反应磁控溅射氧化镍薄膜的自旋塞贝克效应

自旋塞贝克效应是由(亚)铁磁体中的温度梯度引起自旋塞贝克电压信号的现象,目前已成为热自旋电子学研究的热点领域之一。本文采用反应磁控溅射工艺在Si衬底上沉积NiO薄膜,分别研究了溅射功率、氧氩比例、溅射气压、衬底温度对NiO薄膜微观结构和表面形貌的影响,实验中反应磁控溅射最适工艺条件为溅射功率110 W、氧氩比例0.15(O₂ 15 mL/min; Ar 100 mL/min)、溅射气压0.3 Pa、衬底温度400 ℃。研究了Si/NiO/Pt结构中温度梯度(温差)、磁场角度、NiO厚度变化和Pt厚度变化对自旋塞贝克电压的影响。结果表明,自旋塞贝克电压与温差呈简单的线性关系,温差越大测得的自旋塞贝克电压越高;磁场角度与自旋塞贝克电压之间满足余弦函数关系式,即在0°和180°时所得自旋塞贝克电压最大,90°和270°时为零;反铁磁性绝缘层NiO的厚度越大,所测得的自旋塞贝克电压信号越强;顺磁金属层Pt的厚度越大,自旋塞贝克电压信号越弱。     

MnGa合金体的电子结构与磁性质的研究

基于密度泛函理论方法系统研究了四方结构MnGa合金体的结构、形成、电子结构和磁性质。结果表明,四方MnGa合金晶胞的生成焓为-4.85 eV,高于一些不含d电子的体系。其呈现导体的能带结构,其中d电子主要形成深能级价带,定域性最强。四方MnGa合金存在着明显的自旋极化,靠近费米能级两侧的s电子和靠近费米能级下方的p电子具有较弱的自旋极化。形成浅能级价带和导带的d电子产生高强度的自旋极化,对磁性质贡献较大。Mn的s电子和Mn的p电子自旋极化作用较弱,Mn的d电子形成浅能级价带和导带,自旋极化作用最强。形成深能级价带的Ga的d电子自旋极化作用较弱,不同位置的Ga原子的自旋极化不同。四方MnGa合金体具有净有效磁矩,呈弱的亚铁磁性。     

Attractive Interactions of Spin Polarons in the Quasi-One-Dimensional Spin-Density-Wave Background

Abstract

The dynamics of spin polarons (spin bags) in the quasi-one- dimensional spin-density-wave background is numerically studied using the extended Peierls-Hubbard model. Interchain couplings are incorporated to the model as a staggered magnetic field. Time-dependent unrestricted Hartree-Fock equations and Newtonian equations are solved using Suzuki's decomposition of exponential operators. In the Hubbard model, the spin polarons with antiparallel spin polarizations attract each other. When the nearest-neighbor Coulomb repulsion is included, the interaction changes to a repulsive type. Further addition of an intersite electron-phonon coupling leads to an attractive interaction.     

Li原子掺杂C28单分子器件的热自旋输运性质

利用第一性原理对Li原子掺杂C₂₈的分子器件的热自旋输运性质进行了计算。在不同的温度场下,上下自旋分别为Li原子掺杂C₂₈的分子器件中的空穴和电子提供了输运通道,在MJ₁和MJ₃分子器件中,热自旋电流随着温度增加而增大,但在MJ₂分子器件中,热自旋电流先增大再减小。三种分子器件都出现了自旋塞贝克效应,MJ₂还出现了负微分电阻现象,利用费米-狄拉克分布和自旋输运谱对其物理机理进行了解释。根据Li掺杂C₂₈的单分子器件的热自旋输运性质,可设计新的自旋纳米器件。     

EPR Studies of Electron Spin Polarization of Triplet Exciton and its Transfer into Triplet Traps of Naphthalene-TCNQ and Naphthalene-pChloranil Guest Complexes in the Naphthalene-TCNB Host

The EPR spectra of triplet excitons in single crystals of Naphthalene-TCNB (N-TCNB) charge-transfer (CT) complexes show optical electron spin polarization (OEP) which is accounted for by a spin selective populating process from the excited CT singlet into an excited triplet state localized on the acceptor. OEP is also observed for triplet traps in N-TCNB crystals doped with TCNQ and pChloranil. The analysis of the orientation dependence of spin polarization allows one to establish that also selective decay from the trap spin sublevels is important for the onset of the observed OEP features.     

Electron spin resonance studies of microcrystalline and amorphous silicon irradiated with high energy electrons

Paramagnetic defects in μc-Si:H and a-Si:H with various structure compositions were investigated by electron spin resonance (ESR). The defect density was varied by high energy electron bombardment and subsequent annealing. The spin density increases by up to 3 orders of magnitude. In most cases the initial spin density can be restored upon annealing at 160 °C.     

