Magnetic Properties Of Ni Nanowires Research Articles

Magnetic Properties of Ni Nanowires in Porous Anodic Alumina Matrix

Magnetic Properties of Ni Nanowires in Porous Anodic Alumina Matrix

Robustness of the enhanced magnetic anisotropy in Ni nanowires regardless of the deposition potential

The effects of the deposition potential on the structural and magnetic properties of Ni nanowires with a diameter of 40 nm and lengths varying from 16 up to 56 μm have been studied. The results show that very long NWs exhibit a large enhancement of their uniaxial magnetic anisotropy. This anisotropy reaches values as high as 1.6 × 106 erg/cm3 that is comparable with the value due to the magnetostatic anisotropy contribution (≈ 5 × 106 erg/cm3) and as shown from the results this large anisotropy is practically insensitive to the deposition potential. Moreover, as shown on shorter NWs, this enhancement of the anisotropy is not observed and interestingly the potential does induce structural changes that relate to their magnetic properties. The enhanced anisotropy observed in long NWs is a robust effect as it is independent of the potential, making this property attractive for applications where high uniaxial anisotropies are required.

Effect of morphology and ageing on the magnetic properties of nickel nanowires

The growth of low dimensional magnetic nanostructures can create exciting properties which show a significant difference when compared to their bulk counterparts. The present work reports the effect of temperature and ageing on the magnetic properties of Ni nanowires. The synthesis of polycrystalline Ni nanostructures with different controllable morphologies was accomplished by a facile wet-chemical reduction route, disregarding hydrothermal conditions, magnetic fields or templates. Reaction pH is found to be critical in determining the morphology. Magnetic dipolar interactions drive sea-urchin-like nanoparticles to self-assemble, forming hierarchical nanowire structures that are analogous to the stem of the Euphorbia plant. The impact of morphology and temperature change on the magnetic properties is deeply investigated. Finally, the effect of ageing up to twelve months on the chemically derived nickel nanowire’s magnetic properties are investigated.

Structural and magnetic properties of Ni nanowires grown in mesoporous silicon templates

Structural and magnetic properties of Ni nanowires electrochemically deposited into pores of mesoporous silicon template under the stationary galvanostatic regime have been investigated. Samples have been exhaustively studied by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and specific magnetization measurements. SEM analysis revealed the formation of porous silicon/nickel nanocomposite at the initial stages of Ni deposition with the characteristic dimension of Ni nanoparticles in the range of 40–60nm. After 60min of deposition Ni continuous nanowires of 10μm length have been formed. XRD analysis confirmed the polycrystalline structure of Ni in the mesoporous silicon template with the preferential orientation along [111] axis. Also some amount of silicide Ni2Si was formed, which diffraction peak at 2Θ≈33° was especially pronounced for low deposition times. The possible mechanism of nickel silicide formation during the electrochemical process has been discussed. It was supposed that, the presence of amorphous silicon on pore walls facilitates the diffusion of Ni inside silicon matrix with subsequent nickel silicide formation without heating. The idea has been confirmed by the fact that on crystalline silicon the formation of nickel silicide was not observed.The magnetic properties have been investigated by studying the temperature dependence (77K–700K) of the specific magnetization σ. The measured σ values were lower with respect to that of bulk Ni. The effect has been explained by the influence of uncontrolled formation of nickel silicide, which causes, after heating, larger irreversibility of σ(T) curves for samples with less deposition time. The obtained σ(T) dependencies allowed us to determine the Curie temperature, TC, which for low deposition times of Ni was lower (575K) with respect to the bulk Ni (630K). This is caused by the influence of dimensional effects on TC value.

High temperature finite-size effects in the magnetic properties of Ni nanowires

The magnetic response of nickel nanowires embedded in porous alumina has been investigated in a wide temperature range, from 5 K up to 700 K. Hysteresis loops and magnetization isotherms were measured on samples of Ni nanowires with different sizes and morphologies up to the Curie temperature. At room temperature, the magnetic response shows evidences of a particle-to-wire crossover above an aspect ratio L/D = 4.3. The magnetic coercivity of high aspect ratio Ni nanowires in the direction parallel to the nanowires has a maximum at T ≈ 400 K, while in the parallel direction Hc decreases continuously with increasing temperature. It is explained in terms of competing anisotropies, magnetocrystalline and magnetoelastic. The expansion of the aluminium support of the membrane plays a fundamental role in the temperature dependence of the coercive field. We find also that TC progressively decreases due to a finite-size effect as the wire's diameter decreases.

