Tuning the electronic and magnetic properties of the Si nanoribbons through dangling bond

Combined with three spin configurations, the effects of the dangling bonds on the electronic and magnetic properties of both zigzag edge and armchair edge Si nanoribbions (ZSiNR and ASiNR) have been investigated systematically by the first-principles calculations in the local spin-density function theory. The dangling bonds at one edge or both edges make ZSiNR to transform from ferromagnetic state of the perfect ZSiNR to antiferromagnetic state. However, the dangling bonds at one edge and both edges make ASiNR to transform from nonmagnetic semiconductor of the perfect ASiNR to ferromagnetic and antiferromagnetic metals, respectively. Furthermore, the magnetic moment of the ferromagnetic state increases for the perfect bare one edge and bare both edges successively for either ZSiNR or ASiNR.     

Analysis of the anomalous Hall effect in a double layer of a ferromagnetic and a normal metal

A new method is suggested to investigate the mechanism of the anomalous Hall effect (AHE) in ferromagnetic metals. Using a double layer of a ferromagnet and a normal metal of increasing thickness one can manipulate the AHE in the ferromagnet without changing the ferromagnet's structure and electronic properties. The conduction electrons from the normal metal carry their drift velocity across the interface into the ferromagnetic film and induce an additional AHE conductance ΔG_xy. Its dependence on the mean free path in the normal metal distinguishes between the side jump and the skew scattering mechanisms for the AHE in the ferromagnet.     

Single-site functional-integral approach to itinerant-electron ferromagnetism II. Thermodynamical property

Thermodynamical properties of ferromagnetic metals are discussed by using the single-site functional-integral method developed recently by the present author. It is shown that the entropy and the specific heat consist of two terms; one is due to the thermal excitations of electrons near the Fermi level, and the other arises from the disordered local magnetic moment. Numerical calculations show a huge specific-heat-peak due to magnetic contributions at the Curie temperature, T_c, and a large electronic specific heat at low temperatures and at T>T_c, which are qualitatively in agreement with experimental data of ferromagnetic metals like iron.     

复杂氧化物中电子相分离的量子调控

复杂氧化物可以呈现出高温超导、庞磁阻以及多铁效应等诸多新奇的物理现象.这类材料中的电荷/自旋/轨道和晶格自由度之间的强耦合相互作用,可以导致多种相互竞争且能量非常接近的电子态的空间共存,这就是电子相分离现象.如果可以将材料的空间尺寸缩小到电子相分离的特征长度,其物理性质甚至电子关联作用本身都会发生根本的变化,从而有可能实现复杂氧化物中的量子调控.本文综述了我们课题组在过去几年中针对复杂氧化物中电子相分离的量子调控取得的进展,内容包括：发现了锰氧化物边缘电子态,通过氧化物微纳加工技术,实现了量子态空间分布的调控,提高了庞磁阻锰氧化物的临界温度;研究了当材料空间尺度小于其电子相分离特征尺度时电子相分离的表现,确定了在电子相分离消失以后体系的磁结构;通过超晶格生长技术调控了材料中的掺杂有序度,对锰氧化物中大尺度的电子相分离的物理机理从实验上给出了解释.     

Spectral function of ferromagnetic 3d metals: a self-consistent LSDA+DMFT approach combined with the one-step model of photoemission

The electronic structure of ferromagnetic 3d-transition metals in the vicinity of the Fermi level is dominated by the spin-polarized d bands. Experimentally, this energy region can be probed in detail by means of angle-resolved ultraviolet photoemission and inverse photoemission. In several earlier studies the measured spectra were described either within a single-particle approach based on the local spin-density approximation including matrix-element effects within the so-called one-step model or by sophisticated many-body approaches neglecting these effects. In our analysis we combine for the first time correlation with matrix-element effects to achieve an improved interpretation of photoemission data from ferromagnetic nickel.     

First-Principles Study of Fe-Doped ZnO Nanowires

Using first-principles theory,we predict magnetic,electronic and optical properties in Fe-doped ZnO nanowires.The results show that ferromagnetic(FM)coupling of...     

Long-time relaxation of the magnetization and tunneling magnetoresistance of granular ferromagnets

Magnetic anisotropy and orientational variance as well as shape diversity of granules largely determine the magnetic properties of granular ferromagnetic metals. The model of magnetically anisotropic ellipsoidal granules explains the glassy nature of the magnetic state of such systems. The relaxation of the magnetization and the magnetoresistance of granular ferromagnetic metals is examined on the basis of this model.     

