One-dimensional Magnetic Nanostructures Research Articles

Formation and Stability of Magnetic Atomic Chains on Vicinal Metal Surfaces

A kinetic Monte Carlo method was used to perform large-scale simulation of one-dimensional magnetic nano-structures on vicinal metal surfaces. Temperature ranges for nanochains’ formation were obtained for different systems. The lifetimes of the nanochains were determined, and their stability is discussed. The dependence of chain lifetime on its length is not linear. In order to be usable at room temperature, magnetic Co chains should have a length of 25–30 atoms.

Biotemplated synthesis of magnetic filaments.

With the aim of creating one-dimensional magnetic nanostructures, we genetically engineered flagellar filaments produced by Salmonella bacteria to display iron- or magnetite-binding sites, and used the mutant filaments as templates for both nucleation and attachment of the magnetic iron oxide magnetite. Although nucleation from solution and attachment of nanoparticles to a pre-existing surface are two different processes, non-classical crystal nucleation pathways have been increasingly recognized in biological systems, and in many cases nucleation and particle attachment cannot be clearly distinguished. In this study we tested the magnetite-nucleating ability of four types of mutant flagella previously shown to be efficient binders of magnetite nanoparticles, and we used two other mutant flagella that were engineered to periodically display known iron-binding oligopeptides on their surfaces. All mutant filaments were demonstrated to be efficient as templates for the synthesis of one-dimensional magnetic nanostructures under ambient conditions. Both approaches resulted in similar final products, with randomly oriented magnetite nanoparticles partially covering the filamentous biological templates. In an external magnetic field, the viscosity of a suspension of the produced magnetic filaments showed a twofold increase relative to the control sample. The results of magnetic susceptibility measurements were also consistent with the magnetic nanoparticles occurring in linear structures. Our study demonstrates that biological templating can be used to produce one-dimensional magnetic nanostructures under benign conditions, and that modified flagellar filaments can be used for creating model systems in which crystal nucleation from solution can be experimentally studied.

Formation of magnetic nanoparticle chains in bacterial systems

Abstract

Magnetic composite nanofibers fabricated by electrospinning of Fe 3 O 4 /gelatin aqueous solutions

We have fabricated magnetic composite nanofibers containing superparamagnetic Fe3O4 nanoparticles by the electrospinning method. Highly dispersed Fe3O4 magnetic nanoparticles were synthesized by one-step co-precipitation of Fe2+/Fe3+ under an alkaline condition with 4 wt% poly(vinyl alcohol) (PVA) aqueous solution as the stabilizer. Gelatin (GE) was used as a polymeric matrix for fabricating the nanocomposites. The prepared Fe3O4/GE composite nanofibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. These composite nanofibers show uniform and continuous morphology with the Fe3O4 nanoparticles embedded in the nanofibers. By studying the magnetic properties of the Fe3O4/GE composite nanofibers, we confirm that the composite nanofibers possess superparamagnetic properties with a high saturated magnetization (Ms = 12.87 emμ g−1) at room temperature. The features of this approach for getting one-dimensional magnetic nanostructure are its simplicity, effectiveness and safety. The Fe3O4/GE nanofibers with superparamagnetic properties would be potentially applied in biomedical field.

Magnetite Crystal Orientation in Magnetosome Chains

One-dimensional magnetic nanostructures have magnetic properties superior to non-organized materials due to strong uniaxial shape anisotropy. Magnetosome chains in magnetotactic bacteria represent a biological paradigm of such magnet, where magnetite crystals synthesized in organelles called magnetosomes are arranged into linear chains. Two-dimensional synchrotron X-ray diffraction (XRD) is applied to cells of magnetotactic bacteria that are pre-aligned with a magnetic field to determine the crystallographic orientation of magnetosomes relative to the chain axis. The obtained pole figure patterns reveal a [111] fiber texture along the chain direction for magnetospirilla strains MSR-1 and AMB-1, whereas a [100] fiber texture is measured for Desulfovibrio magneticus strain RS-1. The [100] axis appears energetically unfavorable because it represents a magnetic hard axis in magnetite, but can be turned into an effective easy axis by particle elongation along [100] for aspect ratios higher than 1.25, consistent with aspect ratios in RS-1 magnetosomes determined earlier. The pronounced fiber textures can be explained either by a strain-specific biological control on crystal orientation at the chain level or by physical alignment effects due to intra-chain magnetic interactions. In this case, biological control of the axis of elongation would be sufficient to influence the crystallographic texture of the magnetosome chain.

