C、N、O掺杂CuBr和CuCl的电子结构和磁性的第一性原理研究

本文基于密度泛函理论(DFT)结合广义梯度近似(GGA),采用第一性原理的平面波赝势方法,探究非磁性sp元素(C、N和O)掺杂卤化物(Cu Cl和Cu Br)是否能诱导产生半金属铁磁性.通过计算体系总能量、能带、态密度和分态密度,分析了非磁性元素掺杂卤化物体系的电子结构和磁性;通过对材料加压,给出了体系铁磁性随压强变化的趋势并作了分析.最后计算显示,O和N掺杂能诱导Cu Cl产生稳定的半金属铁磁性,随着压强的增大Cu Cl0.75N0.25和Cu Cl0.75O0.25的铁磁性减弱最终发生磁相变由铁磁态(FM)转变为非铁磁态(NM).     

Magnetic properties of AlN monolayer doped with group 1A or 2A nonmagnetic element: First-principles study

The electronic structure, magnetic properties, and mechanism of magnetization in two-dimensional(2D) aluminum nitride(AlN) monolayer doped with nonmagnetic elements of group 1A(Li, Na, K) or group 2A(Be, Mg, Ca) were systematically investigated using first-principles studies. Numerical results reveal that the total magnetic moments produced by group 1A and group 2A nonmagnetic doping are 2.0μB and 1.0μB per supercell, respectively. The local magnetic moments of the three N atoms around the doping atom are the primary moment contributors for all these doped AlN monolayers. The p orbital of the dopant atom contributes little to the total magnetic moment, but it influences adjacent atoms significantly, changing their density of states distribution, which results in hybridization among the p orbitals of the three closest N atoms, giving rise to magnetism. Moreover, the doped AlN monolayer, having half-metal characteristics,is a likely candidate for spintronic applications. When two group 1A or group 2A atoms are inserted, their moments are long-range ferromagnetically coupled. Remarkably, the energy of formation shows that, if the monolayer has been grown under N-rich conditions, substitution of a group 2A atom at an Al site is easier than substitution of a group 1A atom.     

Magnetic characteristics of Au–Mn nanowires

The quantum properties of Au–Mn nanowires are analyzed theoretically from first principles. The emergence of magnetic properties in these nanowires, consisting of nonmagnetic elements, is demonstrated. It is shown that the manganese atoms carry fairly large magnetic moments (～4.3 μ_B), although crystalline Mn is a paramagnet. Analysis of the electronic structure of these bimetallic nanowires indicates that the magnetic moments at the Mn atoms arise owing to the formation of a complicated structure of hybrid orbitals. Furthermore, it is found that the antiferromagnetic state in Au–Mn nanowires is stabilized by the occurrence of indirect exchange interaction between Mn atoms.     

Ab initio study on magnetism at GaN (100) and (101) surfaces

The magnetism of GaN (100) and (101) surfaces containing neutral intrinsic defects has been investigated using ab inito calculations. Ideal Ga-ended GaN (100) surfaces and (101) surfaces are nonmagnetic. After surface relaxation, an N-ended GaN (100) surface transforms to a Ga-end, which presents local magnetic moments being ferromagnetically coupled. Neutral gallium vacancies at the (100) surface bring about large magnetic moments, which are ferromagnetically coupled. The spin-polarization of 2p electrons of nitrogen atoms is responsible for the induced magnetic moments. Neutral nitrogen vacancies at the (101) surface induce a zero magnetic moment. Neutral gallium vacancies at the (101) surface might lead to an antiferromagnetic state.     

Magnetizing oxides by substituting nitrogen for oxygen

We describe a possible pathway to new magnetic materials with no conventional magnetic elements present. The substitution of nitrogen for oxygen in simple nonmagnetic oxides leads to holes in N 2p states which form local magnetic moments. Because of the very large Hund's rule coupling of Nitrogen and O 2p electrons and the rather extended spatial extent of the wave functions these materials are predicted to be ferromagnetic metals or small band gap insulators. Experimental studies support the theoretical calculations with regard to the basic electronic structure and the formation of local magnetic moments. It remains to be seen if these materials are magnetically ordered and, if so, below what temperature.     

Magnetism in transition-metal-doped silicon nanotubes

Using first-principles density functional calculations, we show that hexagonal metallic silicon nanotubes can be stabilized by doping with 3d transition metal atoms. Finite nanotubes doped with Fe and Mn have high local magnetic moments, whereas Co-doped nanotubes have low values and Ni-doped nanotubes are mostly nonmagnetic. The infinite Si24Fe4 nanotube is found to be ferromagnetic with nearly the same local magnetic moment on each Fe atom as in bulk iron. Mn-doped nanotubes are antiferromagnetic, but a ferrromagnetic state lies only 0.03 eV higher in energy with a gap in the majority spin bands near the Fermi energy. These materials are interesting for silicon-based spintronic devices and other nanoscale magnetic applications.     

