Skyrmion motion induced by spin-waves on magnetic nanotubes

We investigate the skyrmion motion driven by spin waves on magnetic nanotubes through micromagnetic simulations.Our key results include demonstrating the stability and enhanced mobility of skyrmions on the edgeless nanotube geometry,which prevents destruction at boundaries—a common issue in planar geometries.We explore the influence of the damping coefficient,amplitude,and frequency of microwaves on skyrmion dynamics,revealing a non-uniform velocity profile characterized by acceleration and deceleration phases.Our results show that the skyrmion Hall effect is significantly modulated on nanotubes compared to planar models,with specific dependencies on the spin-wave parameters.These findings provide insights into skyrmion manipulation for spintronic applications,highlighting the potential for high-speed and efficient information transport in magnonic devices.

Domain wall dynamics in magnetic nanotubes driven by an external magnetic field

We use the Landau-Lifshitz-Gilbert equation to investigate field-driven domain wall propagation in magnetic nan- otubes. We find that the distortion is maximum as the time becomes infinite and the exact rigid-body solutions are obtained analytically. We also find that the velocity increases with increasing the ratio of inner radius and outer radius. That is to say, we can accelerate domain wall motion not only by increasing the magnetic field, but also by reducing the thickness of the nanotubes.

Fabrication and electromagnetic wave absorption properties of amorphous Ni-P nanotubes

Amorphous Ni-P nanotubes are fabricated through electroless chemical deposition inside an anodic aluminum oxide template. The hysteresis loops of Ni-P nanotube arrays are each found to exhibit an unusual isotropic behaviour, which is believed to be due to the competition results between the shape anisotropy and the magnetostatic interaction among nanotubes. The dynamic dependence of permittivity on the frequency spectrum is fitted to the Lorentzian-type dispersion law. The permeability dispersion behaviours have been fitted based on the Kittel equation. Electromagnetic wave absorption properties of Ni-P nanotubes/paraffin composites with different values of thickness （t） are clearly shown by a three-dimensional graph. Furthermore, the bandwidths of composites with different ＂t＂ values can be well presented by a two-dimensional contour graph, which is a novel presentation form. The results show that the composites each have a good microwave absorption performance with t larger than 5.5 mm and with the frequency around 8 gigahertz.

Adsorption of Cr(Ⅵ) in wastewater using magnetic multi-wall carbon nanotubes

Magnetic multi-wall carbon nanotubes were prepared with wet chemical treatments and characterized by a transmission electron microscope （TEM） and X-ray diffraction （XRD）. They were used as adsorbents for the removal of Cr（VI） in aqueous solutions. The effects of adsorbent dosage, the concentration of Cr（VI） in aqueous solution, temperature, and pH value on the removal efficiency were studied. Results showed that the adsorption capacity of the magnetic multi-wall carbon nanotubes increased with the initial Cr（VI） concentration, but decreased with the increase of adsorbent dosage. The adsorption amount increased with contact time. The adsorption kinetics were best represented by the pseudo second-order kinetic model, and the adsorption isotherms indicated that the Langmuir model better reflected the adsorption process. The ob- tained calculation results for the Gibbs free energy revealed that the adsorption was a spontaneous and endothermic process. The enthalpy deviation was 3.835 kJ.mol 1. The magnetic multi-wall carbon nanotubes showed significant potential for application in adsorption of heavy metal ions.

Laccase biosensor using magnetic multiwalled carbon nanotubes and chitosan/silica hybrid membrane modified magnetic carbon paste electrode

A simple and rapid strategy to construct laccase biosensor for determination of catechol was investigated. Magnetic multiwalled carbon nanotubes (MMCNT) which possess excellent capability of electron transfer were prepared by chemical coprecipitation method. Scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) were used to identify its surfacetopography and magnetization, respectively. Laccase was immobilized on the MMCNT modified magnetic carbon paste electrode by the aid of chitosan/silica (CS) hybrid membrane. Using current-time detection method, the biosensor shows a linear response related to the concentration of catechol in the range from 10-7 to 0.165×10-3 mol/L. The corresponding detection limit is 3.34×10-8 mol/L based on signal-to-noise ratios (S/N) ≥3 under the optimized conditions. In addition, its response current retains 90% of the original after being stored for 45 d. The results indicate that this proposed strategy can be expected to develop other enzyme-based biosensors.

Splitting Phenomenon Induced by Magnetic Field in Metallic Carbon Nanotubes

In the framework of the tight-binding model, the excitons states and linear absorption spectra are calculated in the metallic single-walled carbon nanotubes, with the axial magnetic field applied. From our calculations, it is found that for the Mll and M22 transitions, the exeiton states are split into four separate column states by the applied magnetic field due to the symmetry breaking. More interesting is that the splitting can be directly reflected from the linear absorption spectra~ which are dominated by four main absorption peaks. In addition, the splitting with increasing the axial magnetic field is also calculated, which increases linearly with the applied magnetic field. The obtained results are expected to be detected by the future experiments.

Combined Effect of Uniaxial Strain and Magnetic Field on the Exciton States in Semiconducting Single-Walled Carbon Nanotubes

The exciton states of semiconducting carbon nanotubes are calculated by a tight-binding model supplemented by Coulomb interactions under the combined effect of uniaxial strain and magnetic field. It is found that the excitation energies and absorption spectra of zigzag tubes（11,0） and（10,0） show opposite trends with the strain under the action of the magnetic field. For the（11,0） tube, the excitation energy decreases with the increasing uniaxial strain, with a splitting appearing in the absorption spectra. For the（10,0） tube, the variation trend firstly increases and then decreases, with a reversal point appearing in the absorption spectra. More interesting,at the reversal point the intensity of optical absorption is the largest because of the degeneracy of the two bands nearest to the Fermi Level, which is expected to be observed in the future experiment. The similar variation trend is also exhibited in the binding energy for the two kinds of semiconducting tubes.

