Controlled Cu content of electrodeposited CoCu nanowires through pulse features and investigations of microstructures and magnetic properties

CoCu alloy nanowire arrays embedded in anodic alumina template were fabricated by ac pulse electrodeposition. Different off-times between pulses in an electrolyte with constant concentration of Co⁺² and Cu⁺² and acidity of 4 were employed. The effect of deposition parameters on the alloy contents, microstructures and magnetic properties of Co_xCu_1−x nanowires were studied. It is shown that Co content decreased by increasing the off-time between pulses in a wide range (x = 0.53-0.07). These results are in consistence with saturation magnetization, which was reduced with increase in the off-time between pulses. It was also found that by optimizing the off-times, it is possible to fabricate CoCu nanowires with mixed phase of hcp Co, fcc Cu and fcc CoCu crystal phase.     

Structure and magnetic properties of CoxPb1−x nanowire arrays

Ordered Co_xPb_1−x nanowire arrays embedded in the porous anodic aluminum oxide (AAO) template have been fabricated by electrodeposition. XRD experiments prove that neither hexagonal-close-packed (hcp) nor face-centered-cubic (fcc) Co peaks are detected when the Co component (x) is below 0.91. The coercivity (H_c) and squareness (M_r/M_s) are found to increase with ferromagnetic Co component and the maximum value is at the position x=1 (pure Co nanowires). Annealing effects cause H_c and M_r/M_s increase, which surpasses the pure Co nanowires in the 0.2<x<0.6 at the annealing temperature of 700 °C. Microstructure change during annealing process is proposed to explain the magnetic properties change of samples.     

磁场对模板法制备的Co纳米线结构和磁性的影响

在用二次氧化法制备的高度有序的氧化铝模板上通过交流电化学方法制备了Co纳米线阵列．研究了外加磁场及电解液pH值对纳米线生长的影响．在pH值为6.0和6.5的电解液中分别在不加磁场和沿纳米线轴向施加0.3 T磁场情况下制备了hcp结构的Co纳米线阵列．实验数据表明,沉积时外加磁场和调节pH值能有效影响纳米线中hcp结构的Co晶粒的易磁化轴沿纳米线长轴方向生长．由于晶粒的磁晶各向异性和纳米线沿长度方向的宏观形状各向异性叠加,制备的Co纳米线阵列具有高垂直各向异性,高矫顽力和较高矩形比． 关键词： Co纳米线阵列 织构 磁性     

Fabrication and magnetic properties of ordered Fe60Pb40 nanowire arrays electrodeposited in AAO templates

Ordered ferromagnetic-nonmagnetic heterogeneous Fe₆₀Pb₄₀ nanowire arrays were successfully fabricated by alternating current (AC) electrodeposition into nanoporous alumina templates. Transmission electron microscopy (TEM) image and selected-area diffraction (SAED) pattern analysis showed that the Fe₆₀Pb₄₀ nanowires are polycrystalline with an average diameter of 22 nm and lengths up to several micrometers. X-ray diffraction (XRD) observations indicated that α-Fe and fcc Pb phase coexist and do not form metastable alloy phase. The as-deposited samples were annealed at 200, 300, 400 and 500 ^°C, respectively. Magnetic measurements showed that nanowires have high magnetic anisotropy with their easy axis parallel to the nanowire arrays, and the coercivity of the samples increased with the annealing temperature up to 400 ^°C and reached a maximum (2650 Oe). The change of magnetic properties associated with the microstructure was discussed.     

Magnetic optical bifunctional CoPt_3/Co multilayered nanowire arrays

CoPt3/Co multilayered nanowire(NW) arrays are synthesized by pulsed electrodeposition into nanoporous anodic aluminum oxide(AAO) templates. The electrochemistry deposition parameters are determined by cyclic voltammetry to realize the well control of the ratio of Co to Pt and the length of every segment. The x-ray diffraction(XRD) patterns show that both Co and CoPt3 NWs exhibit face-centered cubic( fcc) structures. In the UV-visible absorption spectra,CoPt3/Co NW arrays show a red-shift with respect to pure CoPt3 NWs. Compared with the pure Co nanowire arrays, the CoPt3/Co multilayered nanowire arrays show a weak shape anisotropy and well-modulated magnetic properties. CoPt3/Co multilayered nanowires are highly encouraging that new families of bimetallic nanosystems may be developed to meet the needs of nanomaterials in emerging multifunctional nanotechnologies.     