Ferromagnetism in Rh-doped SnO<Subscript>2</Subscript> from first-principles calculation

The electronic structures and magnetic properties for Rh-doped SnO₂ crystals have been investigated by density functional theory. The results demonstrate a magnetic moment, which mainly arises from d orbital of Rhodium, of 1.0 μ _B per Rhodium with a little contribution from the Oxygen atoms surrounding it. The Rh-doped SnO₂ system exhibits half-metallic ferromagnetism with high Curie temperature. Several doped configurations calculations show that there are some robust ferromagnetic couplings between these local magnetic moments. The p–d hybridization mechanism is responsible for the predicted ferromagnetism. These results suggest a recipe obtaining promising dilute magnetic semiconductor by doping nonmagnetic elements in SnO₂ matrix.     

Ferromagnetism induced by intrinsic defects and nitrogen substitution in SnO2 nanotube

The possibilities of magnetism induced by intrinsic defects and nitrogen substitution in (5,5) single-wall SnO₂ nanotube are investigated by ab initio calculations. The calculated results indicate that a stoichiometric SnO₂ nanotube is nonmagnetic. The tin (Sn) vacancy can induce the magnetic moments rather than oxygen vacancy, which is originated from the polarization of O 2p electrons. A couple of tin vacancies can lead to the ferromagnetic coupling. A nitrogen substitution for oxygen also produces magnetic moments. When substituting two nitrogen atoms, the characteristics of exchange coupling depend upon the distance of two nitrogen atoms. The longer distance of two nitrogen atoms prefers the ferromagnetic coupling, whereas the short distance leads to the antiferromagnetic coupling.     

Electronic and magnetic properties of 3d transition-metal selenides from first principles

We have studied the electronic and magnetic properties of the PbO-type 3d transition-metal selenides (TMSes) by first principles calculations. We find that TiSe and VSe have ionic type bonds and the other TM-Se bonds are the mixed metallic-ionic-covalent type similar to the Fe–As bonds in the iron-based superconductors. FeSe has the shortest TM-Se bond and unique stripe antiferromagnetic ground state. CrSe and MnSe have a ferromagnetic ground state, while the other TMSes have a nonmagnetic ground state. Both nonmagnetic Co dopants and magnetic Mn dopants in FeSe compress the stripe antiferromagnetic state, while the magnetic trends are different as the doping concentration increases.     

A first-principles study of the magnetic properties in boron-doped ZnO

First-principles calculations based on density functional theory are performed to study the origin of ferromagnetism in boron-doped ZnO. It is found that boron atoms tend to reside at Zn sites. The induced Zn vacancy is a key factor for ferromagnetism in Zn1-xBxO (0相似文献   

Effects of enhanced electronic correlation on magnetic properties of light non-metallic element (B,C, N,and O)-doped CuCl: A first-principles study

Based on density functional calculations within both standard generalized gradient approximation and plus on-site Coulomb interactions approaches, we have investigated the electronic structure and magnetic properties of the first-row element-doped CuCl semiconductors. The electronic correlations in both 2p and 3d orbitals are enhanced by adding the on-site Coulomb repulsion (Hubbard U and Hund exchange J). After a comparative study, we find that, for both standard and beyond approaches, B-doped CuCl is a half-metallic magnet with majority-spin impurity bands touching the Fermi level, C-doped CuCl is a magnetic semiconductor, and N-doped CuCl is a half-metallic magnet with minority-spin impurity bands crossing the Fermi level. Nevertheless, for O-doped CuCl, it transforms from a nonmagnetic semiconductor to a half-metallic magnet with metallic up-spins by considering the correlation effects. The calculation shows that the enhanced electronic correlation not only corrects the error of band-gap, but also influences the magnetic ground state and the distribution of local magnetic moments. The location of impurity bands with different dopants was understood based on the elements' electronegativity and interaction between dopant and host atoms. Strong hybridization between the dopant's 2p states and the filled 3d orbitals of adjacent Cu yields the main contribution to magnetization.     

Ab initio study of electronic and magnetic properties in TM-doped 2D silicon carbide

The magnetic properties of SiC monolayer with different TM atoms and substitutional sites are investigated using first-principles method. Magnetism is observed for all the TM dopants. The magnetic moments and binding energies are quite different between Si (TM_Si) and C (TM_C) sites. Dependent to the larger magnetic moments and binding energy, we also investigate the interaction between two Mn atoms in the TM_Si system. The results show that the ferromagnetic states are originated by the p–d hybridization mechanism between Mn and its neighboring C atoms. Moreover, the antiferromagnetic coupling is observed with increasing Mn-Mn distance, which can be explained by two-impurity Haldane-Anderson model using quantum Monte Carlo method.     

