(Ga,Mn)As 体系中Mn自补偿效应的第一性原理研究

基于密度泛函理论的赝势平面波方法计算了处于填隙位置磁性原子(MnI)对(Ga,Mn) As体系电子结构和磁性的影响. 计算结果表明MnI在GaAs中是施主；代替Ga位的MnGa 与MnI的自旋按反铁磁序排列；静电相互作用使MnGa，MnI倾向于形成MnGa_MnI对. MnI的存在一方面补偿了(Ga,Mn)As中的空穴，降低了空穴浓度；同时还使邻近的MnG a失活. MnI的存在对获得高居里温度的(Ga,Mn)As是极为不利的. 关键词： (Ga Mn)As 稀磁半导体 密度泛函理论     

室温下(Ga,Mn)As中载流子的自旋弛豫特性

运用飞秒时间分辨抽运-探测克尔光谱技术,研究了室温下退火及未退火(Ga,Mn)As的载流子自旋弛豫的激发能量密度依赖性,发现电子自旋弛豫时间随激发能量密度增加而增大,而在同一激发能量密度下,退火样品比未退火样品具有更短的载流子复合时间、电子自旋弛豫时间和更大的克尔转角,显示DP机理是室温下(Ga,Mn)As的电子自旋弛豫的主导机理.退火(Ga,Mn)As的超快克尔增强效应显示其在超高速全光自旋开关方面的潜在应用价值,也为(Ga,Mn)As铁磁性起源的p-d交换机理提供了证据. 关键词： (Ga Mn)As稀磁半导体 时间分辨克尔光谱 电子自旋弛豫 DP机理     

ZnS(111)表面掺杂Mn的电子结构和磁性的第一性原理研究

应用基于密度泛函理论的第一性原理,研究Mn原子掺杂在ZnS(111)表面的电子结构和磁性.对于单原子的掺杂组态,替位表面第一层的Zn原子时体系形成能最低,说明该层是最稳定的掺杂位置.体系总磁矩取决于Mn原子的局域环境.而对于双掺杂组态,当Mn与Mn之间呈短程铁磁耦合作用时体系最稳定.这可由Mn原子和近邻S原子的p-d杂化作用解释.此时,体系的居里温度估算值为469 K,明显高于室温,具有理论指导意义.Mn原子和受主半导体之间的相互作用是自旋极化产生的主要原因.计算结果表明,该掺杂材料可以很好的用来制作稀磁半导体,具有良好的应用前景.     

稀磁半导体(Ga,Mn)As薄膜激光诱导超快磁化动力学过程拟合方法探究

本文对稀磁半导体(Ga, Mn)As薄膜中超快激光诱导磁化动力学响应信号的不同拟合方法进行了对比分析. 通过Landau-Lifshitz-Gilbert(LLG)方程的数值拟合发现, 由于薄膜平面内和平面外磁光响应强度不同, 磁矢量三维进动的叠加可以导致多个频率振动模式的假象. 当使用高于(Ga, Mn)As带边的能量激发时, 磁化进动的磁光响应信号中叠加着来自光极化载流子的响应, 此时单纯利用LLG方程对薄膜整体磁化动力学过程拟合应谨慎使用. 本工作为正确分析和理解脉冲激光对(Ga, Mn)As铁磁性的超快调控提供了拟合方法上的指导.     

Mn掺杂ZnS(110)表面的电子结构和磁性

采用基于密度泛函理论的第-性原理方法,研究Mn掺杂ZnS(110)表面的电子结构和磁性.计算分析不同掺杂组态的几何参数、形成能、磁矩、电子态密度以及电荷密度.结果表明:单个Mn原子掺杂,替位于表面第二层的Zn原子时体系形成能最低,说明该层是最稳定的掺杂位置.对于两个Mn原子的掺杂,当Mn与Mn之间呈反铁磁耦合时体系最稳定.体系的总磁矩和自由Mn原子的磁矩差别很小,但是Mn原子的局域磁矩却依赖于Mn原子的3d态和近邻S原子的3p态的杂化作用,即受周围S原子环境的变化影响较大.此外,分析电荷密度图得出Mn原子替换Zn原子后与S原子形成了更强的共价键.     

第一原理计算稀磁半导体(In1-xMnx)As的晶格常数,磁性和电子结构

用紧束缚近似线性Muffin-tin轨道的方法计算了稀磁半导体(In1-xMnx)As(x=1/2,1/4和1/8)的晶格常数,磁性和电子结构.给出了Mn掺杂浓度的变化对(In1-xMnx)As的晶格常数,磁性和电子结构的影响.     

