Magnetic Properties Of Nanowires Research Articles

Enhancing Electronic and Magnetic Properties in Eu‐Doped GaN Nanowires via p‐f Hybridization of Eu‐Defect Complexes

AbstractDensity functional theory (DFT) is employed based on the generalized gradient approximation (GGA), including the Hubbard (U) parameter, to investigate the modification of the electronic properties of GaN nanowires (NWs) by Eu dopants introduced via Eu‐associated defect complexes to explore the origin of magnetic characteristics. These findings show that incorporating Eu dopants, including Eu‐intrinsic defect complexes, in GaN NWs leads to a significant change in the electronic properties of GaN, as evident from p‐f state hybridization, resulting in unique magnetic characteristics. However, while Ga‐vacancies (VGa) in Eu‐doped GaN NWs impart a significant magnetic moment on N atoms, N‐vacancies (VN) produce a negligible effect on the magnetic properties of NWs. To predict the magnetic exchange effect, two Eu3+ ions are introduced in the NWs, showing that the complex with two Eu atoms and Ga‐vacancy (2Eu‐VGa) induces stable ferromagnetism above room temperature.

Laccase‐based amperometric biosensor enhanced by Ni/Au/PPy‐COOH multisegmental nanowires for selective dopamine detection

AbstractOne‐dimensional Ni/Au/PPy‐COOH nanowires with multiple segments were synthesized in this study. Smooth surfaces and magnetic properties of nanowires were investigated by scanning transmission electron microscopy (SEM), Energy‐dispersive X‐ray spectroscopy (EDX), and Electron Spin Resonance (ESR) techniques. The nanowires were used to modify the screen‐printed electrode surface and as a micro‐environment for Trametes versicolor laccase. The ability of this enzyme biosensor to detect dopamine change in human biological samples was demonstrated by a wide linear range (0.01–50 μM) and a low LOD (2.265 nM). In addition, the biosensor exhibited excellent selectivity allowing the detection of dopamine in the presence of ascorbic acid, uric acid, L‐Cys, serotonin, and glucose, with high sensitivity of reduction currents obtained at −0.2 V (vs. Ag/AgCl). The proposed biosensor allowed the detection of dopamine in commercial serum and artificial urine with recovery values close to 100 %. It also demonstrated reproducibility, reusability, and long‐term storage stability. The sensitivity, Kmapp, and Imax values of the biosensor were determined as 2.05 μM and 1.03 μA, respectively. The LAC‐Ni/Au/PPy‐COOH/NAF/SPE biosensor is a reliable design for detecting dopamine with a wide linear range.

Effect of composition, electrolyte pH, annealing temperature and electrodeposition waveform on the magnetic properties of Co-Cu nanowire alloys

Arrays of Co0.2Cux, with 0<x<0.1, nanowires (NWs) have been synthesized. CoCu NWs have been grown into the AAO templates by ac electrodeposition. The anodic aluminum oxide template (AAO) were synthesized by a two-step anodization process of pure Al foils in sulfuric acid. The effect of small addition of Cu to Co NWs by varying the concentrations of Cu+2 ions in the electrolyte, as well as the effect of annealing on the magnetic properties of NWs was investigated. Eventually, the effect of changing waveforms applied to nanowire deposition was studied. The results showed that the coercivity of cobalt NWs decreased by adding copper impurity as a non-magnetic material from 1337 Oe to 660 Oe. By annealing of the alloy NWs up to 450 °C, the coercivity increases from 1140 Oe value for pure Co NWs up to 1541 Oe for CoCu NWs due to the removal of structural stresses of the nanowire.

Coupled electrodeposition and magnetic properties of ternary CoFeW alloys

The iron (Fe) cobalt (Co) tungsten (W) alloys exhibit unique combinations of mechanical and soft magnetic properties, good corrosion and wear resistance, and biocompatibility, which makes them desirable candidate for numerous practical applications. A nano-porous alumina template with electrodeposited FeCoW alloy nanowires (NWs) is a polycrystalline material with the grain size was about ~1 − 3 nm. Here, we first time report the composition dependent structural, and magnetic properties of FeCoW NWs embedded in ~25 nm anodic alumina (AAO) template by electrodeposition. By keeping the W concentration same, and decreasing the concentration of Co2+ and Fe2+ ions in the solution, 2–3% to 8–9% W content was increased. The EDX and XPS analysis confirms the co-deposition of W ions along with Fe and Co ions. The magnetization curves showed that 2–3% At. % of W in CoFe NWs significantly increases the saturation magnetization of NWs. Therefore, FeCoW alloy with low W content could be targeted for the design of recording components and shape memory devices in future. Deposition potential also has a notable effect on the final composition, structure and magnetic properties of NWs.