One-dimensional ballistic transport with FLAPW Wannier functions

We present an implementation of the ballistic Landauer-B\"uttiker transport scheme in one-dimensional systems based on density functional theory calculations within the full-potential linearized augmented plane-wave (FLAPW) method. In order to calculate the conductance within the Green's function method, we map the electronic structure from the extended states of the FLAPW calculation to Wannier functions, which constitute a minimal localized basis set. Our approach benefits from the high accuracy of the underlying FLAPW calculations, allowing us to address the complex interplay of structure, magnetism, and spin-orbit coupling and is ideally suited to study spin-dependent electronic transport in one-dimensional magnetic nanostructures. To illustrate our approach, we study ballistic electron transport in nonmagnetic Pt monowires with a single stretched bond including spin-orbit coupling, and in ferromagnetic Co monowires with different collinear magnetic alignment of the electrodes with the purpose of analyzing the magnetoresistance when going from tunneling to the contact regime. We further investigate spin-orbit scattering due to an impurity atom. We consider two configurations: a Co atom in a Pt monowire and vice versa. In both cases, the spin-orbit induced band mixing leads to a change of the conductance upon switching the magnetization direction from along the chain axis to perpendicular to it. The main contribution stems from ballistic spin scattering for the magnetic Co impurity in the nonmagnetic Pt monowire, and for the Pt scatterer in the magnetic Co monowire from the band formed from states with ${d}_{xy}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital symmetry. We quantify this effect by calculating the ballistic anisotropic magnetoresistance, which displays values up to as much as 7$%$ for ballistic spin scattering and gigantic values of around 100$%$ for the Pt impurity in the Co wire. In addition, we show that the presence of a scatterer can reduce as well as increase the ballistic anisotropic magnetoresistance.

Magnetic nanofibers with core (Fe3O4 nanoparticle suspension)/sheath (poly ethylene terephthalate) structure fabricated by coaxial electrospinning

One-dimensional magnetic nanostructures have recently attracted much attention because of their intriguing properties that are not realized by their bulk or particle form. These nanostructures are potentially useful for the application to ultrahigh-density data storages, sensors and bulletproof vest. The magnetic particles in magnetic nanofibers of blend types cannot fully align along the external magnetic field because magnetic particles are arrested in solid polymer matrix. To improve the mobility of magnetic particles, we used magneto-rheological fluid (MRF), which has the good mobility and dispersibility. Superparamagnetic core/sheath composite nanofibers were obtained with MRF and poly (ethylene terephthalate) (PET) solution via a coaxial electrospinning technique. Coaxial electrospinning is suited for fabricating core/sheath nanofibers encapsulating MRF materials within a polymer sheath. The magnetic nanoparticles in MRF were dispersed within core part of the nanofibers. The core/sheath magnetic composite nanofibers exhibited superparamagnetic behavior at room temperature and the magnetic nanoparticles in MRF well responded to an applied magnetic field. Also, the mechanical properties of the nanofiber were improved in the magnetic field. This study aimed to fabricate core/sheath magnetic composite nanofibers using coaxial electrospinning and characterize the magnetic as well as mechanical properties of composite nanofibers.