The Orientational Order of a Re-entrant Nematic Phase. an Electron Resonance Investigation

We have investigated the orientational order in a re-entrant nematic and its preceding phases using steroidal and alkyl nitroxide spin probes. The order parameter for the steroidal spin probe in the re-entrant nematic phase is found to be an extension of its value in the preceding smectic A phase. In contrast the gradient of the order parameter for the alkyl spin probe exhibits a marked discontinuity at the smectic A - re-entrant nematic transition.     

Temperature dependences of the electric polarization and wave number of incommensurate structures in multiferroics

It is shown that the electric polarization and wave number of incommensurate modulations, proportional to each other, increase according to the Landau law in spin multiferroic cycloids near the Néel temperature. In this case, the constant magnetization component (including the one for a conical spiral) is oriented perpendicular to the spin incommensurability wave vector. A similar temperature behavior should manifest itself for spin helicoids, the axes of which are oriented parallel to the polarization vector but their spin rotation planes are oriented perpendicular to the antiferromagnetic order plane. When the directions of axes of the magnetization helicoid and polarization vector coincide, the latter is quadratic with respect to magnetization and linearly depends on temperature, whereas the incommensurate-modulation wave number barely depends on temperature. Structural distortions of unit cells for multiferroics of different types determine their axial behavior.     

Radiation-induced defects in fluoride glasses

Fluorozirconate (ZBLA) and fluorohafnate (HBL) glasses have been exposed to ionizing radiation at room temperature, and the resulting defects have been characterized using optical absorption and electron spin resonance techniques. Prominent absorption bands were found to peak in the ultraviolet at 290 nm for the ZBLA glass and at 240 and 310 nm for the HBL glass. Two major electron spin resonance spectra having g values of 1.883 and 2.043 were induced in the HBL glass. Similar electron spin resonance spectra were found in the ZBLA glass. A third spectrum with a g value of 2.008 was also observed in the ZBLA material. The optical and electron spin resonance spectra in these glasses thermally annealed between room temperature and 300°C. Possible models for the defects are discussed.     

Current-induced magnetic switching and dynamics in spin valves

Spin torque and current-induced magnetic switching (dynamics) in spin valve nanopillars is considered theoretically in the diffusive transport regime. Basic characteristics of the precessional states are discussed. Current-induced switching in other spin valves is analyzed, particularly in ferromagnetic single-electron transistors based on magnetic molecules.     

Magnetic properties of amorphous metals

Neutron scattering has provided unique information about the nature of magnetism in amorphous alloys. This paper reviews some of the results obtained principally on two ribbon-form metallic glass systems - (Fe_xNi_1?x)₇₅P₁₆B₅Al₃ and Fe_xB_1?x. The former exhibits three states depending on composition: pure ferromagnetism, re-entrant spin glass, and ordinary spin glass. The neutron results provide evidence for the coexistence of spin glass and ferromagnetic correlations in the intermediate regime. The alloys of Fe and B show Invar phenomena which result in anomalously small values of the effective spin-wave stiffness calculated from low-temperature magnetization and Mössbauer data. The long-wavelength spin waves as measured by the neutrons do not reflect the rapid demagnetization found in the bulk results, implying the presence of excitation processes other than long-wave-length spin waves.     

The Interaction of Light with Rb0.73Cr5Te8 and Polymer/Nanoferrite Composites

Abstract

The magnetic and photomagnetic characterizations of two materials are reported: ploymer/nanoferrite composites and the non-stoichiometric crystalline materials Rb0.73Cr5Te8. In the inorganic-organic composite material, the inorganic component is iron oxide and the organic component is the polymer poly(p-ethylphenol) (PEP). The Rb0.73Cr5Te8 material is a new non-stoichiometric formulation of the ACr5Te8 system that exhibits spin glass type magnetic behavior with a spin glass freezing temperature of 175K. The photomagnetism of both compounds has been measured at several temperatures below the spin blocking temperature.     

