Structural,electronic, and magnetic properties of 3d transition metal doped GaN nanosheet: A first‐principles study

We have performed the first‐principles calculations on the structural, electronic, and magnetic properties of 3d transition‐metal? (Cr, Mn, Fe, Co, and Ni) atoms doped 2D GaN nanosheet. The results show that 3d TM atom substituting one Ga leads to a structural reconstruction around the 3d TM impurity compared to the pristine GaN nanosheet. The doping of TM atom can induce magnetic moments, which are mainly located on the 3d TM atom and its nearest‐neighbor N atoms. It is found that Mn‐ and Ni‐doped GaN nanosheet with 100% spin polarization characters seem to be good candidates for spintronic applications. When two Ga atoms are substituted by two TM dopants, the ferromagnetic (FM) ordering becomes energetically more favorable for Cr‐, Mn‐, and Ni‐doped GaN nanosheet with different distances of two TM atoms. On the contrary, the antiferromagnetic (AFM) ordering is energetically more favorable for Fe‐doped GaN nanosheet. In addition, our GGA + U calculations show the similar results with GGA calculations. © 2016 Wiley Periodicals, Inc.     

Structural, electronic, and magnetic properties of Con(benzene)m complexes

The structural, electronic, and magnetic properties of cobalt-benzene complexes (Co(n)Bz(m), n, m = 1-4, m = n, n + 1) have been explored within the framework of an all electron gradient-corrected density functional theory. Sandwich conformations are energetically preferred for the smallest series of n, m = 1-2, rice-ball structures are for larger sizes with n > or = 3, and both motifs coexist for Co(2)Bz(3). The rice-ball clusters of (3, 3) and (4, 4) are more stable than (3, 4) having a relative large binding energy and HOMO-LUMO gap whereas smaller sandwich clusters have highly kinetic stability at (n, n + 1). The computed ionization potentials and magnetic moments of Co(n)Bz(m) are in good agreement with the measured values overall; the present results suggest that the measured moments are averages reflecting mixtures of a few nearly isoenergetic isomers having different spin states. The magnetism of the complexes mainly comes from Co atoms with a Bz molecule only possessing very small moments. Ferromagnetic ordering is energetically preferred for smaller complexes with n = 1-3 whereas antiferromagnetic ordering is favored for (4, 4). The relatively smaller moments of Con clusters in a Bz matrix indicate that Bz molecules play an attenuation role to the magnetism of the complexes.     

First principles study of the stability and electronic structure of the icosahedral La13, La(-1) (13), and La(+1) (13) clusters

The structural stability and electronic-structure of icosahedral La(13), La(-1) (13), and La(+1) (13) clusters have been studied by DMOL cluster method based on density-functional theory. The ground state of all-electron with relativity results is shown to be a distorted D(2h) icosahedron by the Jahn-Teller effect. However, the binding energies of D(3d) and D(5d) are very close to that of the D(2h) structure for La(13), La(-1) (13), and La(+1) (13) clusters. The effective core potential results show that the true ground state is D(5d) structure. The clusters have small magnetic moments and the symmetry of cluster is an important factor in determining the magnetic moments of the clusters. The effects of interatomic spacing and coordination on atomic magnetic moment are discussed. Further, 5d electrons dominate the hybrid orbitals below the Fermi level in the neutral cluster and contribute the main spin of clusters.     

Competing magnetic interactions in Na10Co4O10, studied by neutron diffraction

Na(10)Co(4)O(10) was investigated by neutron powder diffraction at 230, 70, and 4 K. The crystal structure, determined previously by X-ray diffraction on single crystals, was confirmed. Na(10)Co(4)O(10) orders magnetically below 37 K. All observed magnetic reflections could be indexed by integers (hkl) with respect to the chemical unit cell and the magnetic propagation vector q=0. The refinement was performed in the Shubnikov space group C2/c and indicated a collinear antiferromagnetic spin structure. The determined spin arrangement is consistent with the magnetic intratetramer interactions suggested previously from the analysis of magnetic susceptibility data: the magnetic moments of the central Co(III) ions of the Co(4)O(10) tetramer lie parallel to each other and couple in an antiparallel fashion to the terminal Co(II) moments. The Rietveld analysis shows that the net moments of 0.64 mu(B) per tetramer form ferromagnetic layers parallel to the ab plane. Adjacent layers are coupled antiferromagnetically along c. The spins are aligned in the ac plane along the line connecting adjacent Co(II) and Co(III) ions of the tetramer. We have determined unusually low values for the ordered magnetic moments of 2.43(5) mu(B) and 2.11(6) mu(B) for Co(III) and Co(II), respectively. The occurrence of spontaneous magnetization below 37 K indicates a slight canting of 2.2 degrees of the antiferromagnetic structure. A representation analysis shows that a weak ferromagnetic component along b is compatible with the determined antiferromagnetic structure.     