First principle study of the structural,electronic and magnetic properties of Fe,Co, Ni atomic nanochains encapsulated in single walled and double walled beryllium oxygen nanotubes

By using first-principles calculations within the density function theory, the structural, electronic and magnetic properties of transition metals TM (TM=Fe, Co and Ni) atomic chains wrapped in the single walled and double walled BeO nanotubes are investigated. It is found that all these TM chains @ BeONTs systems are ferromagnetic (FM) and a spin splitting between spin up and down is observed. The high magnetic moment and spin polarization of the TM @ BeONTs systems imply that it can be used as magnetic nanostructure and future applications in permanent magnetism, magnetic recording, and spintronics.     

CH_3CSNH_2钝化对铁磁金属与GaAs界面扩散的影响

通过实验对比 ,研究了CH3CSNH2 钝化对铁磁金属与GaAs界面处As扩散行为的影响 .发现S钝化处理改变了表面As元素的化学环境 ,减弱了As元素向铁磁金属外延层中的扩散现象 ,削弱了As与铁磁金属的反应 ,形成了较窄的反应层 ,并且改善了界面磁性 .初步探讨了S钝化影响As扩散的原因 .     

Effect of Ni and Co impurities on the electronic structure and magnetic properties of BCC iron

A theory of disordered binary alloys A_xB_1−x (A=Ni, Co; B=Fe; x0.06) is used to determine the changes in the electronic structure and magnetic properties of body centered cubic (BCC) iron induced by doping with nickel and cobalt impurities. This approximation is an extension of the cluster-Bethe lattice method, in which we incorporate electronic correlations, itinerant and localized nature of electrons 3d, and both long-range and short-range chemical correlations. The magnetism is described by means of a Hubbard Hamiltonian that in conjunction with Green's functions techniques is used to calculate local densities of electronic states. For it we take an atom in the real lattice and it is joined to a Bethe's lattice with like coordination number. The magnetic moments on sites occupied for A and B atoms are obtained self-consistently. Nickel and cobalt impurities in BCC iron can provide crucial information on the modification of the electronic band structure and magnetic moments from pure Fe. The results obtained are compared with those of both pure Fe and binary alloys of Co–Fe and Ni–Fe, which have been obtained by other authors using methods such as: first-principles electronic structure calculations using the layer Korringa–Kohn–Rostoker (KKR), the full-potential linearized augmented plane wave method, the KKR coherent potential approximation combined with the local-density functional method and by the tight-binding linear-muffin-tin orbitals method, obtained good agree. These results and other that recently we have published indicate to us that our methodology can be a new alternative for calculations of the electronic structure and magnetic properties of impurities and alloys of ferromagnetic transition metals.     

Spin fluctuations and peculiarities of semiconductor-metal electronic transitions in almost ferromagnetic compounds of transition metals

The influence of spin fluctuations on the energy spectra of sp and d current carriers in almost ferromagnetic semiconductors based on compounds of d transition metals is examined. It is shown that because electron spectra split in the fluctuating exchange fields in almost ferromagnetic systems, electronic transitions of the type semiconductor-metal are possible, accompanied by the disappearance of energy gaps in the spectra of the sp and d electrons at various temperatures and by a shift of the chemical potential into the region of allowed energies. A specific analysis of similar electronic transitions is presented, based on the almost ferromagnetic compound FeSi. Fiz. Tverd. Tela (St. Petersburg) 41, 1792–1796 (October 1999)     

CH3CSNH2钝化对铁磁金属与GaAs界面扩散的影响

通过实验对比,研究了CH₃CSNH₂钝化对铁磁金属与GaAs界面处As扩散行为的影响.发现S钝化处理改变了表面As元素的化学环境,减弱了As元素向铁磁金属外延层中的扩散现象,削弱了As与铁磁金属的反应,形成了较窄的反应层,并且改善了界面磁性.初步探讨了S钝化影响As扩散的原因. 关键词： S钝化 半导体界面 电子结构 磁性     

半金属磁性材料研究进展

半金属材料是一种新型的功能自旋电子学材料，是一种具有特殊能带结构的物质，近年来13益受到人们的关注。半金属材料从微观上具有导体和绝缘体双重性质：对一种自旋取向的电子其能带结构呈现金属性，而另一自旋取向的电子其能带结构呈现绝缘体性．文章着重对Half—Heusler结构半金属材料、CrO2铁磁半金属、Fe3O4亚铁磁材料半金属、反铁磁材料半金属和钙钛矿及双钙钛矿半金属的结构特性进行分析和综述，并对半金属材料的应用原理和应用前景作了阐述。     

Ab initio study on nonmetal and nonmagnetic metal atoms doped arsenene

The structural, electronic, and magnetic properties of arsenene doped with a series of nonmetals (B, C, F, N, and O) and nonmagnetic metals (Al, Ga, Li, Mg, and Na) are investigated using density functional theory. Magnetism is observed in the case of C. Among all the cases, the C-doped system is the most stable formed system. Hence, we study the ferromagnetic interaction in two-C-doped arsenene. Interestingly, both nonmagnetic (NM) and antiferromagnetic (AFM) states have been observed. As the increasing C?C distance, the magnetic coupling between the moments induced by two C is found to be AFM and the origin of the coupling can be attributed to the p?p hybridization interaction involving polarized electrons.     