完全Heusler合金Cr2ZrSb/Sc2FeSn(100)异质结的结构、电磁特性及电子性质

本文采用基于密度泛函理论的第一性原理计算,系统研究了完全Heusler合金Cr₂ZrSb/Sc₂FeSn(100)异质结中六种界面CrCr-ScFe-T、ZrSb-ScSn-T、CrCr-ScSn-B、ZrSb-ScFe-B、CrCr-ScFe-V和 ZrSb-ScSn-V的电磁特性及电子性质。结果表明,界面原子间的相互作用造成了界面间原子层的不均匀,导致界面层的力学失配率加大。与块体中的高自旋极化率相比,异质结的自旋极化率遭到不同程度的破坏。但是,ZrSb-ScFe-B界面保留了较高的自旋极化率值,通过Julliere模型预测该异质结在低温下隧道磁电阻值约为429.29%,在自旋电子学器件中具有潜在的应用前景。     

Vitrification,relaxation and free volume in glycerol–water binary liquid mixture: Spin probe ESR studies

Glass transition and relaxation of the glycerol–water (G–W) binary mixture system have been studied over the glycerol concentration range of 5–85 mol% by using the highly sensitive technique of electron spin resonance (ESR). For the water rich mixture the glass transition, sensed by the dissolved spin probe, arises from the vitrified mesoscopic portion of the binary system. The concentration dependence of the glass transition temperature manifests a closely related molecular level cooperativity in the system. A drastic change in the mesoscopic structure of the system at the critical concentration of 40 mol% is confirmed by an estimation of the spin probe effective volume in a temperature range where the tracer reorientation is strongly coupled to the system dynamics.     

Spin relaxation in nanophased manganites

We present recent results obtained by DC and AC susceptibility, muon spin relaxation and neutron spin echo experiments in magnetically ordered La_0.7Pb_0.3MnO₃ and disordered La_0.7Pb_0.3Mn_0.8Fe_0.2O₃. These results aim to cover an extraordinary equivalent frequency range (from quasi-static experiments to almost the THz region) and give an overall picture of the processes within. The different relaxations observed are related either to the macroscopic long-ranged interactions among magnetic clusters (susceptibility techniques) and to short-ranged intracluster spin diffusion processes (muon and neutron techniques).     

Frequency Dependence of ESR in Pristine Trans-Polyacetylene: Line Width

We measured a frequency dependence of ESR line width in (CH)x and (CD)x at frequencies 5～9,500 MHz. From a detailed analysis we could independently deduce 1-D diffusion rate of electron spin (neutral soliton) D_‖ /c_‖ ², and the trapped spin concentration C between 200 and 340 K.     

Spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated bis(acetylacetonato)palladium(II)

This paper reports on a theoretical analysis of spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated Pd(II)(acac)₂. Through the crystal‐ and ligand‐field theory, the microscopic spin‐Hamiltonian parameters and local molecular structure for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system have been studied by using the high‐order perturbation formulas and Newman's superposition model. Based on these calculations, it was found that the distance of the metal‐ligand bonds in the square planar complex for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system increases by 0.1Å. To understand the detailed physical and chemical properties of the [Pd(I)(acac)₂]^2– complex, the contributions of the spin‐orbit coupling of ligand to spin‐Hamiltonian parameters for Pd(I) ion are considered. The theoretical results are in reasonable agreement with the experimental values. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoluminescence of geminate and non-geminate pairs in amorphous semiconductors

Rates of radiative recombination of geminate and non-geminate pairs and the corresponding lifetimes are calculated at thermal equilibrium. It is shown that two kinds of geminate recombinations occur in amorphous semiconductors: (I) through the recombination of the usual geminate pairs (non-excitonic) and (II) through the recombination of those excitons that have relaxed to the tail states. The latter geminate pairs can exist in singlet and triplet spin states, only singlet is considered here, whereas former ones do not have spin dependence. Examples of recent observations and their comparison with the theoretical results are presented.     

CuSCN空穴传输层工艺对钙钛矿电池性能的影响

采用溶液法制备了硫氰酸亚铜(CuSCN)薄膜,并将其作为空穴传输层制备了平面n-i-p型钙钛矿太阳电池.系统考察了CuSCN薄膜退火温度、旋涂转速对钙钛矿太阳电池性能的影响.研究结果表明,CuSCN薄膜在70 ℃下退火10 min可以获得较好的电池性能;在此基础上通过调整旋涂转速至2000 r/min,控制CuSCN薄膜厚度约为240 nm,电池性能获得了进一步的提升,电池效率可达11.77;.该研究结果表明,CuSCN材料是一种有潜力的、低成本高性能无机空穴传输材料.     

Dynamical magnetic correlations in the YbB12 kondo insulator: Neutron investigations with a polarization analysis

The results of investigations into the spin dynamics in the YbB₁₂ Kondo insulator with the use of inelastic neutron scattering, including experiments with a polarization analysis, are discussed. It is shown that, at low temperatures, the dynamic magnetic response in the structure of the YbB₁₂ Kondo insulator is characterized by three dispersive excitations with a nontrivial q-dependence of the intensity. An increase in the temperature results in a crossover to the single-site spin fluctuation regime accompanied by suppression of collective excitations.