Magnetic metastability in tetrahedrally bonded magnetic III-nitride semiconductors

Results of density-functional calculations for isolated transition metal (TM = V, Cr, Mn, Fe, Co, Ni on cation sites) doped GaN demonstrate a novel magnetic metastability in dilute magnetic semiconductors. In addition to the expected high spin ground states (4muB/Mn and 5muB/Fe), there are also metastable low spin states (0muB/Mn and 1muB/Fe)--a phenomenon that can be explained in simple terms on the basis of the ligand field theory. The transition between the high spin and low spin states corresponds to an intraionic transfer of two electrons between the t2 and e orbitals, accompanied by a spin-flip process. The results suggest that TM-doped wideband semiconductors (such as GaN and AlN) may present a new type of light-induced spin-crossover material.     

TM掺杂的Ⅲ-Ⅴ族稀磁半导体电磁性质的第一原理计算

使用基于自旋局域密度泛函理论的第一性原理方法对3d过渡金属(TM=V，Cr，Mn，Fe，Co和Ni)掺杂的Ⅲ-Ⅴ族半导体(GaAs和GaP)的电磁性质进行了计算.结果发现：用V，Cr和Mn掺杂时体系将出现铁磁状态，而Fe掺杂时将出现反铁磁状态，Co和Ni掺杂时，其磁性则不稳定.其中，Cr掺杂的GaAs和GaP将可能是具有较高居里温度的稀磁半导体(DMS).在这些DMS系统中，V离子的磁矩大于理论期待值，Fe，Co和Ni离子的磁矩小于理论期待值，Cr和Mn离子的磁矩与期待值的差距取决于晶体的对称性以及磁性离子的能带分布.此外，使用Si和Mn共同对Ⅲ-Ⅴ族半导体进行掺杂，将有利于DMS表现为铁磁状态，并可以使体系的T_C进一步提高. 关键词： 稀磁半导体 过渡金属 掺杂 共掺杂     

过渡金属掺杂GaN的电子结构和光学性质理论研究

采用基于密度泛函理论的第一性原理平面波赝势法计算不同过渡金属（V, Cr, Mn, Fe, Co, Ni）掺杂GaN的电子结构及光学性质,分析掺杂对电子结构及光学性质的影响.结果表明,过渡金属掺杂在GaN的禁带中引入杂质能带,除掺Fe体系外其它掺杂体系都表现为半金属性.除掺Fe和Ni体系在低能区没有出现光吸收外,其它体系均在低能区杂质能级处出现光吸收.     

硫化锌纳米管稳定性、电子性质和磁性质的比较研究

用第一性原理方法系统地研究硫化锌纳米管的稳定性、电子性质和掺杂磁性质.比较三种纳米管的稳定性.研究表明,六边形截面的双壁管的稳定性最高,相同截面的单壁管稳定性次之,而圆截面的之字形和扶手椅纳米管稳定性最低.电子能带结构计算表明它们都是直接带隙半导体.纳米管表面氢吸附后,六边形截面的单壁管转变为间接带隙半导体.研究了磁性原子掺杂六边形截面管的磁性质.发现掺杂纳米管的形成能比纯纳米管的形成能低,说明掺杂过程是一个放热反应.纳米管的总磁矩等于掺杂的磁性原子的磁矩.这些单掺杂纳米管在可调磁的新材料方面有潜在的应用价值.     

过渡金属TM(V,Cr,Mn)掺杂ZnS的电子结构和磁性

采用基于密度泛函理论(DFT)的第一性原理赝势平面波方法,对过渡金属V、Cr、Mn 掺杂ZnS的超晶胞体系进行了几何结构优化,计算了晶格常数、电子结构与磁学性质。研究结果表明：掺入V,Cr后,ZnS表现出明显的半金属性,而掺入Mn后,半金属性不明显;掺入过渡金属TM(V,Cr,Mn)后系统产生的磁矩主要有杂质的3d态电子贡献,且磁矩的大小与过渡金属的电子排布有关。     