Magnetization reversal and spin accumulation in nonmagnetic metals by spin injection from lateral Co/Cu,Co/Al heterojunctions

We have fabricated ferromagnetic/nonmagnetic (FM/NM) metal heterojunctions for the detection of the spin accumulation effect in different nonmagnetic metals. To understand the effect of spin accumulation in more detail, the switching behavior of the ferromagnetic wires was studied by means of magnetoresistance (MR) measurements and Monte Carlo simulations (MC). The polycrystalline heterojunctions were prepared by high-resolution electron beam lithography (HR-EBL) and a special oblique evaporation technique. The ferromagnetic (FM) and the nonmagnetic (NM) metal were evaporated on top of each other in a single-evaporation step to achieve an interface between the two metals of high quality. To verify the quality of the interface, we measured the spin accumulation effect in nonmagnetic copper (Cu) and aluminum (Al) and determined the spin polarization of the current at the interface between the ferromagnetic and nonmagnetic metals.     

Measurement of electronic structure in van der Waals ferromagnet Fe5-xGeTe2

As a van der Waals ferromagnet with high Curie temperature, Fe_5-xGeTe₂ has attracted tremendous interests recently. Here, using high-resolution angle-resolved photoemission spectroscopy (ARPES), we systematically investigated the electronic structure of Fe_5-xGeTe₂ crystals and its temperature evolution. Our ARPES measurement reveals two types of band structures from two different terminations with slight k_z evolution. Interestingly, across the ferromagnetic transition, we observed the merging of two split bands above the Curie temperature, suggesting the band splitting due to the exchange interaction within the itinerant Stoner model. Our results provide important insights into the electronic and magnetic properties of Fe_5-xGeTe₂ and the understanding of magnetism in a two-dimensional ferromagnetic system.     

Modulation effects of Cu doping on magnetic properties of Zn(Ni)O: First-principle calculations

Based on the density functional theory, we explore the electronic and magnetic properties of (Ni,Cu)-codoped ZnO systems (Zn(Ni,Cu)O). It is shown that dopant Cu has a long-range modulation for the Ni-Ni ferromagnetic coupling and enhances the stability of ferromagnetism. Furthermore, we demonstrate that the path of Cu modulation is through the Cu-Ni magnetic interaction.     

Characterization of a Pd-Fe bimetallic model catalyst

Small bimetallic Pd-Fe particles supported on a well ordered alumina film grown on NiAl (1 1 0) were studied focusing on the geometric, electronic, adsorption, as well as magnetic properties. The morphology, growth mode and surface composition were investigated by combining scanning tunneling microscopy (STM), temperature-programmed desorption (TPD) and infrared spectroscopy (IRAS) using CO as a probe molecule. Information on the electronic properties of the bimetallic systems was obtained by means of X-ray photoelectron spectroscopy (XPS). These measurements were amended by in situ ferromagnetic resonance spectroscopy to address the magnetic properties of the bimetallic particles. The subsequent deposition of the metals at 300 K varying the order of metal deposition resulted in two distinct bimetallic systems. Pd deposited on existing Fe particles forms a shell, however, FMR and XPS suggest that intermixing of Pd and Fe occurs to some extent. For the reverse order, a larger amount of Fe is required to coat Pd particles, due to the strong tendency of Pd to segregate to the surface of the particles.     

Formation of stable nanowires from ferromagnetic metals using 2-butyne-1,4-diol

We mechanically fabricated Fe, Co, and Ni nanowires showing conductance quantization under electrochemical potential control. The effects of 2-butyne-1,4-diol and saccharin on the stability of the nanowires were investigated by measuring the conductance and the stretched length of the nanowires. Nanowires of these ferromagnetic metals were stabilized by adding 2-butyne-1,4-diol. In Co, a monoatomic contact was stretched 0.4 nm in length, indicating the formation of a highly stable monoatomic contact of ferromagnetic metals. The improved stability of the nanowires could originate from specific adsorption of organic molecules on the contacts. Mechanical properties of these metals were considered to explain the origin of the metal-dependent stability of the nanowires.