Pongsakorn Jantaratana

Effects of thickness and heat treatments on giant magnetoimpedance of electrodeposited cobalt on silver wires

We studied the effects of thickness and heat treatments on giant magnetoimpedance (GMI) of cobalt-coated silver wires from 1 kHz to 100 MHz, under axial static magnetic field of 2 kOe. Cobalt, of thickness ranging from 1 to 25 /spl mu/m, was electro-deposited on 47.7-/spl mu/m-diameter silver wires. The frequency dependence of GMI varied with cobalt thickness with a maximum of 176% in 10-/spl mu/m-thick cobalt at the characteristic frequency 2 MHz. The characteristic frequency decreased with increasing thickness of cobalt layer but it was rather insensitive to dc Joule heating and conventional furnace annealing. However, both heat treatments led to magnetic hardening and decrease in GMI ratio. Joule heating also induced anisotropy in wire structures normally dominated by axial anisotropy.

Synthesis and cytotoxicity study of magnesium ferrite-gold core-shell nanoparticles

In this work, the core-magnesium ferrite (MgFe2O4) nanoparticles were prepared by hydrothermal technique. Completed gold (Au) shell coating on the surfaces of MgFe2O4 nanoparticles was obtained by varying core/shell ratios via a reduction method. Phase identification, morphological evolution, optical properties, magnetic properties and cytotoxicity to mammalian cells of these MgFe2O4 core coated with Au nanoparticles were examined by using a combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, UV-visible spectroscopy (UV-vis), vibrating sample magnetometry and resazurin microplate assay techniques. In general, TEM images revealed different sizes of the core-shell nanoparticles generated from various core/shell ratios and confirmed the completed Au shell coating on MgFe2O4 core nanoparticles via suitable core/shell ratio with particle size less than 100 nm. The core-shell nanoparticle size and the quality of coating influence the optical properties of the products. The UV-vis spectra of complete coated MgFe2O4-Au core-shell nanoparticles exhibit the absorption bands in the near-Infrared (NIR) region indicating high potential for therapeutic applications. Based on the magnetic property measurement, it was found that the obtained MgFe2O4-Au core-shell nanoparticles still exhibit superparamagnetism with lower saturation magnetization value, compared with MgFe2O4 core. Both of MgFe2O4 and MgFe2O4-Au core-shell also showed in vitro non-cytotoxicity to mouse areola fibroblast (L-929) cell line.

Magnetoimpedance and magnetization processes of FeCoNi electroplated tubes

The CuBe/Fe20Co6Ni74 electroplated wires were prepared by a standard electrodeposition technique. Heat treatment in a dc magnetic field of 20 Oe applied along the axis of the wire at a temperature of 320 °C for 1 h resulted in a magnetic anisotropy with a longitudinal magnetic anisotropy component. The impedance of the field annealed CuBe/Fe20Co6Ni74 wire strongly depends on the external magnetic field. Very high magnetoimpedence (MI) (up to 600%) and MI sensitivity (up to 570%/Oe) were observed at a relatively low frequency of 1 MHz and a current intensity of 20 mA. Two MI maxima were observed for each branch of the MI responses. These maxima are different from each other: the value of the MI ratio, the MI sensitivity, and the value of the field in which each particular MI maximum appears. The angular dependence of a linear MI effect was studied for specific conditions: f=1 MHz and Irms=20 mA. Detailed analysis of the MI responses indicated the existence of two different types of spin-orientational phase...

Frequency-dependent magnetoelectricity of CoFe2O4-BaTiO3 particulate composites

Abstract CoFe 2 O 4 -BaTiO 3 particulate composites were prepared by wet ball milling method, their magnetoelectric (ME) effect was studied as a function of their constituents and modulation frequency. The results show that the ME coefficient increases as a function of modulation frequency from 400 to 1000 Hz and the ME characteristics of ME curves are also modified because the electrical conductivity of the CoFe 2 O 4 phase is sensitive to the increase in frequency between 400 and 1 000 Hz. The third phase Ba 2 Fe 2 O 5 formed during the sintering tends to reduce the ME effect.

Giant magnetoimpedance of electrodeposited Co/Cu/Co on Ag wires

Giant magnetoimpedance (GMI) was studied in electrodeposited Co/Cu/Co-coated Ag wires with variations in the axial dc magnetic field (0–2 kOe), frequency of ac driving current (1 kHz–100 MHz), thickness of each layer (1.0–25.0 µm) and diameter of the Ag core (47.7 and 120.0 µm). With increasing thickness of coated layers and Ag cores, the maximum GMI ratio increased but the characteristic frequency decreased. Unlike Co-coated Ag wires, the frequency-dependent GMI curves of these multilayered wires were broadened and asymmetric. The GMI behaviours were explained in terms of the distribution of current density and current flow in the coated wires obtained from the finite element method simulation program.