A theoretical study on small iridium clusters: structural evolution, electronic and magnetic properties, and reactivity predictors

The structural, electronic, and magnetic properties of iridium clusters with sizes of n = 2-15 are investigated by employing the generalized gradient approximation of density functional theory. Simple cube evolution pattern is revealed for Ir(2-15) clusters, as predicted by previous reports. It is remarkable that for Ir(10), Ir(11) clusters, new generated isomers with higher stabilities relative to those reported in previous studies are obtained. The even-sized clusters are more stable than the odd-sized species. The Ir-Ir bonds in the cubic Ir(8) and Ir(12) clusters, which are considered as the basic units in the structural evolution present covalent character. Starting from n = 8, the magnetic moments of Ir(n) clusters decrease sharply. The moments of magnetic clusters show 5d characters. The reactive site selectivity of studied clusters with n = 5-15 is analyzed with condensed Fukui function. The capped atoms in certain clusters (Ir(9), Ir(10), Ir(11), and Ir(13)) generally show extraordinary activity for both nucleophilic and electrophilic attack.     

A tale of two metals: new cerium iron borocarbide intermetallics grown from rare-earth/transition metal eutectic fluxes

R(33)Fe(14-x)Al(x+y)B(25-y)C(34) (R = La or Ce; x ≤ 0.9; y ≤ 0.2) and R(33)Fe(13-x)Al(x)B(18)C(34) (R = Ce or Pr; x < 0.1) were synthesized from reactions of iron with boron, carbon, and aluminum in R-T eutectic fluxes (T = Fe, Co, or Ni). These phases crystallize in the cubic space group Im3m (a = 14.617(1) ?, Z = 2, R(1) = 0.0155 for Ce(33)Fe(13.1)Al(1.1)B(24.8)C(34), and a = 14.246(8) ?, Z = 2, R(1) = 0.0142 for Ce(33)Fe(13)B(18)C(34)). Their structures can be described as body-centered cubic arrays of large Fe(13) or Fe(14) clusters which are capped by borocarbide chains and surrounded by rare earth cations. The magnetic behavior of the cerium-containing analogs is complicated by the possibility of two valence states for cerium and possible presence of magnetic moments on the iron sites. Temperature-dependent magnetic susceptibility measurements and M?ssbauer data show that the boron-centered Fe(14) clusters in Ce(33)Fe(14-x)Al(x+y)B(25-y)C(34) are not magnetic. X-ray photoelectron spectroscopy data indicate that the cerium is trivalent at room temperature, but the temperature dependence of the resistivity and the magnetic susceptibility data suggest Ce(3+/4+) valence fluctuation beginning at 120 K. Bond length analysis and XPS studies of Ce(33)Fe(13)B(18)C(34) indicate the cerium in this phase is tetravalent, and the observed magnetic ordering at T(C) = 180 K is due to magnetic moments on the Fe(13) clusters.     

Transition-metal 13-atom clusters assessed with solid and surface-biased functionals

First-principles density-functional theory studies have reported open structures based on the formation of double simple-cubic (DSC) arrangements for Ru(13), Rh(13), Os(13), and Ir(13), which can be considered an unexpected result as those elements crystallize in compact bulk structures such as the face-centered cubic and hexagonal close-packed lattices. In this work, we investigated with the projected augmented wave method the dependence of the lowest-energy structure on the local and semilocal exchange-correlation (xc) energy functionals employed in density-functional theory. We found that the local-density approximation (LDA) and generalized-gradient formulations with different treatment of the electronic inhomogeneities (PBE, PBEsol, and AM05) confirm the DSC configuration as the lowest-energy structure for the studied TM(13) clusters. A good agreement in the relative total energies are obtained even for structures with small energy differences, e.g., 0.10 eV. The employed xc functionals yield the same total magnetic moment for a given structure, i.e., the differences in the bond lengths do not affect the moments, which can be attributed to the atomic character of those clusters. Thus, at least for those systems, the differences among the LDA, PBE, PBEsol, and AM05 functionals are not large enough to yield qualitatively different results.     

Joint photoelectron and theoretical study of (Rh(m)Co(n))⁻ (m=1-5, n=1-2) cluster anions and their neutral counterparts

Anion photoelectron spectroscopic experiments and calculations based on density functional theory have been used to investigate and uniquely identify the structural, electronic, and magnetic properties of both neutral and anionic (Rh(m)Co(n)) and (Rh(m)Co(n))(-) (m=1-5, n=1-2) clusters, respectively. Negative ion photoelectron spectra are presented for electron binding energies up to 3.493 eV. The calculated electron affinities and vertical detachment energies are in good agreement with the measured values. Computational results for geometric structures and magnetic moments of both cluster anions and their neutrals are presented.     

