SiC单层内Co空间选位对自旋组态的调控

基于第一性原理的密度泛函理论,对SiC单层不同位置掺杂Co进行了能带结构、电子态密度、净自旋密度和自旋纹理等计算,结果表明不同位置的掺杂引起不同特征的自旋积累及单层的电子结构特性。由于Co的不同选位掺杂而产生一些新奇现象,如扭曲的Co-C键在掺杂SiC内激发了自旋流而诱导了自旋重新分布,不同选位的Co原子通过调整内磁场改变了小极化子内巡游电子的定域属性,增加了Dirac点附近磁振子的色散强度等。这些研究结果为得到一个人工调控量子自旋电路和选频自旋波器件内自旋谷电子提供了理想平台。     

Electron doping induced stable ferromagnetism in two-dimensional GdI3 monolayer

As a two-dimensional material with a hollow hexatomic ring structure, Néel-type anti-ferromagnetic (AFM) GdI₃ can be used as a theoretical model to study the effect of electron doping. Based on first-principles calculations, we find that the Fermi surface nesting occurs when more than 1/3 electron per Gd is doped, resulting in the failure to obtain a stable ferromagnetic (FM) state. More interestingly, GdI₃ with appropriate Mg/Ca doping (1/6 Mg/Ca per Gd) turns to be half-metallic FM state. This AFM−FM transition results from the transfer of doped electrons to the spatially expanded Gd-5d orbital, which leads to the FM coupling of local half-full Gd-4f electrons through 5d−4f hybridization. Moreover, the shortened Gd−Gd length is the key to the formation of the stable ferromagnetic coupling. Our method provides new insights into obtaining stable FM materials from AFM materials.     

HfSe2 monolayer stability tuning by strain and charge doping

Strain and charge doping are the effective ways to modulate the electronic and phonon properties of materials. The effects of biaxial tensile strains and charge dopings on the stabilities of HfSe₂ monolayer have been systematically investigated using first-principles methods. Its two-dimensional Young's modulus is only 65.4 N/m, and it is easy to be stretched. When the tensile strain is applied on HfSe₂ monolayer, two of its phonon modes soften with one frequency decreasing to zero at critical strain. Our results show that electron and hole dopings could suppress the softening of phonon modes, and significantly enhance the ideal strength by 28% and 36%, respectively. The calculations for electronic structures and phonon dispersions provide the theoretical references for future nano-device designing.     

掺杂ZnTe对电子结构与磁性质的影响

为了研究Mn、Fe、Co、Ni掺杂ZnTe的电子结构和磁性的相关性质.本文基于第一性原理的数值基组的方法计算了Mn、Fe、Co、Ni掺杂ZnTe的能带结构、态密度,分析了掺杂结构的稳定性和磁性性质.结果发现Mn、Fe、Co、Ni掺杂ZnTe的杂质替换能分别为-1.14 e V,-1.23 e V,39.95 e V,-4.32 eV,表明Mn、Fe、Ni掺杂的ZnTe在实验上较容易实现.Mn、Co掺杂ZnTe导致体系产生的总磁矩分别为0.997μB,1.103μB,其中磁性的主要来源于Mn、Co原子在Zn位的取代而引起,产生局域磁性主要取决于Mn、Co的d轨道与Te的p轨道耦合作用.     

Magnetism in boron nitride monolayer: Adatom and vacancy defect

Using the full potential linearized augmented plane wave (FLAPW) method, we have investigated the adatom or vacancy defect induced magnetic properties of hexagonal boron nitride (h-BN) monolayer. It has been observed that the N vacancy defect has no influence on the magnetic property of h-BN, whereas the B vacancy defect caused spin polarization in the nearest three N atoms. The total magnetic moment is about 0.87 μ_B within muffin-tin radius (0.29 μ_B per N atom) and the spin polarized N atoms show metallic feature. In the presence of B adatom defect, we have obtained rather weak spin polarization about 0.1 μ_B. However, the sizable magnetic moment of 0.38 μ_B appears in N adatom defect. Both B and N adatom defect systems preserve very close to semiconducting feature with a finite band gap. We have found that the DOS and the XMCD spectral shapes are strongly dependent on the defect type existing in the h-BN monolayer and this finding may help reveal the origin of magnetism in the h-BN layer if one performs surface sensitive experiment such as spin polarized scanning tunneling microscopy or XMCD measurement in the near future.     