Magnetic and magnetization properties of electrodeposited fcc CoPt nanowire arrays

Magnetic and magnetization properties of fcc Co_1−xPt_x (x?0.3) alloy nanowires fabricated by electrodeposition into self-synthesized anodic alumina templates are investigated. Magnetization curves, measured for varying wire geometries, show a crossover of easy axis of magnetization from parallel to perpendicular to the nanowire axis as a function of the diameter and length. The measured values of coercivity (H_c) and remanent squareness (SQ) of CoPt nanowire arrays, as a function of angle (θ) between the field and wire axis, support the crossover of easy axis of magnetization. The curling mode of the magnetization reversal process is observed for CoPt nanowire arrays. At low temperatures, the easy axis for magnetization of the nanowires is observed to deviate from the room-temperature orientation.     

Fabrication and magnetic properties of Fe-Pd nanowire arrays

Ordered 20 nm Fe-Pd nanowire arrays with different compositions have been fabricated by alternating current electrodeposition into nanoporous anodic alumina. The structural and magnetic properties of the arrays were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). When Fe content is lower than 46 at.%, Fe-Pd alloy phase with fcc structure forms for the as-deposited. After annealing the alloy structure remains unchanged, but the coercivity (H_C) and squareness (M_r/M_s) increase. When Fe content is up to 60 at.%, α-Fe and Fe-Pd phases with fcc structure coexist for the as-deposited. After annealing the nanowires consist of a uniform Fe-Pd phase with fcc structure and the coercivity and squareness decrease. The change of the structure and magnetic properties with the alloy composition and annealing are explained reasonably.     

Template synthesis of single-crystal Cu nanowire arrays by electrodeposition

Cu nanowire arrays have been synthesized using potentiostatic electrodeposition within the confined nanochannels of a porous anodic alumina membrane. The Cu nanowire arrays and the individual nanowires have been characterized using SEM, TEM, SAED, HREM and XRD. Investigation results reveal that the Cu nanowire arrays having high wire packing densities are highly ordered over large areas. The individual Cu nanowires (diameter ∼60 nm) were single-crystal and found to be dense and continuous with uniform diameters throughout their entire length. An optimum ECD condition (at lower overpotentials) for the synthesis of single-crystal Cu nanowires was also discussed. Received: 19 April 2001 / Accepted: 28 April 2001 / Published online: 20 June 2001     

ZnO薄膜的性质对水热生长ZnO纳米线阵列的影响

用水热法在ZnO薄膜上制备了直径、密度及取向可控的ZnO纳米线阵列。ZnO薄膜是通过原子层沉积(ALD)方法制备并在不同温度下退火处理得到的,退火温度对ZnO薄膜的晶粒尺寸、结晶质量和缺陷性质有很大的影响。而ZnO薄膜的性质对随后生长的ZnO纳米线的直径、密度及取向能起到调节控制的作用。通过扫描电子显微镜(SEM)、X射线衍射(XRD)仪和光致发光(PL)测试对ZnO薄膜和ZnO纳米线进行了表征。最后得到的垂直取向的ZnO纳米线阵列适合在发光二极管和太阳能电池等领域使用。     

Pulse electrodeposition of Co1−xZnx nanowire arrays: Magnetic improvement through electrolyte concentration,off-time between pulses and annealing

Using different electrolyte compositions and varying the off-time between pulses, Co_1xZn_x nanowire arrays were fabricated by ac pulse electrodeposition. The effect of deposition parameters on alloy contents was investigated by studying the microstructures and magnetic properties of as-deposited and annealed Co_1xZn_x nanowires. It is shown that Zn content in CoZn nanowires exponentially increases by increasing the zinc ions in the electrolyte. The Zn content initially increases to a maximum by increase in off-time between pulses and then falls off. Adding a certain amount of Zn to Co led to form amorphous CoZn nanowires. A significant increase in magnetization, coercivity and squareness of CoZn nanowires was observed after annealing. The rate of increase in magnetization of annealed samples was seen to be inversely proportional to their initial magnetization. Improvement of magnetic properties of annealed samples may be caused by magnetic cluster formation and pinning effect.     