Magnetic Hysteresis and Electrical Impedance Spectra of Hard Magnetic SmCo5 and Soft Magnetic Co30Ag70 Composites

Abstract A Vibrating Sample Magnetometer (VSM) and a set-up for electrical impedance measurement in magnetic field were employed to study Co 30 Ag 70 mechanical alloys with additions of 0%, 5% and 10% (mass fraction) hard magnetic SmCo 5 . With increasing SmCo 5 content, the particulate composites exhibited an increase in the remanent magnetization when the coercive field remained rather constant. The electrical impedance of each composite did not show a large variation between 10 kHz and 100 kHz but rapidly rose with the increase in frequency from around 200 kHz to 1 MHz due to the skin effect. All impedance spectra were slightly shifted when the magnetic field of 3.3 kA/m was applied. The largest difference was observed in the case of Co 30 Ag 70 without SmCo 5 addition. The results confirmed the relationship between the magnetic softness of materials and their electrical impedance in magnetic field.

Magnetic and dielectric properties of natural rubber and polyurethane composites filled with cobalt ferrite

Abstract Cobalt ferrite (CoFe2O4) powders synthesised by sol–gel techniques were incorporated into natural rubber (NR) and polyurethane (PU) by two-roll milling at different loadings from 0 to 45 phr. In either NR or PU composites, the magnetisations were proportional to the CoFe2O4 loading, but the coercive field remained rather insensitive to the loading. The frequency response from 1 MHz to 1 GHz revealed that the real part of the magnetic permeability increased significantly only in the case of 45 phr CoFe2O4, while the imaginary part was modest in both NR and PU composites. In contrast, the electrical permittivity of CoFe2O4–PU was larger than that of CoFe2O4–NR composites, and both parts at 100 MHz had linear variations with the loading, in agreement with Wagner’s equation.

Magnetic Properties and Magnetoimpedance of Electroplated Wires

Magnetic properties and giant magnetoimpedance (GMI) of CuBe/Fe20Co6Ni74 electroplated wires was studied for frequency of 1 MHz and the amplitude of the driving current of 20 mA with focus on the development of magnetic field detectors of particular types. The possibility of quantitative ferrofluid concentration measurements was demonstrated. GMI of electroplated wire can be useful for the study of the dynamic properties of the ferrofluid. GMI of the electroplated wires in the non-uniform field created by the permanent magnet was studied in the configuration adapted for automatic control lines, machinery control, and positioning systems.

Magnetoelectric Properties of Cu- and Mn-Doped 0.75BiFeO3–0.25BaTiO3 Multiferroic Ceramics

In this study, 0.75BiFeO3–0.25BaTiO3 ceramics doped with Mn and Cu (1, 2, 3, 4 and 5 mol%) have been fabricated with an effective solid-state reaction method developed for high purity ceramics. Attention has been focused on relationships between sintering conditions, phase formation, density, and magnetoelectric properties of the sintered ceramics. It was found that Cu and Mn doping affected significantly the dielectric, ferroelectric, ferromagnetic and magnetoelectric properties of these ceramics. At certain level of addition, both Mn and Cu doping were found to enhance the ferroelectric and ferromagnetic characteristics of the BiFeO3-BaTiO3 multiferroic ceramics. Finally, magnetoelectric properties of the ceramics were also determined. The addition of the Cu and Mn ions was found to noticeably improve the magnetoelectric properties of the ceramics.

Magnetic properties of NdFeB-coated rubberwood composites

Magnetic properties of composites prepared by coating lacquer containing neodymium iron boron (Nd-Fe-B) powders on rubberwood were characterized by vibrating sample magnetometry (VSM), magnetic moment measurements, and attraction tests with an iron-core solenoid. The Nd-Fe-B powders were recycled from electronic wastes by the ball-milling technique. Varying the milling time from 20 to 300 min, the magnetic squareness and the coercive field of the Nd-Fe-B powders were at the minimum when the powders were milled for 130 min. It followed that the coercive field of the magnetic wood composites was increased with the milling time increasing from 130 to 300 min. For the magnetic wood composites using Nd-Fe-B obtained from the same milling time, the magnetic squareness and the coercive field were rather insensitive to the variation of Nd-Fe-B concentration in coating lacquer from 0.43 to 1.00 g/cm3. By contrast, the magnetization and magnetic moment were increased with the Nd-Fe-B concentration increasing. Furthermore, the electrical current in the solenoid required for the attraction of the magnetic wood composites was exponentially reduced with the increase in the amount of Nd-Fe-B used in the coating.