Synthesis, Structure and Magnetic Properties of Nanowires Made from Alloys of Iron-Group Metals

Synthesis, Structure and Magnetic Properties of Nanowires Made from Alloys of Iron-Group Metals

Non-Aqueous electro-deposition of novel one-dimensional Sm2Co17 nanostructures and magnetic field annealing effect on structural and magnetic properties

Through a versatile and quite economical technique of DC electro-deposition, Sm2Co17 nanowires (NWs) have been fabricated into the nanochannels of anodic aluminum oxide (AAO) templates by using non-aqueous electrolyte. The average diameter and length of NWs are 80 nm and 3 µm respectively. The structural and magnetic properties of NWs have been investigated before and after magnetic field (MF) annealing with magnetic field strength of 1 T applied parallel to the NWs axis at temperature of 300 °C. SEM and TEM have been employed to observe the morphology of NWs after partial and full etching respectively. Deposition of SmCo alloy has been confirmed through EDX analysis whereas XRD peaks shows hexagonal closed packed (hcp-P63/mmc) as the dominant phase with (203) preferred orientation. After MF annealing the crystallinity got improved as manifested by the increase in peak sharpness. Furthermore, after the said field assisted heat treatment the magnetic parameters including coercivity (Hc) from 91 to 527 Oe for θ = 0°, from 101 to 151 Oe for θ = 90° and squareness (SQ) from 0.040 to 0.16 for θ = 0°, from 0.037 to 0.032 for θ = 90° have been observed through VSM. A switching of magnetization reversal mechanism from curling to coherent rotation has been observed after MF annealing due to the stronger inter-wire coupling which leads to parallel alignment of magnetic moments of adjacent NWs. Temperature dependent study has been carried out employing PPMS manifesting gradual increase in Hc from 67 to 440 Oe, Ms from 5.4 × 10−3 to 6.1 × 10−3 emu and SQ from 0.19 to 0.25 with the decrease in temperature up to 5 K.

Fabrication, structural and magnetic properties of one-dimensional anti-ferromagnetic FeMn nanostructures

FeMn nanowires have been synthesized by employing DC electro-deposition technique provided with constant stirring during the growth. The use of anodic aluminum oxide (AAO) templates made it possible to get well aligned nanowires with average diameter around 100 nm. Magnetic field annealing with field strength of 1 T applied at angle 0° and 90° to nanowires axis at different annealing temperatures has been employed to study the variation in structural and magnetic properties of nanowires. XRD analysis shows poor crystallinity of as-synthesized arrays but cubic structure with (110) preferred orientation has been resulted after the annealing process. Furthermore, vibrating sample magnetometer (VSM) has been employed to study the saturation magnetization (Ms), squareness ratio (SQ=Mr/Ms) and coercivity (Hc) of the as-synthesized and annealed samples. The as deposited and annealed NWs arrays show the coherent rotation for magnetization reversal process.

Magnetization reversal switching in nanocylinders using dynamic techniques

The high aspect ratio Ni nanocylinders (nanowires and nanotubes) were fabricated by means of potentiostatic electrochemical deposition in porous anodic alumina templates with pore diameter of 200 nm and a thickness of 60 µm. The growth of nanocylinders was found to depend upon deposition parameters. The structural, morphological and magnetic analysis revealed the face-centred cubic texture, uniformity and magnetic properties of nanowires and nanotubes respectively. The dynamic properties of one-dimensional uniform arrays of Ni nanowires (NWs) and nanotubes (NTs) were studied by ferromagnetic resonance technique at various frequencies ranging from 6 to 25 GHz. In particular, we identify the onset of magnetization reversal from the angular variation studies of resonance fields [Hr(θH)] and FMR linewidths [ΔHr(θH)]. Parameters such as gyromagnetic ratio (γ), damping constant (α) and effective field (Heff) were derived from theoretical fits to Hr and ΔHr data. We found that Hr and ΔHr both depend sensitively on the angle between the magnetization direction and wire-axis. For a NT geometry, the fitting of ΔHr(θH) data divulges that the magnetization reversal mechanism dominant by coherent rotation and thereafter beyond transition angle (∼80°) curling mode contributes. In case of nanowires, the curling reversal mode is the dominant magnetization reversal process.

