11.3% and 11.7%, respectively, for the top Mo–Mo interlayer spacing in close agreement with experimental results. In the case of one Fe overlayer, the top Fe–Mo interlayer spacing contracted by 15.8% for a ferromagnetic (FM) p(1×1) and 20.6% for an antiferromagnetic (AF) c(2×2) configuration. The magnetic moment of the surface (Fe) layer is enhanced from its theoretically calculated bulk value. Total energy calculations show that the AF c(2×2) is the stable state with a magnetic moment of 2.53 μ_B. The surface Fe atoms are AF coupled with each other and with the Mo layers below, showing layered AF coupling. The present study demonstrates the reliability of the pseudopotential approach under LSDA with core corrections included to the calculation of magnetic properties of combined transition metal systems.     

Magnetic properties of Ni doped gallium nitride with vacancy induced defect

Investigations have been carried out to study the ferromagnetic properties of transition metal (TM) doped wurtzite GaN from first principle calculations using tight binding linear muffin-tin orbital (TBLMTO) method within the density functional theory. The present calculation reveals ferromagnetism in nickel doped GaN with a magnetic moment of 1.13 μ_B for 6.25% of Ni doping and 1.32 μ_B for 12.5% of nickel doping, there is a decrease of magnetic moment when two Ni atoms are bonded via nitrogen atom. The Ga vacancy (V_Ga) induced defect shows ferromagnetic state. Here the magnetic moment arises due to the tetrahedral bonding of three N atoms with the vacancy which is at a distance of 3.689 Å and the other N atom which is at a distance of 3.678 Å .On the other hand the defect induced by N vacancy (V_N) has no effect on magnetic moment and the system shows metallic character. When Ni is introduced into a Ga vacancy (V_Ga) site, charge transfer occur from the Ni ‘d’ like band to acceptor level of V_Ga and formed a strong Ni–N bond. In this Ni–V_Ga complex with an Ni ion and a Ga defect, the magnetic moment due to N atom is 0.299 μ_B .In case of Ni substitution in Ga site with N vacancy, the system is ferromagnetic with a magnetic moment of 1 μ_B.     

On the interpretation of NMR experiments in CoGa alloys

We show that in Co_xGa_1?x alloys NMR data reported by Grover et al. in combination with existing magnetization data can be interpreted as follows. The group of atoms consisting of a Co antistructure atom and its eight nearest neighbours behaves as a magnetic entity. The (saturation) magnetic moment of the anti-structure atom (?1.6μ_B) is much larger than the corresponding moment on a neighbouring Co atom (?0.16 μ_B).