High density hexagonal nickel nanowire array

Nielsch, Kornelius; Wehrspohn, Ralf B.; Barthel, J.; Kirschner, J.; Fischer, Saskia F.; Kronmüller, H.; Schweinböck, T.; Weiss, Dieter; Gösele, U.

doi:10.1016/s0304-8853(02)00536-x

Cited by 142 publications

(85 citation statements)

References 17 publications

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“…Although similar MFM studies were recently performed by other groups on different types of samples, most of these involved particles with ͑very͒ much lower aspect ratios. 17,20,23,24 For wires with such high ͑Ͼ60͒ aspect ratios as ours, the above result is certainly nontrivial since the AFM/MFM is only sensitive to the ends of the wires, whereas the SQUID measures the volume magnetization. Thus, the apparent agreement between the two measurements confirms the conclusion already drawn from the Mössbauer spectra that the Fe nanowires are indeed monodomain ferromagnetic needles.…”

Section: Resultsmentioning

confidence: 79%

Magnetization reversal of ferromagnetic nanowires studied by magnetic force microscopy

et al. 2003

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The magnetization reversal of two-dimensional arrays of parallel ferromagnetic Fe nanowires embedded in nanoporous alumina templates has been studied. By combining bulk magnetization measurements ͑supercon-ducting quantum interference device magnetometry͒ with field-dependent magnetic force microscopy ͑MFM͒, we have been able to decompose the macroscopic hysteresis loop in terms of the irreversible magnetic responses of individual nanowires. The latter are found to behave as monodomain ferromagnetic needles, with hysteresis loops displaced ͑asymmetric͒ as a consequence of the strong dipolar interactions between them. The application of field-dependent MFM provides a microscopic method to obtain the hysteresis curve of the array, by simply registering the fraction of up and down magnetized wires as a function of applied field. The observed deviations from the rectangular shape of the macroscopic hysteresis loop of the array can be ascribed to the spatial variation of the dipolar field through the inhomogeneously filled membrane. The system studied proves to be an excellent example of the two-dimensional classical Preisach model, well known from the field of hysteresis modeling and micromagnetism.

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Section: Resultsmentioning

confidence: 79%

Magnetization reversal of ferromagnetic nanowires studied by magnetic force microscopy

et al. 2003

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“…[3±5] Currently, the fabrication of Ni nanowires mainly depends on a template technique that involves electrochemical deposition or metal± organic chemical vapor deposition (CVD) of metals into the nanopores of template materials, such as anodic alumina (AAO) film [3] and carbon nanotubes.…”

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confidence: 99%

Complex‐Surfactant‐Assisted Hydrothermal Route to Ferromagnetic Nickel Nanobelts

et al. 2003

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Nickel is an important ferromagnetic material. Anisotropic magnetic nanoparticles are expected to exhibit interesting magnetic properties.[1] Nickel one-dimensional (1D) nanostructures have thus attracted much attention recently because of their potential applications in magnetic sensors and memory devices.[2] Different Ni 1D nanostructures have been successfully synthesized by various methods. [3±5] Currently, the fabrication of Ni nanowires mainly depends on a template technique that involves electrochemical deposition or metal± organic chemical vapor deposition (CVD) of metals into the nanopores of template materials, such as anodic alumina (AAO) film [3] and carbon nanotubes.[6] However, little work on the preparation of Ni 1D nanostructures in aqueous solution has been reported to date. [7] Such a solution-phase approach may provide a more promising technique for preparing 1D nanostructures than conventional methods in terms of cost and potential for large-scale production.[8] Here we report a complex-surfactant-assisted hydrothermal reduction method to synthesize single-crystal Ni nanobelts with high yield. Ni nanobelts were generated by reducing a Ni II -tartrate complex in alkaline solution and in the presence of a suitable surfactant at relatively low temperature (110 C). These nanobelts had typical widths of 500±1000 nm, a thickness of onlỹ 15 nm, and lengths of up to 50 lm. This new type of nanostructure of a ferromagnetic metal should be explored in physical property studies and for interesting applications as a new kind of nanoblock.Practically, the present approach to the synthesis of Ni nanobelts is similar to the process for electroless Ni plating. [9] In our study, sodium tartrate (Na 2 C 4 H 4 O 6 ) was used as the complexing reagent to form a complex, Ni(C 4 H 2 O 6 ) 2± . The formation of Ni II complex sharply decreased the free Ni 2+ concentration in the solution, which resulted in a relatively slow rate of generation of Ni atoms. A slow reaction rate was favorable for separating the growth step from the nucleation step. For this reason, we selected a high concentration of both tartrate and alkali. Nevertheless, we found that adjusting the concentrations of tartrate and NaOH was not sufficient for the formation of 1D nanostructures. In this case, only spongelike Ni particles were produced. In the solution-phase synthesis of nanocrystals, kinetically controlling the nucleation and growth rate could conceivably modulate the size and shape of the final products.[10] Some recent work has suggested that the shape of the nanocrystals can be effectively modulated by adding chemical capping reagents to the synthetic systems. It is believed that the selective interaction of the capping molecules on a facet of the first-formed nanoparticles is the key to anisotropic growth of nanoparticles. [4,11] In this work, in order to achieve the desired Ni nanobelts, the anion surfactant sodium dodecyl benzenesulfonate (SDBS) was introduced to the synthesis system. We found that SDBS had a remarkable effect o...