First-principle study of magnetism in Co-doped SnO2

The effects of Co dopants and oxygen vacancies on the electronic structure and magnetic properties of the Co-doped SnO₂ are studied by the first-principle calculations in full-potential linearized augmented plane wave formalism within generalized gradient approximations. The Co atoms favorably substitute on neighboring sites of the metal sublattice. Without oxygen vacancies, the Co atoms are at low spin state independent of concentration and distribution of Co atoms, and only the magnetic coupling between nearest-neighbor Co atoms is ferromagnetic through direct exchange and super-exchange interaction. Oxygen vacancies tend to locate near the Co atoms. Their presence strongly increases the local magnetic moments of Co atoms, which depend sensitively on the concentration and distribution of Co atoms. Moreover, oxygen vacancies can induce the long-range ferromagnetic coupling between well-separated Co atoms through the spin-split impurity band exchange mechanism. Thus the room temperature ferromagnetism observed experimentally in the Co-doped SnO₂ may originate from the combination of short-range direct exchange and super-exchange interaction and the long-range spin-split impurity band exchange model.     

Localized magnetic states in graphene

We examine the conditions necessary for the presence of localized magnetic moments on adatoms with inner shell electrons in graphene. We show that the low density of states at the Dirac point, and the anomalous broadening of the adatom electronic level, lead to the formation of magnetic moments for arbitrarily small local charging energy. As a result, we obtain an anomalous scaling of the boundary separating magnetic and nonmagnetic states. We show that, unlike any other material, the formation of magnetic moments can be controlled by an electric field effect.     

Generalized mean-field theory for lattice magnetic systems and ferromagnetism of semiconductors with magnetic impurities

Mean-field theory is generalized to lattice systems of interacting magnetic moments by introducing a distribution function of random local magnetic fields to take into account the nonequivalence of various lattice sites. Analytical and numerical methods developed in this approach are used to describe ferromagnetism of nonmagnetic semiconductors with magnetic impurities.     

Role of Ga-doping in ironben gallium alloy clusters

The structural and magnetic properties of Fe_n-mGa_m (n=3～6, m=0～2; n=13, m=0～3) alloy clusters have been studied using density functional theory. The substitutional doping is favourable for small clusters with up to six atoms at low Ga concentration and substitutional Ga atoms in 13-atom clusters prefer surface sites. The Ga-doping generally could reduce the energetic stability but enhance the electronic stability of Fe clusters, along with a decrease of the local magnetic moments of Fe atoms around Ga dopants. These findings provide a microscopic insight into Fe-Ga alloys which are well-known magnetostriction materials.     

Electronic and magnetic properties of multishell Co nanowires coated with Cu

The structural, electronic, and magnetic properties of ultrathin Cu-coated Co nanowires have been studied by using empirical genetic algorithm simulations and a tight-binding spd model Hamiltonian in the unrestricted Hartree-Fock approximation. For some specific stoichiometric compositions, Cu atoms occupy the surface, while Co atoms prefer to stay in the interior, forming the perfect coated multishell structures. The outer Cu layers lead to substantial variations in the magnetic moment of interior Co atoms, depending on the structure and thickness of Cu layers. In particular, single Co atom row at the center of nanowire is found to be nonmagnetic when coated with two Cu layers. All the other Co nanowires in the coated Cu shell are still magnetic but the magnetic moments are reduced as compared with Co nanowires without Cu coating. The interaction between Cu and Co atoms induces nonzero magnetic moment for Cu atoms.     

First-principles calculations of 5d atoms doped hexagonal-AlN sheets：Geometry,magnetic property and the influence of symmetry and symmetry-breaking on the electronic structure

The geometry, electronic structure and magnetic property of the hexagonal AlN(h-AlN) sheet doped by 5d atoms(Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the density functional theory. The influence of symmetry and symmetry-breaking is also studied. There are two types of local symmetries of the doped systems: C3v and D3h. The symmetry will deviate from exact C3v and D3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0μBfor Lu, Ta and Ir; 1μB for Hf, W, Pt and Hg; 2μB for Re and Au; and 3μB for Os and Al-vacancy. The total densities of state are presented, where impurity energy levels exist. The impurity energy levels and total magnetic moments can be explained by the splitting of 5d orbitals or molecular orbitals under different symmetries.     

Ferromagnetism in phosphorus-doped ZnO: First-principles calculation

The electronic structure and magnetic properties of nonmagnetic phosphorus doped ZnO are investigated using first-principles calculation. Both generalized gradient approximation (GGA) and GGA + U calculations show that each substitutional P atom in ZnO induces a magnetic moment of about 1.0 μ_B, which come mainly from the partially filled p orbitals of the substitutional P and its 12 second neighboring O atoms. The magnetic coupling between the moments induced by P doping is ferromagnetic. The calculated electronic structures indicate that the ferromagnetic coupling can be explained in terms of the two band coupling model.     

Nd(Fe,Si)11Cx化合物的全电子计算(x=0,2)

采用基于第一原理的全势能线性缀加平面波加局域轨道((L)APW lo)方法对Nd(Fe,Si)11Cx化合物(x=0,2)的电子结构进行了计算,得到了化合物态密度和磁矩等信息.计算结果表明NdFe9Si2化合物中Si原子主要与4b和32i位Fe原子产生杂化,导致Fe原子磁矩减小.NdFe9Si2C2化合物C原子使32i位Fe原子磁矩进一步降低,同时减弱了Si原子的影响,使得4b位Fe原子磁矩增大.