H. Han

Silica coated magnetic nanoparticles for separation of nuclear acidic waste

Fe2O3 magnetic nanoparticles (MNPs) have been coated with silica, followed by covalent attachment of the actinide specific chelators to separate nuclear waste in acidic conditions. A general model is developed to relate the surface coating to the particle’s magnetization change, providing an alternative way to characterize the size-distribution/aggregation of MNPs. The optimized silica coating protects the Fe2O3 MNPs from iron leaching under highly acidic conditions, facilitates the dispersion of MNPs, and dramatically increases the loading capacity of chelator onto the MNPs. Compared with the uncoated counterparts, the silica coated MNPs show enhanced actinide separation efficiency.

Metal coatings on SiC nanowires by plasma-enhanced chemical vapor deposition

Coating of nanowires is being investigated to broaden potential uses for future applications. Coatings of Ni and Pt nanoparticles have been synthesized on silicon carbide nanowires by plasma enhanced chemical vapor deposition. Coatings with high particle densities with average particle diameters of 2.76 and 3.28 nm for Pt and Ni, respectively, were formed with narrow size distributions. Plasma enhanced chemical vapor deposition appears to be an efficient method for production of metal coatings on nanowires.

Micromagnetic configurations and switching mechanism in Pac-man-shaped submicron Ni80Fe20 magnets

Micromagnetic modeling analysis and magnetic force microscopy studies were performed in order to characterize the magnetization configuration and magnetic switching behavior in two types, PM I and PM II, of submicron Pac-man-shaped Ni80Fe20 magnetic elements. It was found that a slight variation in the shape of the elements has a striking influence on the internal magnetic structures and switching field distribution. In particular, the vortex-formation driven switching is replaced by quasicoherent reversal by removing the central core part at the center of element. The sensitive dependence of remanent magnetic configuration and switching behavior on sample geometry is discussed in terms of the competition between the exchange and demagnetizing energy terms.

Micromagnetic domain structures and magnetization switching mechanism in submicrometer thin-film elements

Magnetization configuration and magnetic switching behavior in two types, P-I and P-II, of submicrometer Pac-man-shaped Ni/sub 80/Fe/sub 20/ magnetic elements are studied using both magnetic force microscopy (MFM) and numerical simulation. It was found that a slight variation in the shape of the elements has a striking influence on the internal magnetic structures and switching field distribution. In particular, the vortex-formation-driven switching is replaced by quasi-coherent reversal by removing the central core part at the center of element. The sensitive dependence of remanent magnetic configuration and switching behavior on sample geometry is discussed in terms of the competition between the exchange and demagnetizing energy terms.

Interaction effect on switching behaviors of paired "Pac-Man" array

Interactions between neighboring cells become increasingly important due to the miniaturization of magnetoelectronic devices. This paper studies the effect of magnetic interaction on the switching behaviors in two different configurations of paired Pac-man shape Permalloy elements: back-to-back and face-to-face configurations. From as-patterned state MFM images, it is observed that the face-to-face configuration is prone to form either two single domains with an antiferromagnetic configuration, one single domain with one vortex or a double vortex configuration. MOKE hysteresis loops show that the coercivity for the face-to-face configuration is smaller than the back-to-back configuration. These experimental results indicate that the back-to-back configuration has weaker interaction between the two Pac-man elements than the face-to-face configuration. We further varied the aspect ratio of Pac-man elements in the pair arrays to tune the magnetic interaction. It was found that the coercivity of pair array increased with the higher cell aspect ratio. Micromagnetic simulation was also performed to simulate the switching process for the two different configurations. Overall, the back-to-back configuration is recommended for applications that demands less inter-cell interactions.

Coated Magnetic Nanoparticles for Acidic Nuclear Waste Separation

Actinide specific chelator (che) conjugated with magnetic nanoparticles (MNPs) have been developed to separate nuclear waste in acidic conditions. Compared to the traditional nuclear waste treatments, such as solvent extraction and ion exchange, this method is a simple, compact and cost-effective process that generates minimum secondary waste. In this paper, we focus on the coating process of MNPs to achieve a combination of good acidic resistance, high chelator loading density and efficient magnetic separation. An optimized silica coating process before conjugates chelator directly onto MNPs significantly improves the acidic resistance of the MNP-che complex. Chelator loading density is significantly increased by attaching a linear polyamine polymer poly(allylamine hydrochloride) (PAH) to the surface of the MNPs using chemical and physical approaches.

The Effects of Crystallinity and Catalyst Dynamics on Boron Carbide Nanospring Formation

The formation of helical nanowires—nanosprings—of boron carbide have been observed and a growth mechanism, based on the work of adhesion of the metal catalyst and the tip of the nanowire, developed. The model demonstrates that the asymmetry necessary for helical growth is introduced when the following conditions are met: (1) The radius of the droplet is larger than the radius of the nanowire, and (2) The center of mass of the metal droplet is displaced laterally from the central axis of the nanowire. Furthermore, this model indicates that only amorphous nanowires will exhibit this unique form of growth and that in monocrystalline nanowires it is the crystal structure that inhibits helical growth. High-resolution transmission electron microscopy and electron diffraction has been used to compare the structure of both amorphous and crystalline nanowires.

Lateral Size Dependence of Pac-man shaped Ni80Fe20 Element on Magnetization Reversal

The magnetization configuration and switching mechanism of small patterned submicron and micron scaled magnetic elements of Ni80Fe20 thin film having the elongated Pac-man (EPM) shape is performed using micromagnetic simulation. The reduction of lateral size of elongated Pac-man elements decreases the possibility of domain wall formation, which results in increasing the switching speed. However, the magnetization ringing is enhanced for smaller elements due to the high energy supplied to the element to achieve the reversal. The ringing is found to be suppressed from the reduction in the thickness of the thin film to 3.2 nm as seen from other micromagnetic studies performed on elliptical Ni80Fe20 elements.