Magnetism induced by capping of non-magnetic ZnO nanoparticles

Magnetism of 10 nm size capped nanoparticles, NPs, of non-magnetic ZnO is analysed in terms of the surface band since, as magnetic dichroism analysis has pointed out, impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states. Due to the nanometric scale of the particles the kinetic energy spectrum of the surface states can be considered as discrete. Therefore, the magnetic polarisation cannot be easily induced by pumping electrons to energy levels above the Fermi energy. It is in the Fermi level itself, generally unfilled, that develops a spontaneous magnetic moment similarly to that induced by Hund rules in unfilled atomic orbitals. It is shown, however, that the total magnetic moment of the surface originated at the unfilled Fermi level can reach values as large as 10² or 10³ Bohr magnetons.     

Tuning magnetism of monolayer GaN by vacancy and nonmagnetic chemical doping

In view of important role of inducing and manipulating the magnetism in 2D materials for the development of low-dimensional spintronic devices, the magnetism of GaN monolayer with Ga vacancy and nonmagnetic chemical doping are investigated using first-principles calculations. It is found that pure GaN monolayer has graphene-like structure and is nonmagnetic. While, a neutral Ga vacancy can induce 3 μ_B intrinsic magnetic moment, localized mainly on the neighboring N atoms. Interestingly, after one Mg or Si atom doping in g-GaN with Ga vacancy, the magnetic moment can be modified to 4 μ_B or 2 μ_B respectively due to the change in hole number. Meantime, Mg-doped g-GaN with Ga vacancy shows half-metal character. With the increasing of doping concentrations, the magnetic moment can be further tuned. The results are interesting from a theoretical point of view and may open opportunities for these 2D GaN based materials in magnetic devices.     

铁原子吸附联苯烯单层电子结构的第一性原理

联苯烯单层由碳原子的四元、六元和八元环组成,具有与石墨烯相似的单原子层结构.2021年5月,Science首次报道了该材料的实验合成,引起了科研工作者的极大关注.基于第一性原理的密度泛函方法,研究了铁原子在联苯烯单层的吸附构型并分析了其电子结构.结构优化、吸附能和分子动力学的计算表明,联苯烯单层的四元环空位是铁原子最稳定的吸附位点,吸附能可达1.56 eV.电子态密度计算表明铁3d电子与碳的2p电子有较强的轨道杂化,同时电荷转移计算显示铁原子向近邻碳原子转移的电荷约为0.73个电子,说明联苯烯单层与吸附的铁原子之间形成了稳定的化学键.另外,铁原子吸附于联苯烯单层后体系显磁性,铁原子上局域磁矩大小约为1.81μB,方向指向面外.因此,本文确认了联苯烯单层是比石墨烯更好的铁原子吸附载体且体系有磁性,这为研究吸附材料的电磁、输运、催化等特性提供了新的平台.     

Metal-to-insulator transition in two-dimensional ferromagnetic monolayer induced by substrate

Two-dimensional(2D) ferromagnetic(FM) materials have great potential for applications in next-generation spintronic devices. Since most 2D FM materials come from van der Waals crystals, stabilizing them on a certain substrate without killing the ferromagnetism is still a challenge. Through systematic first-principles calculations, we proposed a new family of 2D FM materials which combines TaX(X = S, Se or Te) monolayer and Al_2O_3(0001) substrate. The TaX monolayers provide magnetic states and the Al_2O_3(0001) substrate stabilizes the former. Interestingly, the Al_2O_3(0001)substrate leads to a metal-to-insulator transition in the Ta X monolayers and induces a band gap up to 303 meV. Our study paves the way to explore promising 2D FM materials for practical applications in spintronics devices.     

Magnetism induced by nonmagnetic dopants in zinc-blende SiC: First-principle calculations

Magnetism induced by the nonmagnetic dopants in the zinc-blende SiC (3C-SiC) is investigated by first-principle calculations. The atoms of the first 20 elements in the periodic table except inert gas are used to replace either Si or C atoms as dopants. We find that some nonmagnetic substitutional dopants (mainly the Group IA, Group IIA, Group IIIB, and Group VIIB elements) prefer the spin-polarized ground states with local magnetic moments. In general, the condition for obtaining the local magnetic moments and the magnetic ground state requires that the dopants are p-type and have large electronegativity difference from the neighboring host atoms. The magnetic moments can be tuned over a range between 1 μ B and 3 μ B by doping with the nonmagnetic elements. The nearest-neighbor exchange couplings J 0 between the local magnetic moments are quite large and the codoping method is proposed to increase the dopant concentration. These imply that the nonmagnetic doping in SiC may exhibit collective magnetism. Moreover, the Group IIA Mg and Ca atoms substituting the preferred Si atoms favor the ferromagnetic ground states with the half-metallic electronic properties, which suggests that Mg or Ca substitutional doping on the Si sites in SiC could be a potential route to fabricating the diluted magnetic semiconductors.     