Magnetism of Fe,Co, and Ni nanowires encapsulated in carbon nanotubes

We have investigated the electronic and magnetic properties of Fe, Co, and Ni nanowires encapsulated in carbon nanotubes (CNTs) using spin polarized ab initio calculation. The incorporated systems with hollow region between the nanowire and the C shell have the enhanced magnetic moments compared to the ferromagnetic nanowires tightly wrapped by CNTs. The Co nanowire encapsulated in CNTs is a strong ferromagnet and has high spin polarization regardless of the distance between the nanowire and the C shell. The results show that the Co-filled CNTs are useful for spin polarized transport nanodevice.     

Autocatalytic redox fabrication and magnetic studies of Co-Ni-P alloy nanowire arrays

Uniform and large-scale Co-Ni-P alloy nanowire arrays have been fabricated by autocatalytic redox reaction in an anodic alumina membrane (AAM). The images of Co-Ni-P alloy nanowire arrays and single nanowires are obtained by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the nanowires. The results indicate that the Co-Ni-P nanowire arrays are amorphous in structure. The magnetic property of Co-Ni-P nanowire arrays is characterized using a vibrating sample magnetometer (VSM). The hysteresis loops show that the easily magnetized direction of Co-Ni-P nanowire arrays is parallel to the nanowire arrays and that it has obvious magnetic anisotropy as a result of the shape anisotropy.     

Electroless synthesis of large scale Co-Zn-P nanowire arrays and the magnetic behaviour

Co-Zn-P nanowire arrays have been synthesized by electroless deposition in an anodic alumina membrane (AAM). The images of Co-Zn-P nanowire arrays and single nanowires are obtained by both scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the nanowires. The results indicate that Co-Zn-P nanowire arrays are amorphous in structure. The hysteresis loops characterized by a vibrating sample magnetometer (VSM) show that the easily magnetized direction of Co-Zn-P nanowire arrays is parallel to the nanowire arrays and that there exhibits clearly a magnetic anisotropy as a result of the shape anisotropy.     

Hyperfine Interaction Studies on Y, Zr, Nb, Mo, Rh, In and Xe in Co

Nuclear magnetic resonance on oriented nuclei and modulated adiabatic fast passage on oriented nuclei measurements were performed on several 4d and 5sp impurities in polycrystalline Co(fcc) foils and Co(hcp) single crystals. The hyperfine fields of Y and Zr in Co(fcc), the hyperfine fields of Y, Zr, Nb, Mo, Rh, In and Xe in Co(hcp), the electric field gradients of Zr, Nb and In in Co(hcp), and the nuclear spin-lattice relaxations of Zr, Nb, Rh and In in Co(hcp) were determined. The dependence of the hyperfine fields and electric field gradients in Co(hcp) on the angle between the magnetization and the c axis was investigated in most cases. The magnetic-field dependence of the spin-lattice relaxation was studied for Nb, Rh and In in Co(hcp), applying the magnetic field perpendicular to the c axis. The known hyperfine interaction parameters of the 4d and 5sp impurities in Co(fcc) and Co(hcp) are summarized. The new results provide a more detailed picture of the hyperfine interaction in Co.     

Nanowire manipulation on surfaces through electrostatic self‐assembly and magnetic interactions

A method for fabricating aligned nanowire arrays on surfaces is shown. Gold and segmented Au/Ni/Au nanowires of high aspect ratio have been prepared by template electrosynthesis, and functionalized with charged short alkanethiols that can be ionized in aqueous solutions. Different distributions of funtionalized nanowires could be obtained on large surfaces from nanowire aqueous suspensions, avoiding aggregation due to electrical repulsion. Due to the high magnetic anisotropy of segmented Au/Ni/Au nanowires chaining of aligned nanowires could be obtained by applying a low magnetic field. While electrostatics favours side wire interactions due to the high aspect ratio, concurrent electrostatics and applied magnetic field yields end‐to‐end interaction and linear alignment without bifunctionalization. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