Mg12O12纳米线掺杂3过渡金属元素的第一性原理计算研究

基于密度泛函第一性原理计算,系统研究了Mg12O12笼状团簇组装一维纳米线及其掺杂3d族元素体系的几何结构与电子结构。结果表明：Mg12O12团簇组装一维纳米线为非磁性半导体,带隙值为3.16 eV;掺杂Sc和V后,体系由半导体转变为金属;掺杂Ti、Cr、Mn、Fe、Co、Ni、Cu后体系仍然保持半导体特性、但带隙值明显减小,而掺杂Zn时带隙值变化不大;掺杂V、Cr、Mn、Fe、Co、Ni、Cu后纳米线具有磁性。     

Local electronic structure and magnetic properties of 3d transition metal doped GaAs

The local electronic structure and magnetic properties of GaAs doped with 3d transition metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) were studied by using discrete variational method (DVM) based on density functional theory. The calculated result indicated that the magnetic moment of transition metal increases first and then decreases, and reaches the maximum value when Mn is doped into GaAs. In the case of Mn concentration of 1.4%, the magnetic moment of Mn is in good agreement with the experimental result. The coupling between impure atoms in the system with two impure atoms was found to have obvious variation. For different transition metal, the coupling between the impure atom and the nearest neighbor As also has different variation. Supported by the National Natural Science Foundation of China (Grant No. 10347010)     

Transition metal encapsulated hydrogenated silicon nanotubes: Silicon-based half-metal

One-dimensional hydrogenated silicon nanotubes (H-SiNTs) with transition metal atom encapsulated were systematically studied by using density functional theory. The band structures and magnetic properties of the H-SiNTs can be tailored by doping transition metal (TM) (TM = Cr, Mn, Fe, Co) atoms within the tube. The hydrogenated silicon nanotubes are semiconductors with wide band gaps. TM doping turns H-SiNTs to be metals or semiconductors with a very small gap, and TM atoms at the center of the tubes keep large magnetic moments. Robust half-metallicity is observed in Mn-doped H-SiNTs and it is free from Peierls distortion. Thus, H-SiNTs with encapsulated magnetic elements may find important applications in spintronic devices.     

3d过渡金属元素掺杂Al12N12纳米线几何结构和电子性能的第一性原理研究

基于密度泛函理论的第一性原理计算方法,系统地研究了不同3d过渡金属元素(Sc、Ti、V、Cr、Mn、Fe、Co和Ni)掺杂Al₁₂N₁₂纳米线的几何结构、稳定性和电子结构.结果表明：所有掺杂体系均是热力学稳定的;掺杂Ni时体系保留了原有的非磁性间接带隙半导体特性;当掺杂其它原子(Sc、Ti、V、Cr、Mn、Fe、Co)时体系仍然保持为半导体,但带隙明显减小.掺杂过渡金属原子对于Al₁₂N₁₂纳米线的电子结构具有明显的调控作用,在能带调控和光电方面有潜在的应用前景.     

Half-metallic diluted antiferromagnetic semiconductors

The possibility of half-metallic antiferromagnetism, a special case of ferrimagnetism with a compensated magnetization, in the diluted magnetic semiconductors is highlighted on the basis of the first-principles electronic structure calculation. As typical examples, the electrical and magnetic properties of II-VI compound semiconductors doped with 3d transition metal ion pairs--(V, Co) and (Fe, Cr)--are discussed.     

Chiral structures and tunable magnetic moments in 3d transition metal doped Pt₆ clusters

The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt 6 (M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt 7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps suggest that the doped clusters can have higher chemical activities than the pure Pt 7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt 6 clusters is from 0 μ B to 7 μ B , revealing that the MPt 6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties.     