Study of NiCu multilayer magnetic nanowires

Magnetic nanowires play an important role both in basic research, since they can exhibit new physical phenomena, and technological applications, such magnetic sotrage and magnetic sensors. It was investigated the magnetic properties of magnetic nanowires composed of multilayers made of Ni and Cu, fabricated by electrodeposition method in alumina porous template. We obtained their magnetization curves at 2 K and 300 K, and it was intended to perform magnetoresistance measurements. The latter was not done, because it was encountered difficulties in trapping the nanowires between electrodes.

Magnetic properties of nanowires with ferromagnetic core and antiferromagnetic shell

We present a Monte Carlo study of the magnetic properties of thin cylindrical nanowires composed of a ferromagnetic core and an antiferromagnetic shell implementing a classical spin Hamiltonian. We address systematically the impact of interface exchange coupling on the loop characteristics and the magnetization reversal mechanism. We study the effect of shell polycrystallinity on the characteristic fields of the isothermal hysteresis loop (coercivity, exchange-bias). We demonstrate that coupling to a polycrystalline antiferromagnetic shell increases the critical core diameter for transition from transverse to vortex domain walls.

Matrix Synthesis, Structure and Properties of Magnetic Nanowires

Magnetic nanowires (NWs) of pure Fe,Co, Ni, alloys FeCo, FeNi and layered Ni/Cu were obtained by galvanic deposition into the pores of track membranes. The process of deposition was investigated and non-linear character was found. The obtained ensembles of NWs were tested by SEM, TEM, X-ray, Magnetometry and Mässbayer spectroscopy. Element concentration in NWs is differ from concentration of electrolyte and change slightly along the NW length (for alloys). For layer NWs the layers thickness and composition was determined. Different phases in alloys were found. Magnetometry measurements confirmed the magneto-hard properties of FeCo NWs and soft magnetic properties of FeNi NWs. It was also shown that increase of grooving voltage leads to increase of magneto-hard properties due to formation of microcrystalline structure.

Magnetic characterization of cobalt nanowires and square nanorings fabricated by focused electron beam induced deposition.

The magnetic properties of nanowires (NWs) and square nanorings, which were deposited by focused electron beam induced deposition (FEBID) of a Co carbonyl precursor, are studied using off-axis electron holography (EH), Lorentz transmission electron microscopy (L-TEM) and magnetic force microscopy (MFM). EH shows that NWs deposited using beam energies of 5 and 15 keV have the characteristics of magnetic dipoles, with larger magnetic moments observed for NWs deposited at lower energy. L-TEM is used to image magnetic domain walls in NWs and nanorings and their motion as a function of applied magnetic field. The NWs are found to have almost square hysteresis loops, with coercivities of ca. 10 mT. The nanorings show two different magnetization states: for low values of the applied in-plane field (0.02 T) a horseshoe state is observed using L-TEM, while for higher values of the applied in-plane field (0.3 T) an onion state is observed at remanence using L-TEM and MFM. Our results confirm the suitability of FEBID for nanofabrication of magnetic structures and demonstrate the versatility of TEM techniques for the study and manipulation of magnetic domain walls in nanostructures.

Fabrication and magnetic properties of Sm-Co/Fe-Co and Sm-Co/Fe-Co-Dy magnetic nanowires

The Sm-Co/Fe-Co and Sm-Co/Fe-Co-Dy nanowire arrays with smaller diameter are prepared by electrochemical deposition on the anodic aluminum oxide (AAO) templates in this paper. The crystal structure and magnetic properties of nanowires are characterized and analyzed. It is found that the Sm-Co nanowires change from amorphous phase to nanocrystalline state with hard magnetic characterization through annealing at 660 °C for 3 h. In this experiment, rare earth element Dy is added to the Fe-Co solution, and the three alloy nanowires are prepared and researched for the first time. The addition of Dy element produces a new Fe23Dy6 phase in the nanowires. The magnetic hysteresis loops illustrate that the magnetic properties of as-deposited nanowires is improved dramatically after heat treatment and the direction parallel to the nanowire arrays is the easy direction of magnetization which leads to nanowires possessing obvious shape anisotropy. The effect of different Dy ion concentration on nanowires' magnetic properties is investigated in this paper.

Fabrication and magnetic properties of ordered Co100−xPbxnanowire arrays electrodeposited in AAO templates: Effects of annealing temperature and frequency

Abstract

Shape anisotropy and hybridization enhanced magnetization in nanowires of Fe/MgO/Fe encapsulated in carbon nanotubes

Arrays of tunneling magnetoresistance (TMR) nanowires were synthesized for the first time by filling Fe/MgO/Fe inside vertically grown and substrate supported carbon nanotubes. The magnetic properties of nanowires and planar nanoscale thin films of Fe/MgO/Fe showed several similarities, such as two-fold magnetic symmetry and ratio of orbital moment to spin moment. Nanowires of Fe/MgO/Fe showed higher saturation magnetization by a factor of 2.7 compared to planar thin films of Fe/MgO/Fe at 1.5kOe. The enhanced magnetic properties likely resulted from shape anisotropy of the nanowires and as well as the hybridization that occur between the π- electronic states of carbon and 3d-bands of the Fe-surface.