Structure, bonding, and magnetism in manganese clusters

We investigate the structures and magnetic properties of small Mn(n) clusters in the size range of 2-13 atoms using first-principles density functional theory. We arrive at the lowest energy structures for clusters in this size range by simultaneously optimizing the cluster geometries, total spins, and relative orientations of individual atomic moments. The results for the net magnetic moments for the optimal clusters are in good agreement with experiment. The magnetic behavior of Mn(n) clusters in the size range studied in this work ranges from ferromagnetic ordering (large net cluster moment) for the smallest (n=2, 3, and 4) clusters to a near degeneracy between ferromagnetic and antiferromagnetic solutions in the vicinity of n=5 and 6 to a clear preference for antiferromagnetic (small net cluster moment) ordering at n=7 and beyond. We study the details of this evolution and present a picture in which bonding in these clusters predominantly occurs due to a transfer of electrons from antibonding 4s levels to minority 3d levels.     

A unique 2D framework containing linear trimeric cobalt(II) of mixed Td-Oh-Td geometries linked by two different single-carboxylate-aromatic amine ligands: structure and magnetic properties

A new 2D coordination polymer Co3(OH)2(pa)2(ina)2 (1, pa = 3-(1H-benzimidazol-2-yl) propanoic carboxylate, ina = isonicotinate) contained uncommon, linear Co(ii) trimers of mixed Td-Oh-Td geometries, exhibits spin canting below 20 K. Such magnetic behavior mainly arises from the Dzyaloshinski-Moriya interaction from the anisotropic, mixed geometries trimeric Co(II) ions to the crimpled 2D network based on the nature of the binding modes of Co(II)-carboxylate trimer and the effect of the intertrimers arrangement of 1. The mixed single-carboxylate-aromatic amine ligands bridged metal systems display a new structurally authenticated example of a thick 2D layer, and also indicate homometallic Co(II) clusters with Td-Oh-Td mixed-geometries can result in relatively obvious noncompensation moments, according to different efficient spins of Co(II) at very low temperature, in spite of antiferromagnetic intracluster interactions.     

Structures,magnetic properties,and electronic counting rule of metals‐encapsulated cage‐like M2 Si18 (M = Ti‐Zn) clusters

The geometries, magnetic properties and stabilities of the transition metal (TM) atoms encapsulated M₂Si₁₈ (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) clusters have been systematically calculated by using the density function theory with generalized gradient approximation. Only when the doping metal atom has no more than half‐full d electronic shell, a double hexagonal prism cage‐like M₂Si₁₈ structure could form. The total moments of M₂Si₁₈ are either 0 or 2μ_B. Co₂Si₁₈ is the most stable cluster among all 3d doped M₂Si₁₈ clusters. The model of shell closure at the TM atom may be helpful to understand the stability of M₂Si₁₈ clusters. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Electronic and magnetic properties of all 3d transition‐metal‐doped ZnO monolayers

Stable geometries, electronic structures, and magnetic properties of the ZnO monolayer doped with 3d transition‐metal (TM) (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) atoms substituting the cation Zn have been investigated using first‐principles pseudopotential plane wave method within density functional theory (DFT). It is found that these nine atomic species can be effectively doped in the ZnO monolayer with formation energies ranging from ?6.319 to ?0.132 eV. Furthermore, electronic structures and magnetic properties of ZnO monolayer can be modified by such doping. The results show that the doping of Cr, Mn, Fe, Co, Ni, and Cu atoms can induce magnetization, while no magnetism is observed when Sc, Ti, and V atoms are doped into the ZnO monolayer. The magnetic moment is mainly due to the strong p–d mixing of O and TM (Cr, Mn, Fe, Co, Ni, and Cu) orbitals. These results are potentially useful for spintronic applications and the development of magnetic nanostructures. © 2013 Wiley Periodicals, Inc.     

Ge_nEu(n=1-13)团簇的结构、电子及磁性质(英文)

利用密度泛函理论在广义梯度近似下研究了GenEu(n=1-13)团簇的生长模式和磁性.结果表明:对于GenEu(n=1-13)团簇的基态结构而言,没有Eu原子陷入笼中.这和SinEu以及其它过渡金属掺杂半导体团簇的生长模式不同.除GeEu团簇外,GenEu(n=2-13)团簇的磁矩均为7μB.团簇的总磁矩与Eu原子的4f轨道磁矩基本相等.Ge、Eu原子间的电荷转移以及Eu原子的5d、6p和6s间的轨道杂化可以增强Eu原子的局域磁矩,却不能增强团簇总磁矩.     