过渡金属原子掺杂的锯齿型磷烯纳米带的磁电子学特性

利用基于密度泛函理论的第一性原理方法,研究了掺杂铁、钴和镍原子的锯齿型磷烯纳米带(ZPNR)的磁电子学特性.研究表明,掺杂和未掺杂ZPNR的结构都是稳定的.当处于非磁态时,未掺杂和掺杂钴原子的ZPNR为半导体,而掺杂铁或者镍原子的ZPNR为金属.自旋极化计算表明,未掺杂和掺杂钴原子的ZPNR无磁性,而掺杂铁或者镍原子的ZPNR有磁性,但只能表现出铁磁性.处于铁磁态时,掺杂铁原子的ZPNR为磁性半导体,而掺杂镍原子的ZPNR为磁性半金属.掺杂铁或者镍原子的ZPNR的磁性主要由杂质原子贡献,产生磁性的原因则是在ZPNR中存在未配对电子.掺杂位置对ZPNR的磁电子学特性有一定的影响.该研究对于发展基于磷烯纳米带的纳米电子器件具有重要意义.     

Computationally predicting spin semiconductors and half metals from doped phosphorene monolayers

First-principles computations are performed to investigate phosphorene monolayers doped with 30 metal and nonmetal atoms. The binding energies indicate the stability of all doped configurations. Interestingly, the magnetic atom Co doping induces the absence of the magnetism while the magnetism is realized in phosphorene with substitutional doping of nonmagnetic atoms (O, S, Se, Si, Br, and Cl). The magnetic moment of transition metal (TM)-doped systems is suppressed in the range of 1.0-3.97 μ_B. The electronic properties of the doped systems are modulated differently; O, S, Se, Ni, and Ti doped systems become spin semiconductors, while V doping makes the system a half metal. These results demonstrate potential applications of functionalized phosphorene with external atoms, in particular to spintronics and dilute magnetic semiconductors.     

Modulation of magnetic properties of bilayer SnSe with transition-metals doping in the interlayer

We investigate the spin-polarized electronic and magnetic properties of bilayer SnSe with transition-metal (TM) atoms doped in the interlayer by using a first-principles method. It shows that Ni dopant cannot induce the magnetism in the doped SnSe sheet, while the ground state of V, Cr, Mn, Fe and Co doped systems are magnetic and the magnetic moment mainly originates from 3d TM atom. Two types of factors, which reduce the magnetic moment of TM atoms doped in bilayer SnSe, are identified as spin-up channel of the 3d orbital loses electrons to SnSe sheet and spin-down channel of the 3d orbital gains electrons from 4s orbital. The spin polarization is found to be 100% at Fermi level for the Mn and Co atoms doped system, while the Ni-doped system is still a semiconductor with a gap of 0.26 eV. These results are potentially useful for development of spintronic devices.     

The magnetoelectric properties of A- or B-site-doped PbVO3 films： A first-principles study

We employ first-principles calculations to study the magnetic and ferroelectric properties of PbVO3 with A （XA = Ca, Sr, Bi, Ba, and La） or B （XB = Ti, Cr, Mn, Fe, Co, Ni, and Cu） site dopants, with the aim of ascertaining a large ferroelectric polarization and a long magnetic order, or even a macro fen＇i/ferromagnetism, which is critical to their potential applications in magnetoelectronic devices. It is found that PbTXAVsO24 （XA =Ca, Sr, and Ba,） are inclined to maintain the spin glass and large ferroelectric polarization. The degenerated G- and C-antiferromagnetic （AFM） couplings in the ideal PbVO3 are broken up, accompanied by the loss of ferroelectric properties, when La or Bi is doped at the A site. In contrast, the above-mentioned 3d transition elements doped at the B site of PbVO3 could induce remnant magnetic moments and preserve the large ferroelectric polarization, except for Ni and Cu. The Fe or Cr at the B site clearly remove the degenerated G- and C-AFM coupling, but the nonmagnetic Ti cannot do so. For the Mn, Co, Ni, or Cu doped at the B sites, even the two-dimensional AFM ordering in PbVO3 is destabilized. The various doping effects are further discussed with inner strain and charge transfer.     