[110]Au纳米线在加温过程中结构与热稳定性的原子级模拟研究

采用分子动力学方法结合量子修正Sutton-Chen型多体力场,对[110]Au纳米线在升温过程中的结构与热稳定性进行了研究,并引入Lindemann指数和最小半径来研究它的熔化机理和形状演化.结果表明:纳米线在预熔之前,局部区域发生了由fcc到hcp的结构转变.纳米线的预熔首先出现表面上,然后向内部传播,最后才完全熔化为液态结构.纳米线在完全熔化后才开始出现径缩,并最终断裂成为球形纳米团簇.     

FeCo二元合金纳米线阵列的磁化反转

利用交流电化学沉积方法在氧化铝模板中制备了一维结构的Fe_xCo_1-x(0 ≤ x ≤ 0.51)二元合金纳米线阵列.X射线衍射结果显示,单质Co纳米线为(100)择优取向的hcp结构,FeCo合金纳米线则呈现(110)择优取向的bcc结构,而且衍射峰随纳米线中Fe含量的增加向低角度偏移.室温磁性测量结果显示, FeCo合金纳米线具有较好的磁特性.与Co纳米线相比,Fe的引入改善了Co纳米线的磁性能,使其呈现出较大的矫顽力和较高的矩形比.采用一致转动模型和对称扇形机理的球链模型分别计算了FeCo合金纳米线的矫顽力, 发现其磁化反转机理与对称扇形机理的球链模型相符合.     

Magnetic properties of amorphous β-FeOOH nanowire arrays

β-FeOOH nanowire arrays with diameters of 50–200 nm have been fabricated by electrochemical deposition using two-step anodic porous alumina templates. The as-prepared nanowires are homogeneous and have large aspect ratios. The selected area electron diffraction photo performed on a single wire was used to confirm the amorphous crystal structure further. The magnetic properties of these nanowire arrays were firstly investigated by using a SQUID magnetometry. The ZFC and FC studies show that these nanowire arrays exhibit spin-freezing phenomena at low temperature. The temperature-dependent magnetization curves show that the Neel transition temperatures are much lower than that of bulk material. Moreover, hysteresis was found at 5 K and the coercivities up to about 1500 Oe. The size-dependent magnetic properties were also investigated. These abnormal magnetic behaviours can be interpreted in terms of the amorphous crystal structure and the low dimensionality of the nanowire arrays.     

Fabrication and magnetic properties of ordered 20 nm Co-Pb nanowire arrays

Ordered Co-Pb nanowire arrays embedded in anodic alumina template were successfully fabricated by electrodeposition. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) observations revealed that the Co-Pb nanowires were polycrystalline with uniform diameters around 20 nm and lengths up to several micrometers. Magnetic measurements showed that the coercivity and remanence of the as-deposited Co-Pb nanowires decreased with the increase of the Pb content. After annealing the Co-Pb nanowires present higher coercivities (2.4-2.5 kOe) than that of pure Co nanowires (2.1 kOe) and the dependence of coercivity and remanence on the Pb content is inconspicuous. A phase separation of Co and Pb occurred after annealing. The familiar pinning model was employed to explain the above experimental results.     

The effect of structure on magnetic properties of Co nanowire arrays

Co nanowire arrays with three typical diameters of 20, 50 and 120 nm have been fabricated into anodic alumina oxide templates using an ac electrodeposition method. It is found that the crystal texture of the Co nanowires depends on the pH value of the deposition electrolyte. X-ray diffraction results show that the (1 0 0) texture appears at pH 6.2, while the diffraction peaks of (1 0 0) and (1 0 1) appear at pH 6.4 with the diameter of 20 nm. In addition, the (0 0 2), (1 0 0) and (1 0 1) peaks appear with an increase of pH value for the nanowire arrays with diameters of 50 and 120 nm, respectively. Magnetic measurements indicate the effect of structure on the magnetic properties of the nanowire arrays, which depend strongly on the different diffraction peaks, as adjusted by the pH value.