Solid State Phenomena Vols. 124-126

Abstract: We have studied the magnetic properties of Co-Fe circular dot arrays with various thicknesses and diameters in order to determine the optimum thickness and diameter of these dot arrays with a single-domain state for the transmission of spin information. For the thickness of 10 nm, the magnetic state changes from a multi-domain state to a closure-domain state and further to a single-domain state with decreasing diameter. On the other hand, for the thickness of 30 nm and 50 nm, all magnetic states are in a vortex state, regardless of the diameter. From these results, it is found that the optimum thickness and diameter of Co-Fe circular dots with a single-domain state are, respectively, 10 nm and less than 100 nm.

Abstract: A highly sensitive magnetic sensor using the GMI (Giant Magneto Impedance) effect has been developed. The sensor performance is studied and estimated. The sensor circuitry consists of a Square wave generator (driving source), a sensing element in a form of composite wire of a 20μm copper core electrodeposited with a thin layer of soft magnetic material (Ni₈₀Fe₂₀), two amplifier stages for improving the gain from the sensor element, switching mechanism, scaler circuit, an ac power source driving the permeability of the magnetic coating layer of the sensing element into a dynamic state, and a signal pickup LC circuit formed by a pickup coil and an capacitor .The results showed that for high sensitivity and resolution (10^-7 T), the frequency and magnitude of the ac driving current through the sensing element each has an optimum value, the resonance frequency of the signal pickup LC circuit should be equal to or twice as the driving frequency on the sensing element, and the anisotropy of the magnetic coating layer of the sensing wire element should be longitudinal.

Abstract: Mn-Zn ferrite nanoparticles were fabricated via conventional ball-milling and their magnetic properties were investigated. By ball-milling of Mn0.53Zn0.42Fe2.05O4 agglomerates for 48h with and without a dispersant (Darvan-C (ammonium polymethacrylate)), nanoparticles having average particle size of 60 nm were obtained. The saturation magnetizations (Ms) of thus obtained Mn-Zn ferrite nanoparticles were 49 and 62 emu/g for dispersant-added and dispersant-non-added one, respectively. When the nanoparticles were heat-treated at 400
, however, the Ms became comparable: 63 and 65 emu/g. When the nanoparticles were heat-treated at 600
, moreover, the Ms became comparable with that of bulk ferrites: 75~78 emu/g. These magnetic properties were attributed to the surface spin disorder effects resulting from the coating of organic dispersant molecules on the surfaces of the nanoparticles as well the structural disorder on the surfaces the nanoparticles.

Abstract: The surface of magnetite nanoparticles which have been prepared by coprecipitation method was modified by carboxylic acid group of poly(3-thiophenacetic acid (3TA)). Then the egg white lysozyme was immobilized on the carboxylic acid group of the modification of the magnetite nanoparticles. Lysozyme immobilizing efficiency increased with increasing concentration of 3TA. And the functionalized magnetite particles had higher enzymatic capacity than non-functionalized magnetite nanoparticles.

Abstract: Monodisperse FePt nanoparticles were synthesized by thermal decomposition of Fe(CO)5 and reduction of Pt(acac)2 at low temperature of 160–180 °C by using kerosene as a solvent. The average sizes of the synthesized particles ranged from 2.2 to 4.4 nm. Thermal annealing of the as-prepared FePt particles at 700 °C for 1 h transformed the crystalline structure of the particles from a disordered face-centered cubic to an ordered face-centered tetragonal. This change led to a significant increase in coercivity from 153.37 to 2273.22 Oe and in saturated magnetization from 26.86 to 41.21 emu/g.

Abstract: This work reported the development of the high throughput protein separation process with molecularly assembled silica-coated magnetic nanoparticles as a function of amino group numbers such as mono-, di-, and tri-aminofunctionality, in which the range of silica coating thicknesses were optimized to be interacted with protein. The protein separation efficiency was demonstrated as a function of each aminofunctional group and the particle sizes of the silica coated magnetic nanoparticles. The particles were prepared by the chemical precipitation of Fe2+ and Fe3+ salts with a molar ratio of 1:2 under basic solution. The silica coated magnetic nanoparticles were directly produced by the sol-gel reaction of a tetraethyl orthosilicate (TEOS) precursor, in which the coating layer serves as a biocompatible and versatile group for further biomolecular functionalization. To effectively capture the proteins, silica coated magnetic nanoparticles need to be functionalized reproducibly on the silica surface, and three kinds of amino functional groups were adapted as a function of number of amine using the mono-, di-, and tri-aminopropylalkoxysilanes.

Abstract: The structure and magnetic properties of sequentially deposited Pd-Co and Pd-Co- Fe nanocrystals have been investigated by transmission electron microscopy (TEM) and superconducting quantum interference device magnetometer. The fcc structured PdCo alloy formation was found in binary Pd-Co nanostructured samples analysed by in situ TEM annealing. In ternary sample, the addition of Fe to Pd-Co resulted in a complex of Pd and FeCo nanoparticles. In situ TEM annealing of the ternary sample lead to the formation of L10 ordered phase. It was found that the magnetic properties of the nanoparticles were improved by Fe addition to the Pd-Co nanoparticles.

Abstract: Switching behavior and domain structure greatly depends on the edge shape of mesoscopic patterns. In our simulation, permalloy patterns with elliptical and tapered edge need 80% and 50% more switching field, respectively, than a rectangle for the same overall aspect ratio of four. In the switching dynamics, vortex nucleation and its initial location play a great role in deciding switching field. Elliptical and tapered patterns show high magnetic remanence, which is advantageous for non-volatile device application. It is also demonstrated that small control of tapered edge makes it possible to change the switching behavior without the variation of overall aspect ratio.

Abstract: The hydrogenation characteristics and embrittlement behavior of Ti50Zr(50-x)Cux alloys (x=25,33,40) are reported. The hydrogenation kinetics decreased with increasing Zr-content. Though the Ti50Zr25Cu25 alloy showed the slowest kinetics, it absorbed large amount of hydrogen (~2.4 wt.%) and exhibited the best resistance against hydrogen embrittlement. The excellent characteristics of Ti- Zr-Cu alloys in hydrogen environment indicated that they are promising materials in future for energy applications.