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.     

Structural and magnetic properties of cobalt ferrites synthesized using sol-gel techniques

Cobalt ferrite (CoFe₂O₄) was synthesized using sol-gel techniques from cobalt nitrate: iron nitrate: polyvinyl alcohol (PVA) gel in a ratio of 1:2:12. Variations in the amount of PVA in water (5 %, 10 % and 15 %) influenced the crystallite size and phases of the ferrite products, which in turn controlled their magnetic properties. X-ray diffraction studies indicated single phase CoFe₂O₄ with larger crystallite size and with the hysteresis loops displaying an increase in both coercive field and squareness as the PVA content was increased. Differential scanning calorimetry (DSC) showed that desorption of water and combustion of excess gel were clearly observed in CoFe₂O₄ prepared from 10 % and 15 % PVA in water. In the case of 5 % PVA in water, two other ratios of cobalt nitrate: iron nitrate: PVA solution were also tested and it was found that the 1:2:10 ratio led to the smallest coercive field and squareness.     

Electromagnetic and Dynamic Mechanical Properties of Extruded Cobalt Ferrite-Polypropylene Composites

Cobalt ferrites of 0–45 wt% were incorporated in polypropylene by the extrusion technique. With increasing magnetic loading, the magnetizations were linearly increased according to the rule of mixture and the electrical permittivity was also proportional to the loading as described by Wagner's equation. The magnetic permeability may be increased but was reduced to minimal at high frequencies because of the substantial coercive field of cobalt ferrites after the extrusion. Without considerable adsorption of polymer matrix on magnetic fillers, the storage and loss modulus from 30 to 180°C of polypropylene were decreased by cobalt ferrites additions.     

Phase Transformations in Mn–Al and Mn–Bi Magnets by Repeated Heat Treatment

Transactions of the Indian Institute of Metals - A stepped heating cycle in a tube furnace at 1000 °C for 1 h followed by holding at 400 °C for 1 h...     

Quantitative Analysis of X-ray Lithographic Pores by SEM Image Processing

Arrays of regular macropores in electronic, magnetic, photonic and sensing devices can be patterned by X-ray lithography. Such structures inevitably contain some irregularity and require time-consuming pattern inspections. In this work, a pattern inspection by intensity-based digital image processing procedure is proposed and tested on scanning electron microscopy images of porous SU-8 polymer resist. The Otsu’s thresholding converted grayscale to binary images and the closing morphology algorithm was applied to reduce noise in the images. The Canny edge detector was used to identify the contour of each pore by detecting abrupt intensity changes in the binary image. Pores were detected and their sizes were subsequently evaluated. The morphological distributions analyzed by this procedure are comparable to those carried out by the one-by-one human inspection.     

Cure and mechanical properties of recycled NdFeB-natural rubber composites

Magnetic polymer composites containing recycled neodymium-iron-boron (NdFeB) powder and natural rubber (NR) were prepared by the two-roll mill technique. Their mechanical and cure properties were studied as a function of NdFeB loading from 0–120 phr. With increasing magnetic loading, the cure time of the NdFeB-NR composites were exponentially decreased because of the reduction of the polymer chain crosslink. The tensile strength of the NR compound, related to the cure characteristics, was reduced by 40% by the addition of 10 phr NdFeB fillers because of the inhibition of the stress-induced crystallization. However, the variation in loading from 30–90 phr has modest effects on the tensile strength as well as elongation at break and the hardness. Furthermore, recycled NdFeB-NR composites had higher modulus and lower percentage of swelling in this magnetic loading regime. Simple tests confirmed the distribution of magnetic stray field around pieces of NdFeB-NR composites.     

CoFe_2O_4-BaTiO_3颗粒复合材料的频率相关电磁性能

通过湿法球磨制备CoFe2O4-BaTiO3颗粒复合材料,研究材料成分和调制频率与电磁效应的关系。结果表明：电磁效应系数随着调制频率由400Hz增加到1000Hz而增加。由于CoFe2O4的电导率在400-1000Hz范围内对频率敏感,电磁效应的曲线特性而发生改变。在烧结过程中形成第三相Ba2Fe2O5,从而导致电磁效应的下降。     

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

在磁场下,采用振动样品磁强计和电阻抗测试仪来研究加入 0%,5% 和 10%(质量分数)的硬磁钐钴的钴银合金在矫顽场不变的情况下,颗粒状复合材料的剩余磁化强度伴随钐钴质量分数的增加而增加。在 10 kHz~100 kHz 区间,各复合材料的电阻抗均未表现大的变化。但是,在 200 kHz~1 MHz 区间,由于趋肤效应,电阻抗迅速增加。当磁场为 3.3 kA/m,所有的阻抗谱都发生了微移。其中,未加钐钴的钴银合金阻抗谱发生了最大的偏移。这些结果确定了在磁场下材料软磁特性与其电阻抗的关系。     

Color and hardness of durian chips irradiated by controlled low power microwave

Durian cv. Monthong was dried by using controlled low power microwave at atmospheric pressure. Although the hardness of durian chips was higher than that obtained from microwave drying in vacuum, it was comparable to the hardness of conventional products. According to Hunter Lab color parameters, durian surfaces became lighter but their yellowness was decreased after the microwave drying. Compared between 16 and 27 W irradiations, the higher power led to the increase in lightness and yellowness. Cross-sectional micrographs revealing the porous structure confirmed that a lower hardness was obtained in the case of 16 W.