Co掺杂(ZnO)12团簇的结构和磁性质

采用第一性原理密度泛函理论系统地研究Co原子单掺杂和双掺杂(ZnO)₁₂团簇的结构和磁性质.考虑三种掺杂方式:替代掺杂,外掺杂和内掺杂.首先比较各种掺杂团簇的稳定性.结果表明,不管是单掺杂还是双掺杂,外掺杂团簇都是最稳定结构.在结构优化的基础上,对掺杂的(ZnO)₁₂团簇进行磁性计算.发现团簇磁矩主要来自Co-3d态的贡献,4s和4p态也贡献了一小部分磁矩.由于轨道杂化,相邻的Zn和O原子也产生少量自旋.Co原子之间的磁性耦合由直接的Co-Co反铁磁耦合和Co和O原子之间通过p-d杂化产生的铁磁耦合这两种相互作用的竞争决定.研究发现外双掺杂团簇存在铁磁耦合,在纳米量子器件有潜在的应用价值.     

MnTe电子结构和磁性的第一性原理研究

采用基于密度泛函理论的赝势投影缀加波方法, 对六种典型的二元晶体结构Rocksalt (RS), Cesiun-chloride (CC), Zinc-blende (ZB), Wurtzite (WZ), Iron-silicide (IS) 和Nickel-Arsenide (NA)的MnTe进行了计算研究. 通过比较六种结构的结合能, 确定了MnTe的基态结构是反铁磁的NA结构. 研究了这六种结构MnTe的电子结构、磁性, 并用Birch-Murnaghan状态方程拟合求得了各相结构的体弹性模量和相变压. 电子态密度表明, RS, CC和IS结构的MnTe为反铁磁导体, ZB, WZ和NA结构的MnTe均为反铁磁半导体.     

稀磁半导体(Ga1-xFex)As的电子结构,磁性及其稳定性的第一性原理研究

采用基于第一性原理的紧束缚近似线性muffin-tin轨道(TB-LMTO-ASA)的方法,在原子球近似的基础上计算了均匀掺杂的稀磁半导体(Ga1-xFex)As在各掺杂浓度下(x=1,1/2,1/4和1/8)的总能量,由能量最低原理得到其在各稳定点的晶格常数,磁性及相应态密度.计算结果表明了(Ga1-xFex)As的晶格常数随掺杂浓度的增大而减小,在各掺杂浓度下(除x=1)样品都是反铁磁态的,Fe 3d和As 4p之间杂化是引起样品电子结构和磁性变化的主要原因.     

F原子吸附TiO_2:Mn(001)稀磁半导体薄膜电子结构和磁性的第一性原理计算

利用第一性原理方法计算Mn离子掺杂纯净TiO2(001)和F原子吸附的TiO2(001)薄膜的形成能、态密度和磁矩.F原子吸附明显降低TiO2∶Mn薄膜体系的形成能.F原子的吸附导致Mn离子的磁矩减小,而表面O原子的磁矩增大.表面O原子的磁矩主要来源于O原子p x和p y轨道的自旋极化,研究表明表面吸附F原子更有利于Mn离子的掺杂,在一定程度上有利于获得结构稳定的铁磁态半金属特性的TiO2∶Mn薄膜.     

Uniaxial strain-dependent magnetic and electronic properties of (Ga,Mn)As nanowires

Variations in magnetic and electronic properties as a function of uniaxial strain in wurtzite(Ga,Mn)As nanowires(NWs) grown along the [0001] direction were investigated based on density functional theory(DFT). We found that(Ga,Mn)As NWs are half-metal, and the ferromagnetic state is their stable ground state. The magnetism of the NWs is significantly affected by the strain and by the substituent position of Mn impurities. By examining charge densities near the Fermi level, we found that strain can regulate the conductive region of the NWs. More interestingly, the size of spin-down band gap of the NWs is tunable by adjusting uniaxial stress, and the NWs can be converted from indirect to direct band gap under tension.     

Annealing effect on magnetic anisotropy in ultrathin（Ga,Mn）As

We investigated the effect of low temperature annealing on magnetic anisotropy in 7-nm ultrathin Ga0.94Mn0.06As devices by measuring the angle-dependent planar Hall resistance(PHR).Obvious hysteresis loops were observed during the magnetization reversal through the clockwise and counterclockwise rotations under low magnetic fields(below 1000 Gs,1 Gs = 10-4 T),which can be explained by competition between Zeeman energy and magnetic anisotropic energy.It is found that the uniaxial anisotropy is dominant in the whole measured ferromagnetic range for both the as-grown ultrathin Ga0.94Mn0.06As and the annealed one.The cubic anisotropy changes more than the uniaxial anisotropy in the measured temperature ranges after annealing.This gives a useful way to tune the magnetic anisotropy of ultrathin(Ga,Mn)As devices.     