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“…Esta interacción dipolar condiciona, en algunos casos, la inversión de la polarización del arreglo [14]. La histéresis magnética de los nanohilos individuales está determinada por la anisotropía magnética efectiva, la que en general resulta de varias contribuciones de distinta naturaleza, como la anisotropía magneto-cristalina, la anisotropía de forma y/o la magneto-elástica.…”

Section: Introductionunclassified

Influencia de la porosidad en las propiedades magnéticas de arreglos de nanohilos de Ni

Meneses

Bercoff

2015

Matéria (Rio J.)

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RESUMENSe estudiaron las propiedades de histéresis magnética de arreglos ordenados de nanohilos de Ni, electrodepositados éstos en una membrana de alúmina con un arreglo hexagonal de poros cilíndricos. Se analizó el efecto de la geometría de los nanohilos individuales (diámetro y longitud) y del ordenamiento y porosidad del arreglo sobre la coercitividad y la remanencia del conjunto. Las membranas de alúmina auto-ensambladas se sintetizaron por anodizado en dos pasos, usando una celda electroquímica y potencial eléctrico constante. Se variaron los diámetros de poro entre 20 nm y 40 nm (no así la distancia media entre ellos) sumergiendo las membranas en ácido fosfórico al 5% durante distintos tiempos. Estas membranas se caracterizaron por microscopía de barrido (SEM). Los nanohilos de Ni se obtuvieron por electrodeposición AC, a 20 V, 200 Hz y temperatura ambiente. Una vez sintetizados, los arreglos de nanohilos se caracterizaron estructuralmente por SEM y magnéticamente usando un SQUID. Se observa que las propiedades magnéticas de los arreglos son fuertemente dependientes de la relación largo/diámetro de los nanohilos, la que regula el valor de su anisotropía de forma, y también de la porosidad, que determina la magnitud del campo de interacción dipolar que percibe cada nanohilo por la presencia de sus vecinos en el arreglo. En particular, se encontró que la coercitividad decrece con la porosidad y que el parámetro ε, que regula la intensidad de las barreras de energía del sistema, debe ser variable y depender de la porosidad del arreglo para ajustar bien los datos experimentales. Palabras clave: Nanohilos, Propiedades magnéticas, Níquel ABSTRACTThe hysteresis properties of ordered arrays of Ni nanowires, electrodeposited into cylindrical nanoporous alumina membranes were investigated. The effect of the nanowire geometry (diameter and length), the array order and the nanowires' volume fraction on the array coercivity and remanence were analyzed. Porous alumina membranes were produced by a two-step anodization process in a potentiostatic electrochemical cell. The pores' diameters were varied from 20 nm to 40 nm by immersing the membranes in a 5% phosphoric acid solution for different times. The membranes were characterized using a scanning electron microscope (SEM) and both the pore size distribution as well as their separation were determined. These membranes were used as templates for the AC electrodeposition of Ni nanowires, using a voltage of 20 V and a frequency of 200 Hz, at room temperature. The Ni nanowire arrays were structurally and magnetically characterized by SEM and with a SQUID magnetometer, respectively, at room temperature. It was found that the magnetic properties of the array strongly depend on the nanowires aspect ratio -length/diameter ratio-which regulates the wire shape anisotropy and also on the porosity, which determines the magnitude of the dipolar interaction field acting on the array. Particulary, it was found that coercitivity decreases with porosity and that the parameter ε, which is...

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High density hexagonal nickel nanowire array

Cited by 142 publications

References 17 publications

Magnetization reversal of ferromagnetic nanowires studied by magnetic force microscopy

Magnetization reversal of ferromagnetic nanowires studied by magnetic force microscopy

Complex‐Surfactant‐Assisted Hydrothermal Route to Ferromagnetic Nickel Nanobelts

Influencia de la porosidad en las propiedades magnéticas de arreglos de nanohilos de Ni

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