Stability, structural, and magnetic phase diagrams of ternary ferromagnetic 3d-transition-metal clusters with five and six atoms

We report a theoretical investigation of free-standing Fe(x)Co(y)Ni(z) ternary clusters with x + y + z = 5 and 6. Our study is performed within density functional theory as implemented in the GAUSSIAN 03 set of programs and with the BPW91/SDD level of theory. We analyze the geometries, chemical order, local and total magnetic moments, binding energies, excess energies, and second difference in the energy in the whole range of composition, from which structural, magnetic, and stability phase diagrams are predicted for these cluster sizes. We determine the optimal stoichiometries for these clusters as regards the maximum total magnetic moment and stability.     

Con(n=2～10)团簇的结构和磁性

采用密度泛函理论中的局域自旋密度近似(LSDA)和广义梯度近似(GGA)对Con(n=2～10)团簇的几何构型进行优化，并对能量、频率和磁性进行了计算,两种方法确定的基态构型完全一致,并从平均键长、平均配位数和对称性对磁性的影响进行了理论探讨.研究表明, Con(n=2～10)基态团簇的磁性在n=2～4时主要受平均键长的影响,在n=5～9时主要受平均配位数的影响,在n=10时受原子间距和平均配位数的相互影响,最终导致与Co8基态团簇具有相同的磁性.基态团簇在Co5和Co9出现了磁性局域最小点.     

No quenching of magnetic moment for the GenCo (n=1-13) clusters: first-principles calculations

The authors predict that for the Ge(n)Co (n=1-13) clusters the magnetic moment does not quench, which is dark contrast to the previous results with transition-metal-doped Si(n) clusters. It may be due to the unpaired electrons of the Co atom in the clusters. For the ground state structures of the Ge(n)Co (n>or=9) clusters, the Co atom completely falls into the center of the Ge outer frame, forming metal-encapsulated Ge(n) cages. The doping of the Co atom enhances the stability of the host Ge(n) clusters. The Ge(10)Co cluster with the bicapped tetragonal antiprism structure is more stable than others, which agrees very well with the results of the experiment of the Co/Ge binary clusters by the laser vaporization.     

Effect of hydrogen chemisorption on the magnetism of nickel clusters

Results of self-consistent field, local spin density, scattered wave calculations are reported for nickel clusters of 10, 13, and 14 atoms and these clusters interacting with one or two chemisorbed hydrogen atoms. The pure nickel clusters all have a reasonable average atomic magnetic moment (the average over all the clusters is 0.66µ_B) and the addition of hydrogen reduces this moment in each case. The reduction of magnetic moment is clearly larger on the nickel atoms that are nearest to hydrogen but there is also a noticeable change in the moments of the other atoms of the clusters. Three factors, of varying importance for the different clusters, contribute to the changes in the overall and local magnetic moments: (i) The extra electron brought in with the hydrogen goes into a down-spin Ni d level, reducing the moment. (ii) The reelectron duced moment is accompained by a reduced exchange splitting and consequently some up-spin d electrons, not directly involved in the bonding to hydrogen, are transferred to lower lying down-spin d orbitals. (iii) For atoms close to the adsorbate, d character in the local density of states is pushed above the Fermi level through antibonding interactions with the hydrogen, further reducing the moments of these atoms.     

FMBen（FM=Fe,Co,Ni;n=1-12）团簇结构和电子性质

采用密度泛函理论中的广义梯度近似对FMBen(FM=Fe,Co,Ni;n=1-12)团簇的几何构型进行优化,并对能量、频率和磁性进行了计算,同时考虑了电子的自旋多重度.结果表明,纯铍团簇的幻数是由电子的壳层模型确定,而FMBen团簇的幻数主要由几何效应来解释;掺杂铁磁性的过渡金属(Fe,Co,Ni)提高了纯团簇的稳定性.二阶能量差分表明FMBen(FM=Fe,Co,Ni)的幻数分别为5,10;5,10;4,10.通过对磁性质的研究发现掺杂不同的过渡金属时,磁矩出现了不同的变化规律.     

FMBen(FM=Fe,Co, Ni; n=1-12)团簇结构和电子性质

采用密度泛函理论中的广义梯度近似对FMBen(FM=Fe, Co, Ni; n=1-12)团簇的几何构型进行优化, 并对能量、频率和磁性进行了计算, 同时考虑了电子的自旋多重度. 结果表明, 纯铍团簇的幻数是由电子的壳层模型确定, 而FMBen团簇的幻数主要由几何效应来解释; 掺杂铁磁性的过渡金属(Fe, Co, Ni)提高了纯团簇的稳定性. 二阶能量差分表明FMBen(FM=Fe, Co, Ni)的幻数分别为5, 10; 5, 10; 4, 10. 通过对磁性质的研究发现掺杂不同的过渡金属时, 磁矩出现了不同的变化规律.