Magnetic Transport Properties of Fe-Phthalocyanine Dimer with Carbon Nanotube Electrodes

Based on the non-equilibrium Green＇s method and density functional theory, the magnetic transport of Fe- phthMocyanine dimers with two armchair single-wailed carbon nanotube electrodes is investigated. The results show that the system can present high-performance spin filtering, magnetoresistance, and low-bias spin negative differential resistance effects by tuning the external magnetic field. These results show that the Fe-phthalocyanine dimer has the potential to design future molecular spintronic devices.

Cd(Ⅱ)removal from amino acids-bearing wastewater:Critical evaluation and comparison of using magnetic carbon nanotubes vs.magnetite

In the present work,two magnetic adsorbents(magnetic carbon nanotunes“MCNT”and magnetite“Mag”)were tested for cadmium“Cd(Ⅱ)”removal from water in the presence of various amino acids“AA”(aspartic acid,glutamic acid“Glu”,glycine and cysteine).MCNT was prepared by initially oxidizing carbon nanotubes(CNT)by three different methods:nitric acid method,ammonium persulphate method,Hummer's method.Magnetite was then deposited on the oxidized CNT to produce the corresponding magnetic carbon nanotube adsorbents:NA-MCNT,APS-MCNT,HUM-MCNT,respectively.Adsorption of Cd(Ⅱ)on various MCNT was investigated in the presence/absence of AA where various factors were studied:pH,oxidation method of CNT,type of AA,magnetite-to-CNT ratio.It was found that the presence of AA significantly reduced the adsorption capacity of MCNT towards Cd(Ⅱ)at all pHs(reduction occurred from 49.8 mg g^(-1)to 12.5 mg g^(-1)).Contrary adsorption capacity of Cd(Ⅱ)on bare magnetite“Mag”was noticeably enhanced in the presence of AA(for Glu,enhancement occurred from 6.9 to 22.3 mg g^(-1)).Due to cheapness of Mag relative to CNT,it was recommended to use Mag rather than MCNT for Cd(Ⅱ)removal from AA-bearing water.So that the optimum uptake method was proposed using Mag at pH 8 in the presence of Glu at concentration ratio(1:3 Cd(Ⅱ):Glu).Mag was selective towards Cd(Ⅱ)even in the presence of co-existing ions.The use of Mag for five cycles decreased adsorption efficiency to 80%which indicated that adsorption system was cost effective.Real water samples gave higher adsorption of Cd(Ⅱ)in the presence of Glu than in distilled water.As a conclusion,it was recommended to use Mag rather than MCNT for Cd(Ⅱ)removal in the presence of AA.

Cd(Ⅱ)removal from phenols-bearing wastewater using magnetic carbon nanotubes

This project studied Cd(Ⅱ)uptake from phenols-bearing wastewater using magnetic carbon nanotubes(MCNT)as adsorbent.Initially,Cd(Ⅱ)complexation with various phenols was confirmed by FT-IR spectroscopy.Factors affecting Cd removal are:solution pH;type of phenol[phenol(Ph),2-chlorophenol(2-CP),2-nitrophenol(2-NP),and 2,4-dinitrophenol(2,4-DNP)];Mag:CNT mass ratio;Cd:phenolic compound molar ratio;and the effect of order of adding adsorption components(MCNT,Cd(Ⅱ),phenolic compound)to the extraction medium.It was found that the presence of phenols in the extraction medium caused a 10e50%decrease in Cd(Ⅱ)uptake.This was probably due to a competition between phenols/surface functional groups towards Cd(Ⅱ);or phenols/Cd(Ⅱ)to occupy the surface functional groups.2,4-DNP was selected as a model phenolic compound.The optimum adsorption conditions[1:1 M ratio of(Cd(Ⅱ):2,4-DNP)at pH 6 using MCNT(1:1)adsorbent]resulted in adsorption capacity of 17.9 mg Cd g^(-1).The best order of adding reagents was(Cd(Ⅱ)þMCNT(1:1))and then 2,4-DNP.The regeneration of the adsorbent was possible by using 0.5 M HNO_(3)where 90%of adsorption efficiency was reserved after three times of successive use.Upon presence of co-existing ions,75%of the adsorption efficiency was maintained.The applicability of the proposed adsorption method on real water samples was evaluated.

Controllable nucleation and deformation of skyrmions on surface of magnetic nanotubular monolayer

Magnetic skyrmions emerge when the energy of ferromagnetic exchange interaction promoting parallel alignment of spins enters in competition with energies favoring non-collinear alignment of spins such as Dzy aloshinskii-Moriya interaction(DMI),long-rang dipole-dipole interaction(DDI),or higher-order exchange interactions.We perform an unbiased Monte Carlo simulation to study the DMI-based skyrmion nucleation and stabilization on the surface of magnetic nanotubular monolayer controlled by tuning constants of DDI(g) and next-nearest-neighbor antiferromagnetic exchange interaction(j') with appropriate balance.Without g and j',the loosely distributed skyrmions initially nucleate on the surface of nanotube approaching to the magnetic field(h) direction with increasing h in the intermediate range.Then,the skyrmion size,shape,density,distribution and crystal structure,as well as its driven field range,are tailored by g and j'.This work demonstrates the skyrmion nucleation mechanisms in three-dimensional magnetic nanostructures with curvature effect and multiple interactions,serving as a benchmark for a guide to experimentalists for preparation of samples in magnetic skyrmion states.