Magnetic properties of (Ga,Mn)N ternaries and structural,electronic, and magnetic properties of cation-mixed (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries

ABINIT simulation package with built in local density, generalized gradient, and spin local density approximations was used to investigate the structural, electronic, and magnetic properties of cation mixed (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries with equal and fixed compositions of Ga, In, and Mn atoms. In particular, total energy minimization approach was used to compute the equilibrium structural parameters of zinc-blende (GaAs, InAs, and MnAs), wurtzite (GaN, InN, and MnN) binary parent compounds, as well as, the corresponding equilibrium parameters of (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternary systems. The band structures of zinc-blende GaAs, InAs, and MnAs binary parent compounds were computed and analyzed. Spin polarized band structures of the cation mixed (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries with equal compositions of Ga, In, and Mn cations were computed and analyzed using spin local density approximation based calculations. Moreover, the magnetic properties of (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries with equal concentration of Ga, In, and Mn cations were investigated. Our results suggest that the two quaternary systems are nonmagnetic. An interpretation of our results is presented. In addition, the magnetic properties of (Ga,Mn)N nanocrystal ternaries constructed from doping GaN with one or two Mn atoms were investigated using Vienna Ab-initio Simulation Package (VASP) and compared with those of (Ga,Mn)(As,N) quaternaries.     

掺Ga对ZnO电子态密度和光学性质的影响

采用密度泛函理论下的第一性原理平面波赝势方法,研究了掺Ga对纤锌矿ZnO电子态密度和光学性质的影响.从晶体配位场理论分析了掺Ga前后ZnO的成键情况及态密度的变化.计算得到掺Ga后电子浓度为2.42×10²¹ cm^-3,ZnO的载流子浓度提高了10⁴倍.比较分析掺Ga前后ZnO的介电函数、复折射率、吸收光谱和反射光谱可得,ZnO光吸收边向高能端移动,光学带隙增大.在可见光区,ZnO光吸收系数与反射率减小,光透过率显著提高,使ZnO:Ga成为 关键词： 密度泛函理论 态密度 光学性质 ZnO:Ga     

(In, Mn)As nanowires with ultrahigh Mn concentration: Growth, morphology and magnetic anisotropy

(In,Mn)As nanowires with ultrahigh Mn concentration have been successfully grown on GaAs(001) substrates by molecular beam epitaxy. The morphology dependences on Mn concentration and growth temperature are investigated. High Mn concentration and high growth temperature are both necessary for the growth of nanowires. All the (In,Mn)As nanowires are self-aligned along [−110]GaAs, and therefore have the shape magnetic anisotropy with the easy axis along the alignment orientation of the nanowires.     

Structure, electronic and magnetic properties of Cr-doped (ZnS)12 clusters: A first-principles study

We have studied the structural, electronic, and magnetic properties of (ZnS)₁₂ clusters doped with one (monodoped) and two (bidoped) Cr atoms in terms of a first-principles method. Substitutional, exohedral, and endohedral doping are considered. The substitutional isomer is found to be most favorable in energy for monodoped clusters, while the exohedral isomers are found to be most favorable for bidoped clusters. The magnetic coupling between the Cr atoms is mainly governed by the competition between direct Cr-Cr antiferromagnetic (AFM) interaction and the ferromagnetic (FM) interaction between two Cr atoms via S atom due to strong p-d hybridization. Finally, we show that the exohedral bidoped (ZnS)₁₂ clusters favor the FM state, which has potential applications in nanoscale quantum devices.     

高质量稀磁半导体(Ga,Mn)Sb单晶薄膜分子束外延生长

理论预言窄禁带稀磁半导体(Ga,Mn)Sb及其异质结构可能存在量子反常霍尔效应等新奇特性, 近年来受到了特别关注. 但是, 由于(Ga,Mn)Sb薄膜生长窗口窄, 纯相(Ga,Mn)Sb薄膜制备比较困难, 迄今关于这类材料的研究报道为数不多. 本文采用低温分子束外延的方法, 通过优化生长条件, 成功制备出厚度为10 nm, Mn含量在0.016至0.039之间的多组(Ga,Mn)Sb薄膜样品. 生长过程中反射式高能电子衍射原位监测和磁性测量都表明没有MnSb等杂相的偏析, 同时原子力显微镜图像表明其表面形貌平滑, 粗糙度小. 通过生长后退火处理, (Ga,Mn)Sb薄膜的最高居里温度达到30 K. 此外, 本文研究了霍尔电阻和薄膜电阻随磁场的变化关系, 在低温下观测到明显的反常霍尔效应.