Ni纳米线的结构和性质研究

采用推广模拟退火算法(Generalized Simulated Annealing,GSA)和Sutton-Chen势,研究了初始构型为面心立方(fcc)结构的Ni纳米线,在沿径向压缩时的结构和性质.结果表明:径向压缩程度对Ni纳米线的结构有很大的影响.当Ni纳米线直径大于0.398nm时(初始直径为0.498nm),其结构由fcc结构变为类似fcc结构,但结合能变化很小,表明其结构之间几乎可以实现零能量转换,且稳定性基本不变;当Ni纳米线直径小于0.398nm时,其结构从无定形结构变为缺陷结构,结合能迅速上升,表明其结构稳定性降低;键角的分布也证明了以上结果的正确性.     

Tunable magnetic properties of arrays of Fe(1 1 0) nanowires grown on kinetically grooved W(1 1 0) self-organized templates

We report a detailed magnetic study of a new type of self-organized nanowires discussed briefly previously [B. Borca et al., Appl. Phys. Lett. 90 (2007) 142507]. The templates, prepared on sapphire wafers in a kinetically limited regime, consist of uniaxially grooved W(1 1 0) surfaces, with a lateral period here tuned to 15 nm. Fe deposition leads to the formation of (1 1 0) 7 nm-wide wires located at the bottom of the grooves. The effect of capping layers (Mo, Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was studied. Significant discrepancies with figures known for thin flat films are evidenced and discussed in terms of step anisotropy and strain-dependent surface anisotropy. Demagnetizing coefficients of cylinders with a triangular isosceles cross-section have also been calculated, to estimate the contribution of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the interface element was used to tune the blocking temperature of the wires, here from 50 to 200 K.     

Arrays of Ni nanowires in alumina membranes: magnetic properties and spatial ordering

Magnetic characteristics of arrays of Ni nanowires embedded in porous alumina are reviewed as a function of their spatial ordering. The different steps for the controlled production of highly-ordered nanowires is firstly described. Nanopores are formed into an hexagonal symmetry arrangement by self-organized process during anodization of pure Al. Parameters of the anodization allow us to control their diameter, hexagonal lattice parameter and size of crystalline domains. Subsequently, Ni nanowires are grown inside the pores by electrodeposition. Control of the pores filling and of geometrical ordering characteristics has been performed by SEM, HRSEM, RBS and AFM techniques. The magnetic characterisation of the arrays has been achieved by SQUID and VSM magnetometers, while information on the magnetic state of individual nanowires is obtained by MFM. Experimental studies are presented, particularly coercivity and remanence, for arrays with different degree of ordering (crystalline domains up to around 1 m), and for ratio diameter to lattice parameter (diameter ranging between 20 and 180 nm, and distance between 35 and 500 nm). FMR studies have allows us to obtain complementary information of the anisotropy and magnetic characteristics. A modelling of multipolar interacting nanowires is introduced to account for the influence of short and long range ordering degree of the arrays.Received: 24 November 2003, Published online: 15 June 2004PACS: 75.60.Jk Magnetization reversal mechanisms - 81.15.Pq Electrodeposition, electroplating     

Quantized field-electron emission at 300 K in self-assembled arrays of silicon nanowires

Dense ensembles of silicon nanowires were prepared by metal-catalyzed chemical vapor deposition on silicon substrates. Some of these ensembles were doped with phosphorous during growth. The nanowires were characterized using scanning electron microscopy, X-ray diffraction, and mass spectroscopy. Field emission of electrons from these structures was studied at room temperatures in ultra-high vacuum. The measurements were carried out using a parallel-plate diode cell. At high-applied fields, the current–voltage characteristics deviate from the Fowler–Nordheim law and exhibit a step-wise increase in the current with the increasing voltage at 300 K. Possible mechanisms of the observed quantized field emission are discussed.     