Synthesis, phase composition, and magnetic properties of iron nanowires prepared in the pores of polymer track-etched membranes

Arrays of iron nanowires prepared by the method of galvanic filling of polymer track-etched membrane pores (matrix synthesis) under different electrolysis modes and electrolyte temperatures have been studied. The conditions of the synthesis have been analyzed. The optimal composition and electrolyte temperature have been found. The phase composition and magnetic properties of nanowires have been studied using the methods of electron microscopy, X-ray diffraction, elemental energy-dispersive microanalysis, and Mossbauer spectroscopy. The average nanowire diameter is 100–200 nm. The length varies from 6 to 10 μm. The surface density is ∼108 cm−2 at the average distance to each other of about 1 μm. It has been established that the basis of nanowires is formed by the metal iron nanocomposite that manifests the magnetic properties of bulk α-Fe. It has been found that the preferred orientation of the magnetization inside the iron nanowires arises for an array prepared at a potential of −750 mV.

Phase dependent magnetic properties of Ni–Au alloy nanowires

Binary alloy nanowires of mutually immiscible Ni–Au system are synthesized by electrodeposition method. Here, we incorporate the concept of alloy design into nanowires to effectively engineer and control the magnetic properties of nanowires. Saturation magnetization and coercivity values of as-deposited Ni–Au alloy nanowires strongly correlate with either the phases present or to the dissolution of gold to nickel. The magnetic properties, however, were significantly affected upon annealing, which is correlated with the structural evolution of a weakly magnetic metastable hcp-Ni phase. We report here the detailed investigation on phase transformations in Ni–Au alloy nanowires and their effect on magnetic properties.

First principles studies of structural, electrical and magnetic properties of semiconductor nanowires

Abstractmagnified imageThis article reviews recent advances in theoretical description of the properties of various III–V and IV–VI nanowires, which have been obtained using simple ab initio methods. The impact of crystal structure, lateral surfaces, passivation of the dangling bonds and quantum confinement on the stability of the nanowires is discussed. The second part of the paper is devoted to the analysis of III–V and IV–VI nanowires doped with various, in particular magnetic, ions. The influence of the crystal structure of the wire on the segregation and formation energies of different dopants and thus on the electric and magnetic properties of the nanowires is shown. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Structure and magnetic properties of the Co x Pt100−x nanowire arrays

Co–Pt alloy nanowires with different components have been successfully fabricated by alternating current (AC) electro-deposition into the nanopores of the anodic aluminum oxide (AAO) template. SEM and TEM images reveal that the nanowires are uniform and parallel to each other. The aspect ratio of nanowires is over 100. XRD and EDS patterns indicate that Co–Pt nanowires are nanocrystalline at room temperature. For the as-prepared samples, the magnetocrystal anisotropy is very small, therefore, Co content and shape anisotropy play a dominant role in contributing to the improvement of coercivity and squareness. Meanwhile, the Co–Pt alloy nanowires transforms from a hard magnetic phase of fcc CoPt to a relatively soft magnetic phase of fcc CoPt3 when the annealing temperature is above 400 °C. The structure and magnetic properties of nanowires after annealing are studied and discussed in this paper.

Preparation of nickel nanowire within polycarbonate membrane and removing polycarbonate by KrF excimer laser

Nikel nanowire arrays were fabricated by potentiostatic electrodeposition into track-etched polycarbonate (PC) membranes. By electrochemical deposition of nickel, nanowires were grown in the single pores. The nanowires were contacted by sputtering a gold layer on top of the membrane. The distinct difference in laser ablation thresholds offers the selective material removal. After preparation of nanowires, polycarbonate membranes were irradiated by KrF excimer laser, 248 nm, at fluence of 0.13 J/cm2, at 1 Hz pulse repetition rate in order to remove polycarbonate. Scanning electron microscopy and X-ray diffraction were employed to characterize the structural and morphological properties of the nanowires. Magnetic properties of nanowires were measured through a magnetization hysteresis curves, using vibrating sample magnetometer (VSM). Key words: Electrodeposition, nanowires, nickel, nuclear track membrane, excimer laser.