Nano-storage wires

Exploring the Magnetic Properties of Individual Barcode Nanowires using Wide-Field Diamond Microscopy

A barcode magnetic nanowire typically comprises a multilayer magnetic structure in a single body with more than one segment type. Interestingly, due to selective functionalization and novel interactions between the layers, it has attracted significant attention, particularly in bioengineering. However, analyzing the magnetic properties at the individual nanowire level remains challenging. Herein, the characterization of a single magnetic nanowire is investigated at room temperature under ambient conditions based on magnetic images obtained via wide-field quantum microscopy with nitrogen-vacancy centers in diamond. Consequently, critical magnetic properties of a single nanowire can be extracted, such as saturation magnetization and coercivity, by comparing the experimental result with that of micromagnetic simulation. This study opens up the possibility for a versatile in situ characterization method suited to individual magnetic nanowires.

Unveiling the Origin of Multidomain Structures in Compositionally Modulated Cylindrical Magnetic Nanowires

CoNi/Ni multisegmented cylindrical nanowires were synthesized via an electrochemical route. The wires are 140 nm in diameter, with 1000 nm long Ni segments and CoNi segments between 600 and 1400 nm in length. The magnetic configuration was imaged by XMCD-PEEM in the demagnetized state and at remanence after magnetizing axially and perpendicularly. Ni segments, with cubic crystal symmetry, show an axial magnetic configuration with a small curling component at the surface. In turn, CoNi segments, with hexagonal crystal symmetry and a strong magnetocrystalline anisotropy perpendicular to the nanowires, show a single vortex state in the shorter segments and multivortex or multitransverse magnetic configurations in medium and long segments, respectively. A detailed study by micromagnetic simulations reveals that the magnetic configuration is determined mainly by the coupling between soft Ni and harder CoNi segments. For short CoNi segments, Ni segments are magnetostatically coupled and the chirality of the single vortex formed in CoNi remains the same as that of the curling in neighboring Ni segments. For longer CoNi segments, the remanent state is either the multivortex or multitransverse state depending on whether the previously applied field was parallel or perpendicular to the magnetocrystalline axis. The results point out the relevance of the cylindrical geometry to promote the occurrence of complex magneto-chiral effects and provide key information for the design of cylindrical magnetic nanowires for multiple applications.

Constructing a Green Light Photodetector on Inorganic/Organic Semiconductor Homogeneous Hybrid Nanowire Arrays with Remarkably Enhanced Photoelectric Response

We demonstrate that a novel photodetector is constructed by CdS/poly( p-phenylene vinylene) (PPV) homogeneous hybrid nanowire arrays via a simple template-assisted electrochemical codeposition approach. Owing to the well-matched energy levels between CdS and PPV, the recombination of photogenerated electrons and holes in CdS/PPV hybrid nanowire arrays is greatly inhibited. It is found that the homogeneous hybrid nanowire arrays exhibit remarkably enhanced photoelectric response and the ON/OFF ratio by 17 times compared to the individual CdS component. More importantly, the CdS/PPV hybrid nanowire arrays are observed with significant spectral selectivity especially for green light under 545 nm. In addition, a straight linear relationship is obtained between the ON/OFF ratios and the illumination intensities, implying that the quantitative detection of illumination intensity can be achieved. The new as-prepared homogeneous hybrid organic/inorganic semiconductor nanowire arrays have a bright prospect for applications in high-sensitivity and high-speed green photodetectors.

Magnetic imaging of a single ferromagnetic nanowire using diamond atomic sensors

Recent advances in nanorobotic manipulation of ferromagnetic nanowires bring new avenues for applications in the biomedical area, such as targeted drug delivery, diagnostics or localized surgery. However, probing a single nanowire and monitoring its dynamics remains a challenge since it demands high precision sensing, high-resolution imaging, and stable operations in fluidic environments. Here, we report on a novel method of imaging and sensing magnetic fields from a single ferromagnetic nanowire with an atomic-scale sensor in diamond, i.e. diamond nitrogen-vacancy (NV) defect center. The distribution of static magnetic fields around a single Co nanowire is mapped out by spatially distributed NV centers and the obtained image is further compared with numerical simulation for quantitative analysis. DC field measurements such as continuous-wave ODMR and Ramsey sequence are used in the paper and sub Gauss level of field sensing is demonstrated. By imaging magnetic fields at a single nanowire level, this work represents an important step toward tracking and probing of ferromagnetic nanowires in biomedical applications.