Synthesis and magnetic properties of multilayer Ni/Cu and NiFe/Cu nanowires

Highly ordered composite nanowires with multilayer Ni/Cu and NiFe/Cu have been fabricated by pulsed electrodeposition into nanoporous alumina membrane. The diameter of wires can be easily varied by pore size of alumina, ranging from 30 to 100 nm. The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer (VSM) measurements. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated domain-like magnet. This technique has potential use in the measurement and application of magnetic nanodevices.     

Effect of oxidation on the magnetic properties of Ni3Cr alloy

The effect of oxidation on magnetic susceptibility and electrical resistance was studied in samples of Ni₃Cr alloy which had been prehardened from 1066, 1190, and 1250°C. X-radio-graphic analysis of the samples was carried out. It was shown that the observed increase of the magnetic susceptibility of the alloy after oxidation in the temperature range 750–1050°C is related to the formation on the surface of the sample of a layer with a variable nickel content in the range Ni₃Cr to pure nickel.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 38–41, May, 1972.     

Effect of annealing on the magnetic and magnetooptical properties of Ni films

The magnetic and magnetooptical properties of 50-to 200-nm-thick Ni films, both as-deposited and annealed at T_ann = 300, 400, or 500°C, were studied. Volume and near-surface hysteresis loops were measured with a vibrating-sample magnetometer (VSM) and with the use of the transverse Kerr effect (TKE). The annealing temperature was found to exert a strong effect on the magnetic characteristics of the samples under study. It was established, in particular, that the coercivity H _C of Ni films increases and the remanent magnetization decreases with increasing annealing temperature. The observed dependences of the magnetic properties of the films on film thickness and annealing temperature are explained as being due to microstructural characteristics of the samples. It was found that, while TKE spectra obtained in the incident-photon energy region from 1.5 to 6 eV have the same shape for all the Ni films studied, the magnitude of the TKE decreases with increasing T_ann. This experimental observation is accounted for by the decreased saturation magnetization of the annealed films.     

Effects of silicon nanowires length on solar cells photovoltaic properties

Silicon nanowires (SiNWs) were produced by an electroless method on FZ-Si (100) wafer, in HF/AgNO₃ solution. The influence of etching time and temperature on SiNWs morphology were studied using FESEM images. Optical properties were also investigated by optical absorption spectroscopy and low-temperature photoluminescence at 4.2?K. Considering their role as active regions, photovoltaic properties of SiNWs solar cells were studied for their different lengths. Photovoltaic measurements were taken in 1 sun condition under AM 1.5 illumination supplied by a solar simulator. Measurements indicated a reduction in efficiency as SiNWs length increased, which might be attributed to increased dangling states on nanowires surfaces.     

Ni掺杂对ZnO磁光性能的影响

在掺杂浓度范围为2.78%—6.25%(物质的量分数)时,Ni掺杂ZnO体系吸收光谱分布的实验结果存在争议,目前仍然没有合理的理论解释.为了解决存在的争议,在电子自旋极化状态下,采用密度泛函理论框架下的第一性原理平面波超软赝势方法,构建不同Ni掺杂量的ZnO超胞模型,分别对模型进行几何结构优化和能量计算.结果表明,Ni掺杂量越大,形成能越高,掺杂越难,体系稳定性越低,掺杂体系带隙越窄,吸收光谱红移越显著.采用LDA(局域密度近似)+U方法调整带隙.结果表明,掺杂体系的铁磁性居里温度能够达到室温以上,磁矩来源于p-d态杂化电子交换作用.Ni掺杂量越高,掺杂体系的磁矩越小.另外还发现Ni原子在ZnO中间隙掺杂时,掺杂体系在紫外光和可见光区的吸收光谱发生蓝移现象.     