Enhanced oscillator strengths and optical parameters of doped ZnS bulk and nanophosphors

We synthesize and investigate the oscillator-strength (OS), dipole-moment (DM), and integrated cross-section values (ICSVs) of singly (Mn) and doubly (Mn and Co or Ni) doped samples of ZnS bulk and nanophosphors. The oscillator-strength values (OSVs) are found to enhance by three orders of magnitude when Co or Ni dopant is incorporated in ZnS:Mn bulk phosphors, which strongly suggests that a quencher dopant triggered an energy-transfer process in the host ZnS material. Nevertheless, although these quencher dopants were previously considered to kill the luminescence from the host material, we used these dopants in ZnS:Mn to create an additional pathway for the relaxation of the carrier, and to initiate the energy-transfer mechanism. On the other hand, a four orders of magnitude enhancement in the OSVs was observed on incorporating the quencher dopants in ZnS:Mn nanophosphors, which is attributed to the fact that our nanosamples are related to a strong-confinement case while the quencher dopant played a significant role in the variation of OSVs. Moreover, the analysis of OSVs showed that excitonic/defect level emission from ZnS host is due to a weak electric dipole transition (WEDT), while a magnetic dipole transition (MDT) dominates in the case of ZnS:Mn nanophosphors. Based on the present investigations, we clearly obtained an origin of excitonic- and impurity-related emission from the doped ZnS bulk and nanophosphor samples, which were almost vague in the previous studies of other researchers.     

不同3d过渡金属掺杂对ZnS电子结构和光学性质的影响

采用基于密度泛函理论的第一性原理方法对掺杂不同3d过渡金属元素的闪锌矿型ZnS系统进行了研究。结果表明,掺杂元素的主要贡献在费米面附近,掺杂后系统的价带底、导带均向低能方向移动,带隙变小。Fe、Mn、Cr、V的掺杂为n型掺杂,Cu、Ni、Co的掺杂为p型掺杂。掺杂后系统的光学吸收边都有明显的红移,在绿光区有较强的吸收。此外,V和Cr掺杂系统在远紫外区也有较强的吸收,结果与实验符合。     

First-principles study on the magnetism and electronic structure in 3d transition metal (X=Sc,V, Cr,Mn, Fe,Ni, Cu) doped CoO

We have studied the electronic structure and magnetism of the single transitional metal element X=Sc, V, Cr, Mn, Fe, Ni, Cu-doped CoO systems by first-principles calculations. At X=Sc, Cr, Cu, the binding energy of the doped systems is lower than pure CoO, suggesting that these systems are energetically stable. In the Sc, V, Cr, Mn, Fe, Ni, Cu-doped 2×2×2 CoO supercells, the total magnetic moments are 3.03, 5.64, 6.80, 7.70, 6.93, 2.30 and 1.96 μ_B, respectively. At X=Cr and Fe, the doped CoO systems are half-metallic with a high spin polarization. The large magnetic moment and high spin polarization in the Cr and Fe-doped CoO are important for the design of the spintronic devices.     

Chiral structures and tunable magnetic moments in 3d transition metal doped Pt6 clusters

The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt6 （M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn） are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital （HOMO） lowest unoccupied molecular orbital （LUMO） gaps suggest that the doped clusters can have higher chemical activities than the pure Pt7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt6 clusters is from 0 μB to 7 μB, revealing that the MPt6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties.     

3d过渡金属掺杂对Cd12O12纳米线电子和磁性能的影响

采用基于密度泛函理论的第一性原理计算方法,系统研究了3d过渡金属元素(Sc、Ti、Cr、Mn、Co、Cu和Zn)掺杂Cd12O12纳米线的几何结构,电子结构和磁性。结果表明：所有掺杂体系均是热力学稳定的;掺杂Ti或Zn时体系保留了原有的非磁半导体特性,掺杂Mn、Co或Cu时能够实现磁性半导体态,而在掺杂Sc（Cr）时体系转变为非磁性金属态（磁性金属态）。研究结果表明,掺杂3d过渡金属元素的Cd12O12纳米线在电子、光电和自旋电子学领域具有潜在的应用价值。