V,Cr,Mn掺杂MoS2磁性的第一性原理研究

基于第一性原理的自旋极化密度泛函理论分别研究了过渡金属V, Cr, Mn掺杂单层MoS₂的电子结构、 磁性和稳定性. 结果表明: V和Mn单掺杂均能产生一定的磁矩, 而磁矩主要集中在掺杂的过渡金属原子上, Cr单掺杂时体系不显示磁性. 进一步讨论双原子掺杂MoS₂ 体系中掺杂原子之间的磁耦合作用发现, Mn掺杂的体系在室温下显示出稳定的铁磁性, 而V掺杂则表现出非自旋极化基态. 形成能的计算表明Mn掺杂的MoS₂体系相对V和Cr 掺杂结构更稳定. 由于Mn掺杂的MoS₂ 不仅在室温下可以获得比较好的铁磁性而且其稳定性很高, 有望在自旋电子器件方面发挥重要的作用. 关键词： 2')" href="#">单层MoS₂ 掺杂 铁磁态 第一性原理     

Effect of Er3+ doping in SnO2 semiconductor nanoparticles synthesized by solgel technique

Pure and Er³⁺ doped SnO₂ semiconductor nanoparticles have been synthesized by solgel technique. The X-ray diffraction patterns show peaks corresponding to tetragonal structure of SnO₂. No Er related impurity peaks could be observed. From the TEM micrographs average crystallite size was estimated to be 12 nm. The UV–visible absorption spectra of SnO₂:Er showed blue shift in the absorption shoulder compared with the spectra of undoped SnO₂ sample. Photoluminescence emission intensity of SnO₂:Er nanoparticles was found to be quenched with increasing concentration of Er³⁺ ions. The electron spin resonance (ESR) analysis of Er doped SnO₂ nanoparticles indicated Er in 3 + state with g = 2.     

Three-body interaction between an atom and a monolayer film

An atom (B) situated near a plane of atoms (A) experiences an interaction potential energy V = (V₂ + V₃ + … The leading term is the sum over the monlayer of 2-body interactions. We compute here the 3-body correction V₃. Numerical results are presented for the case of noble gases, H and CH₄. For H or He near a Xe layer, V₃ reduces the well depth by ~ 10%.     

Room-temperature ferromagnetism in pure and Mn doped SnO2 powders

We report here observation of ferromagnetism in pure and Mn doped SnO₂ powder with different Mn contents. Magnetic measurements revealed that all samples exhibit room temperature ferromagnetism (RTFM), which is identified as an intrinsic characteristic. The RTFM has been observed in the pure SnO₂ powder, which is believed to be defect induced, with a saturation magnetization of ～0.017 emu/g. The RTFM was enhanced considerably in the Mn doped samples and the magnetic properties strongly depend on doping content. A sample with 1% of Mn is ferromagnetic at room temperature with a saturation magnetization of ～0.98 emu/g, a remanent magnetization of ～27%, and a coercivity of ～270 Oe. The average magnetic moment per Mn atom decreases with increasing Mn content. Our results reveal that the large RTFM observed in Mn doped SnO₂ powder originates from a combination effect of oxygen vacancies and transition metal doping.     

Magnetism manipulation in ferromagnetic/ferroelectric heterostructures by electric field induced strain

Magnetization manipulation by an electric field(E-field) in ferromagnetic/ferroelectric heterostructures has attracted increasing attention because of the potential applications in novel magnetoelectric devices and spintronic devices, due to the ultra-low power consumption of the process. In this review, we summarize the recent progress in E-field controlled magnetism in ferromagnetic/ferroelectric heterostructures with an emphasis on strain-mediated converse magnetoelectric coupling. Firstly, we briefly review the history, the underlying theory of the magnetoelectric coupling mechanism, and the current status of research. Secondly, we illustrate the competitive energy relationship and volatile magnetization switching under an E-field. We then discuss E-field modified ferroelastic domain states and recent progress in non-volatile manipulation of magnetic properties. Finally, we present the pure E-field controlled 180° in-plane magnetization reversal and both E-field and current modified 180° perpendicular magnetization reversal.     

Two-dimensional atom localization induced by a squeezed vacuum

A scheme of two-dimensional(2D) atom localization induced by a squeezed vacuum is proposed, in which the threelevel V-type atoms interact with two classical standing-wave fields. It is found that when the environment is changed from an ordinary vacuum to a squeezed vacuum, the 2D atom localization is realized by detecting the position-dependent resonance fluorescence spectrum. For comparison, we demonstrate that the atom localization originating from the quantum interference effect is distinct from that induced by a squeezed vacuum. Furthermore, the combined effects of the squeezed vacuum and quantum interference are also discussed under appropriate conditions. The internal physical mechanism is analyzed in terms of dressed-state representation.