Magnetization Ratchet in Cylindrical Nanowires

The unidirectional motion of information carriers such as domain walls in magnetic nanostrips is a key feature for many future spintronic applications based on shift registers. This magnetic ratchet effect has so far been achieved in a limited number of complex nanomagnetic structures, for example, by lithographically engineered pinning sites. Here we report on a simple remagnetization ratchet originated in the asymmetric potential from the designed increasing lengths of magnetostatically coupled ferromagnetic segments in FeCo/Cu cylindrical nanowires. The magnetization reversal in neighboring segments propagates sequentially in steps starting from the shorter segments, irrespective of the applied field direction. This natural and efficient ratchet offers alternatives for the design of three-dimensional advanced storage and logic devices.

Applications, Surface Modification and Functionalization of Nickel Nanorods

The growing number of nanoparticle applications in science and industry is leading to increasingly complex nanostructures that fulfill certain tasks in a specific environment. Nickel nanorods already possess promising properties due to their magnetic behavior and their elongated shape. The relevance of this kind of nanorod in a complex measurement setting can be further improved by suitable surface modification and functionalization procedures, so that customized nanostructures for a specific application become available. In this review, we focus on nickel nanorods that are synthesized by electrodeposition into porous templates, as this is the most common type of nickel nanorod fabrication method. Moreover, it is a facile synthesis approach that can be easily established in a laboratory environment. Firstly, we will discuss possible applications of nickel nanorods ranging from data storage to catalysis, biosensing and cancer treatment. Secondly, we will focus on nickel nanorod surface modification strategies, which represent a crucial step for the successful application of nanorods in all medical and biological settings. Here, the immobilization of antibodies or peptides onto the nanorod surface adds another functionality in order to yield highly promising nanostructures.

Co/Au multisegmented nanowires: a 3D array of magnetostatically coupled nanopillars

Arrays of multisegmented Co/Au nanowires with designed segment lengths and diameters have been prepared by electrodeposition into aluminum oxide templates. The high quality of the Co/Au interface and the crystallographic structure of Co segments have determined by high-resolution transmission electron microscopy. Magnetic hysteresis loop measurements show larger coercivity and squareness of multisegmented nanowires as compared to single segment Co nanowires. The complementary micromagnetic simulations are in good agreement with the experimental results, confirming that the magnetic behavior is defined mainly by magnetostatic coupling between different segments. The proposed structure constitutes an innovative route towards a 3D array of synchronized magnetic nano-oscillators with large potential in nanoelectronics.

"Bio-switch Chip" Based on Nanostructured Conducting Polymer and Entrapped Enzyme

We report a switchable biochip strategy where enzymes were entrapped in conducting polymer layers and the enzymatic reaction of the entrapped enzymes was controlled in real-time via electrical stimuli on the polymer layers. This device is named here as a "bio-switch chip" (BSC). We fabricated BSC structures using polypyrrole (Ppy) with entrapped glucose oxidase (GOx) and demonstrated the switching of glucose oxidation reaction in real-time. We found that the introduction of a negative bias voltage on the BSC structure resulted in the enhanced glucose oxidation reaction by more than 20 times than that without a bias voltage. Moreover, because the BSC structures could be fabricated on specific regions, we could control the enzymatic reaction on specific regions. In view of the fact that enzymes enable very useful and versatile biochemical reactions, the ability to control the enzymatic reactions via conventional electrical signals could open up various applications in the area of biochips and other biochemical industries.

Crystallographically driven magnetic behaviour of arrays of monocrystalline Co nanowires

Cobalt nanowires, 40 nm in diameter and several micrometers long, have been grown by controlled electrodeposition into ordered anodic alumina templates. The hcp crystal symmetry is tuned by a suitable choice of the electrolyte pH (between 3.5 and 6.0) during growth. Systematic high resolution transmission electron microscopy imaging and analysis of the electron diffraction patterns reveals a dependence of crystal orientation from electrolyte pH. The tailored modification of the crystalline signature results in the reorientation of the magnetocrystalline anisotropy and increasing experimental coercivity and squareness with decreasing polar angle of the 'c' growth axis. Micromagnetic modeling of the demagnetization process and its angular dependence is in agreement with the experiment and allows us to establish the change in the character of the magnetization reversal: from quasi-curling to vortex domain wall propagation modes when the crystal 'c' axis tilts more than 75° in respect to the nanowire axis.