S. Thongmee

Enhancement of room temperature ferromagnetism in C-doped ZnO films by nitrogen codoping

The effect of nitrogen on the magnetic properties of C-doped ZnO has been investigated. It has been found that a low concentration of N doping does not lead to an apparent change of the magnetization in C-doped ZnO films. When N doping concentration exceeds 0.05 at. %, the magnetization of C–ZnO films increases significantly (more than 85%). The increased magnetization is mainly due to the enhanced moment of carbon, resulted from N doping. The successful fabrication of p-type diluted magnetic semiconductor may be of interest for spintronic applications.

FePt films fabricated by electrodeposition

In this work, we have fabricated FePt films with a thickness in the range of 0.1–1μm using the combination of electrodeposition and postannealing. FePt films with a composition around Fe50Pt50 were formed by electrodeposition onto the Si (100) substrates with an underlayer of Au, Ag, or Cu, and subsequently annealed at a temperature in the range of 200–900°C for 20min. From our x-ray diffraction analysis, the L10 FePt phase started to form after annealing at 400°C for the film deposited on the Au underlayer. The highest coercivity (10kOe) was found after annealing at 600°C. When the FePt was deposited on the Ag underlayer, a high coercivity over 15kOe with an out-of-plane anisotropy has been achieved after annealing at 700–800°C. The magnetic anisotropy was associated with the crystallographic texture. The magnetic properties of FePt films deposited on the Cu underlayer were relatively poor with lower values of coercivity (4–5kOe as the maximum coercivity), probably due to the large grain size.

Synthesis And Characterization Of Ferromagnetic Nanowires Using Aao Templates

Ferromagnetic (Ni, Co, Fe) nanowires were electrodeposited using AAO template. XRD analysis indicated that the ferromagnetic wires had preferred orientation. For longer deposition time, the nanowires with textured structure changed to single crystal. The investigation on the growth mechanism showed that in the initial stage, the nanowires were polycrystalline. Our TEM analysis revealed the transition from polycrystalline structure to single crystal from the bottom to the top. The growth mechanisms are probably due to the competition growth of the adjacent grains and the confinement of growth in the nano-sized hole of the AAO template.

Effect of Sputtered Seed Layer on Electrodeposited NiFe/Cu Composite Wires

In this paper, a seed-layer approach to electrodeposition of Ni 80Fe20 on Cu wires was developed. First, different thicknesses of Ni80Fe20 were directly deposited onto the Cu wires by sputtering as a seed layer. A rotation L-holder fixture was used to hold the Cu wire during sputtering. Second, a relatively thick Ni80Fe20 layer was deposited by electrodeposition onto the Cu wire with the seed layer by sputtering. The results of surface characterization on the composite wires with a seed layer showed that the surface uniformity was greatly improved, as compared to the surfaces of electrodeposited wires without a seed layer. A low coercivity of 0.5 Oe for the composite wire with a seed layer was achieved. The electrodeposited wires with seed layers performed an enhanced MI effect of 250%, in contrast to the MI effect of 160% as achieved by electrodeposited wires without a seed layer

Aging Time Effect on the Formation of Alumina Nanowires on AAO Templates

This article presents the fabrication of alumina nanowires by etching AAO templates using chromic acid solutions. Our work has shown that an aging process in the ambient atmosphere for a relatively long time is indispensable to obtain uniform, small diameter alumina nanowires, which may be due to the release/redistribution of internal stresses of AAO template. The study of the formation mechanism leads to the optimization of the fabrication procedure. Alumina nanowires with a diameter of 5–10 nm have been achieved with a very good uniformity, an excellent surface coverage, and a relatively large BET surface of ∼ 50 m 2 /g.

Magnetic Properties of Highly-Ordered Ni, Co and Their Alloy Nanowires in AAO Templates

We have fabricated metal/alumina hybrid materials by electrodepositon of metal nanowires into nanopores of anodic aluminum oxide templates. Single crystalline Ni and Co nanowires have been successfully fabricated. Structural characterization (XRD and HRTEM) shows that the single crystalline Ni nanowire has a preferred orientation along (220) direction. The preferred orientation of Co nanowire is along (100). These single crystalline Ni and Co nanowires have exhibited excellent magnetic properties. Their alloy nanowires have exhibited a large shift in hysteresis, probably due to the surface oxidation and exchange bias effect.

The structure and magnetic properties of NiO with different sizes

NiO was prepared by co-precipitation followed by an annealing. The fabricated powers showed cluster structures when the annealing temperature was 170degC and the powders showed a dominant ferromagnetic coupling with a magnetization of 105 emu/g. When the annealing temperature was higher than 170degC, the powders showed a nanocrystalline structure composed of surface spins and antiferromagnetic core. Exchange bias was observed after field cooling in these powders. Spin glass and superparamagnetism behaviors were found in the cluster NiO and nanocrystalline NiO, respectively.

Fabrication and magnetic properties of metal nanowires via AAO templates

Metals (Ni, Co, Cu and Fe) nanowires were fabricated by electrodeposition onto anodic aluminum oxide (AAO) template. In this work, we have studied the effect of the electrode potential on the microstructure and magnetic properties of nanowires. TEM results showed that Cu, Co and Ni nanowires were single crystal. Cu and Ni nanowires had the same orientation along the [220] direction, while Co had a preferred orientation along [100] direction. The growth mechanisms are probably due to the competition growth of the adjacent grains and the confinement of growth in the nano-sized hole of the AAO template. Single crystal Fe nanowires could not be formed by the application of different potentials. Ni, Co and Fe showed good magnetic properties. The coercivities up to 1.3 kOe and 1.6 kOe were obtained in Co and Fe nanowires with high remanence ratios 79.7% and 84.8% for Co and Fe, respectively. The remanence ratio of Ni was 97.9%.

Magnetic properties and magneto-impedance effect of CoNiFe/Cu composite wires by electroplating

In this study, CoNiFe/Cu composite wires were deposited using electroplating. The deposited material composition was controlled by adjusting the concentration of Co ions. The results showed that the surface morphology and particle size did not change much with different compositions. However, the coercivity of the composite wires varied significantly for different compositions. A magnetic layer, with the composition of Co30Ni50Fe20, was found to possess a low coercivity value of 0.65 Oe. This is due to the low magneto-strictive factor for the alloy with this composition. In addition, the results showed that the concentration of Fe ions played an important role in achieving low coercivity and high magneto-impedance (MI) effect in the CoNiFe/Cu wires.

Microstructure Evolution of Ni

A study of the microstructure evolution of Ni80Fe20-Cu composite wires made by electrodeposition under an applied magnetic field is presented. Ni80Fe20-Cu composite wire samples were deposited by electroplating under an applied field parallel to the wire axis and varying from 0 to 400 Oe. Magnetoimpedence (MI) measurement showed that the magnitude of MI first scaled with the increasing of the applied field until the field was larger than 200 Oe. Further increasing the applied field led to the reduction of MI effect. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicated that the surface deposited under the applied field of 200 Oe was the best in terms of smoothness and uniformity, indicating that the applied field affected the growth of the deposited layers. The composite wire under 200 Oe applied field possessed a low coercivity (0.35 Oe) and small grain size, which may be attributed to the high MI effect. The surface morphology change is due to the magnetohydrodynamic (MHD) effect