Effect of Annealing on the Magnetic Properties of Ni Nanowires Prepared by Using an Anodized Aluminum Oxide Template

Effect of Annealing on the Magnetic Properties of Ni Nanowires Prepared by Using an Anodized Aluminum Oxide Template

Synthesis of Ni nanowires via a hydrazine reduction route in aqueous ethanol solutions assisted by external magnetic fields

Abstract One-dimensional Ni nanostructures were synthesized via a hydrazine reduction route under external magnetic fields. The mixture of de-ionized water and ethanol was used as the reaction solvent and hydrazine hydrate as reducing agents. The morphology and properties of Ni nanostructures were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). It was found that the magnetic field strength, concentration of Ni ions, reaction time and temperature as well as pH values played key roles on formation, microstructures and magnetic properties of Ni nanowires. The optimal wires have diameter of ∼200 nm and length up to ∼200 μm. And their coercivity is ∼260 Oe, which is much larger than the commercial Ni powders of 31 Oe. This work presents a simple, low-cost, environment-friendly and large-scale production approach to fabricate one-dimensional magnetic materials. The resulting materials may have potential applications in conductive filters, magnetic sensors and catalytic agents.

단위 세포당 n(n=1-4)개의 원자를 갖는 Nin나노와이어 계의 구조및 자기적 특성에 대한 제일원리 연구

제일원리적 국소 스핀밀도 근사에 의한 계산방법을 이용하여 Ni 나노와이어에 대한 전자구조와 자기적 성질을 연구하였다. 단위 세포당 Ni 원자의 개수(n = 1 − 4)에 따른 구조적 특성에 따라 각각의 나노와이어에 대한 결합에너지와 자기모멘트를 계산하였다. 계산결과 지그재그-사각형 <TEX>$Ni_4$</TEX> 나노와이어가 에너지적으로 가장 안정하였다. 또한 Ni 나노와이어의 자기모멘트는 선형 나노와이어 Ni1가 <TEX>$1.34 {\mu_B}/atom$</TEX> 로 가장 큰 값을 나타냈으며, 단위 세포당 원자 개수가 증가될수록 자기모멘트는 감소하여 사각형 나노와이어 <TEX>$Ni_4$</TEX>의 자기모멘트가 <TEX>$0.91 {\mu_B}/atom$</TEX> 로 가장 작은 값을 나타냈다. <TEX>$Ni_n$</TEX>(n = 1 − 4)의 각각의 구조들에 대한 상태밀도, 에너지 띠 등의 전자구조 계산결과를 제시하고 논의 검토하였다. The magnetic properties of Ni nanowires consisting of one to four atoms are investigated by mean of ab initio spin-polarized density functional calculations. Stability of zigzag-square <TEX>$Ni_4$</TEX> nanowire is larger than <TEX>$Ni_4$</TEX> nanowires with square. The magnetic moment of linear <TEX>$Ni_1$</TEX> is <TEX>$1.34{\mu_B}/atom$</TEX>, which is the largest magnitude among moments of five Ni nanowires. The magnetic moment of Ninanowires show to be decreased by increasing the number of atoms in unit cell. The smallest moment is <TEX>$0.91 {\mu_B}/atom$</TEX> for square <TEX>$Ni_4$</TEX> nanowire. The spin polarization of zigzag-square <TEX>$Ni_4$</TEX> nanowire is 32% higher than that of fcc bulk Ni.

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 . 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.

Magnetic properties of Ni nanowires in porous alumina arrays

Magnetic properties of Ni nanowires in porous alumina arrays are investigated. Nickel nanowires of various sizes were prepared by electrodepositing into porous alumina arrays. Their magnetization curves were measured from 1.7 to 300 K with a SQUID magnetometer. Variation in the coercive force with temperature shows different behaviour depending on the diameter of porous alumina arrays.

Magnetic properties of Ni nanowires in self-assembled arrays

Magnetic properties of Ni nanowires electrodeposited into self-assembled porous alumina arrays have been investigated. By anodizing aluminum in sulfuric acid and immersing the as-anodized template into phosphoric acid for different lengths of time, we are able to vary the diameters of the subsequently deposited nanowires between 8 and 25 nm. The coercivity measured along wire axis first increases with the wire diameter, reaches a maximum of 950 Oe near a diameter of 18 nm, and then decreases with further increase of wire diameter. The dependence of the magnetization of Ni nanowires is found to follow Bloch's law at low temperature but with the Bloch exponent decreasing from the bulk value and the Bloch constant increasing from the bulk value by an order of magnitude.