Effect of Ni doping on the structural and magnetic properties of FePt nanoparticles

A serial of FePtNi nanoparticles were investigated on their crystal structure and magnetic properties. The FePtNi nanoparticles were synthesized simultaneously by the reduction of iron (III) acetylacetonate, platinum (II) acetylacetonate and nickel (II) acetylacetonate with 1,2-hexadecanediol as the reducing agent. The X-ray diffraction patterns indicate that the addition of 8, 12, 17 at% Ni in FePt nanoparticles suppressed the transformation of the particles from disorder face-centered cubic to order face-centered tetragonal L1₀-phase under annealing treatment. However, further increasing Ni contents to 21 at%, the nanoparticle transformed to L1₂ phase. Doping of Ni into the FePt compound system may decrease coercivity and crystal anisotropy energy. A maximum coercivity of 7 KOe at room temperature was obtained for (Fe₅₂Pt₄₈)₉₂Ni₈ nanoparticles after annealing at 600 °C for 30 min.     

Microstructural and magnetic properties of CoPt nanowires

In this work, the magnetic and microstructural properties of CoPt nanowires are presented as a function of the electrolyte pH and current density during electrodeposition into anodized alumina templates. CoPt nanowires of high aspect ratio have been prepared using electrolyte pH values in the range from 2 to 6. The as-made samples exhibit a face centered cubic (fcc) structure with soft magnetic properties which transform into the face centered tetragonal (fct) L10 phase after thermal treatment. Different pH values of the electrolyte during electrodeposition lead to significantly different microstructures and, therefore, different magnetic properties. The CoPt nanowires prepared at high pH value are composed of fcc nanorods of about 25 nm in length. Thermal annealing of these samples leads to a preferred (0 0 1) orientation (along the direction perpendicular to the direction of nanowires) which increases with annealing time. On the other hand, the CoPt nanowires prepared at lower pH value are composed of uniform fcc nanograins with the size ∼2−3 nm. Magnetization curves for the later sample are virtually identical in both directions indicating an isotropic behavior.     

Ordered arrays of Ni magnetic nanowires: Synthesis and investigation

The present study is focused on the synthesis and investigation of anodic aluminum oxide (AAO) films and magnetic nanocomposites Ni/AAO obtained by Ni electrodeposition into porous matrix. AAO membranes and magnetic nanocomposites were investigated by HRSEM, EDX microanalysis, XRD, nitrogen capillary adsorption method, SQUID magnetometry, and polarized small-angle neutron scattering (SANS). The influence of synthesis conditions and form factor effect on the magnetic properties of nanowire arrays is reported.     

Oxygen on Fe(1 1 0): magnetic properties of the adsorbate system

Investigations concerning the electronic and magnetic properties of oxygen adsorbed on magnetized iron films were carried out by means of angle and spin resolving photoelectron spectroscopy. Iron(1 1 0), epitaxially grown on a W(1 1 0) crystal, served as the ferromagnetic substrate. Exchange splittings of the O 2p_x derived level were detected demonstrating a magnetic coupling between the chemisorbate and the iron layer. This observation indicates the presence of an induced magnetic moment within the adsorbate overlayer. Variations of the exchange splitting occurred as a function of the oxygen coverage, energy of the exciting radiation, and detection angle of the emitted photoelectrons pointing to a k₆-dependent exchange splitting. High oxygen exposures lead to a FeO overlayer at the surface, showing vanishing peak separations due to the antiferromagnetic behavior of iron oxide.     

Effect of annealing treatment on soft magnetic properties of Fe-6.5 wt% Si wide ribbons

The 25 mm wide ribbons of Fe-6.5 wt% Si alloy have been developed by melt spinning technique, showing sufficient ductility and white silver appearance. Two magnetic transitions take place at 676 and 760 °C due to the formation of B2 ordered phase and A2 disordered paramagnetic phase, respectively. The saturation magnetization of the ribbon is 17.5 kG under the applied field of 12 kG. The as-cast ribbons consist of disordered A2 structure with a low volume of B2 phases while the annealed microstructure comprises a dispersion of B2 domains in the disordered A2 matrix. The alloy shows the enhancement of the soft magnetic properties with a reduction in coercivity from 150 A/m in the as-cast state to 45 A/m in the annealed condition at 850 °C.     