Production of Smooth and Pure Nickel Metal Nanofibers by the Electrospinning Technique: Nanofibers Possess Splendid Magnetic Properties

In the present study, smooth, unceasing, hydrogen-free, and pure nickel metal nanofibers have been synthesized using the electrospinning technique. A sol−gel consisting of nickel acetate tetrahydrate and poly(vinyl alcohol) has been electrospun, and the obtained nanofiber mats were vacuously dried and then calcined in argon atmosphere at 700 °C. The invoked physiochemical characterization instruments assured formation of pure nickel nanofibers with an average diameter of 120 nm after the calcination process. The electrospun nickel nanofibers have revealed unique magnetic properties, with much enhanced coercivities relative to bulk materials. The outstanding features of this approach to get one-dimensional magnetic nanostructure are its simplicity, effectiveness, safety, and ease of assembly.

Ni/Ni3C Core–Shell Nanochains and Its Magnetic Properties: One-Step Synthesis at Low Temperature

One-dimensional Ni/Ni3C core-shell nanoball chains with an average diameter by around 30 nm were synthesized by means of a mild chemical solution method using a soft template of trioctylphosphine oxide (TOPO). It was revealed that the uniform Ni nanochains were capped with Ni3C thin shells by about 1-4 nm in thickness and each Ni core consists of polygrains. The coercivity of the core-shell nanochains is much enhanced (600 Oe at 5 K) and comparable with single Ni nanowires due to the one-dimensional shape anisotropy. Deriving from the distinctive structure of Ni core and Ni 3C shell, this architecture may possess a possible bifunctionality. This unique architecture is also useful for the study on the magnetization reversal mechanism of one-dimensional magnetic nanostructure.

Electrospinning of Fe, Co, and Ni Nanofibers: Synthesis, Assembly, and Magnetic Properties

A general synthetic method has been developed to fabricate and assemble ferromagnetic transition metal nanofibers. By employing the novel electrospinning technique followed by subsequent heat treatment, we have successfully prepared uniform nanofibers of Fe, Co, and Ni with diameters of ∼25 nm and lengths longer than 100 μm. Using a specially designed fiber collector, we can conveniently assemble magnetic nanofibers into aligned arrays. The electrospun magnetic metal nanofibers have unique magnetic properties, with much enhanced coercivities relative to bulk materials. The outstanding features of this approach to get one-dimensional magnetic nanostructure are its simplicity, effectiveness, and ease of assembly. Therefore, electrospun magnetic nanofibers can potentially be used in fabrication of high-density magnetic recording, magnetic sensors, flexible magnets, and spintronic devices.

Fabrication of patterned Au films as supporting templates for one-dimensional magnetic nanostructures

We developed a technique to fabricate one-dimensionally patterned ultrathin Au overlayers on the tungsten surface carbide $\mathrm{W}(110)∕\mathrm{C}\text{\ensuremath{-}}R(15\ifmmode\times\else\texttimes\fi{}3)$ by self-organization. It was found that deposition of 1--3 monoatomic layers of Au on the $R(15\ifmmode\times\else\texttimes\fi{}3)$ carbon superstructure and subsequent annealing at $600\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ lead to the development of a Au overlayer the surface of which is one-dimensionally reconstructed with a periodicity of about $30\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. We present a characterization of this system by electron diffraction, scanning tunneling microscopy, and photoelectron spectroscopy to reveal the chemical composition of the created nanopattern. Eventually, the self-organization of Ni nanowires supported on such patterned Au film is demonstrated.

Carbon Nanotubes Loaded with Magnetic Particles

We describe a simple and versatile technique to produce magnetic tubes by filling carbon nanotubes (CNTs) with paramagnetic iron oxide particles ( approximately 10 nm diameter). Commercial ferrofluids were used to fill CNTs with an average outer diameter of 300 nm made via chemical vapor deposition into alumina membranes. Transmission electron microscopy study shows a high density of particles inside the CNT. Experiments using external magnetic fields demonstrate that almost 100% of the nanotubes become magnetic and can be easily manipulated in magnetic field. These one-dimensional magnetic nanostructures can find numerous applications in nanotechnology, memory devices, optical transducers for wearable electronics, and in medicine.