Effect of Nd ion on the magnetic properties of Ni–Mn ferrite nanocrystal

The nanocrystalline Ni_0.7Mn_0.3Nd_0.1Fe_1.9O₄ ferrites were prepared by the emulsion method. X-ray diffractometer (XRD), transmission electron microscope (TEM), Mössbauer spectra and vibrating samples magnetometer (VSM) were used to study the structure, morphology and magnetic properties. The magnetic properties of Nd³⁺-doped Ni_0.7Mn_0.3Fe₂O₄ nanocrystal ferrites were investigated in detail. The Ni_0.7Mn_0.3Nd_0.1Fe_1.9O₄ nanocrystal ferrite with particle size of 10.7 nm shows superparamagnetism.     

Cr掺杂ZnO纳米线电子性质和磁性质

本文采用第一性原理密度泛函理论系统的研究了Cr原子单掺杂和双掺杂两种尺寸ZnO纳米线的电子性质和磁性质.所有掺杂纳米线的形成能都比纯纳米线的形成能低,表明掺杂增强了纳米线的稳定性.研究发现Cr原子趋于替代纳米线表面的Zn原子.所有掺杂纳米线都显示了金属性.纳米线的总磁矩主要来源于Cr原子3d轨道的贡献.由于杂化,相邻的O原子和Zn原子也产生了少量自旋.在超原胞内,Cr和O原子磁矩反平行排列,表明它们之间是反铁磁耦合.表面双掺杂纳米线铁磁态能量比反铁磁态能量低149 meV,表明Cr掺杂ZnO纳米线可能获得室温铁磁性.     

On the range of interaction from finite size scaling in magnetic Ni nanowires

A recent experiment reporting a thickness dependence of magnetic properties of Ni nanowires has been re-interpreted in terms of spin–spin interactions eventually ranging beyond nearest neighbors. An analysis following the Ginzburg argument indicated that the system is in the crossover regime from 3D Ising to classical critical behavior as a function of the normalized range of interactions R$R$. The range of the interactions covering three to four coordination spheres of an Ni atom has been found by the fit to literature experimental data on Ni nanowires. Consistency with recent first-principles calculations are discussed.     

Photoluminescence of ZnO nanowires grown on sapphire (1 1 2¯ 0) substrates

ZnO nanowires were fabricated on c-plane (0 0 0 1), a-plane (1 1 2¯ 0) sapphire, and boron doped p-type (1 0 0) Si substrates in vacuum furnace by simple physical vapor deposition. Room temperature photoluminescence spectra of the nanowires show the near band-edge emission and the deep-level green light emission. The ZnO nanowires formed on sapphire (1 1 2¯ 0) substrates exhibited enhancement on optical properties and better crystalline structures than those of nanowires grown on other substrates. The formation mechanism and the effect of substrate direction on structural and optical properties of the nanowires are discussed.     

Effect of bilayer repeats on magnetic properties of Au-buffered Co/Ni multilayers with perpendicular magnetic anisotropy

The effect of bilayer repeats (N) on the static and dynamic magnetic properties of Co/Ni multilayers was investigated. The effective perpendicular magnetic anisotropy constant of multilayers drops from $1.08\times {10}^6$ erg/cm³ to $0.78\times {10}^6$ erg/cm³ with N increasing from 5 to 11. For Co/Ni multilayers with $N\le 7$, sharp magnetization switching was observed. In contrast, Co/Ni multilayers with $N\ge 9$ have a long tail in the hysteresis loop. Ferromagnetic resonance measurements show that intrinsic Gilbert damping changes from 0.021 to 0.016 with increase in N and is inversely proportional to N. This study provides a deep understanding and effective control of magnetic properties of Co/Ni multilayers for spintronics devices.