Magneto-resistance, stress effects, and a self-similar expansion model for the magnetization processes in amprphous wires
The outer shell magnetization process was investigated from the point of view of its effects on longitudinal and transverse magnetoresistance (MR), magnetization, and domain structure observations as well as their stress effects for a Fe/sub 77.5/Si/sub 7.5/B/sub 15/ amorphous wire with a diameter of 125 mu m prepared by rapid quenching in rotating water. The unusual behavior of the initial negative slope observed in the longitudinal MR is explained in terms of a realistic domain structure. A self-similar expansion model is proposed to explain the dynamical response of such a structure under applied fields and/or tensile stresses. It is suggested that the zig-zag domains of the outer shell are stabilized by a square closure domain which expands uniformly while maintaining a self-similar shape up to a threshold field of about 20 Oe and then deforms towards the saturation magnetization. However, this domain structure was destroyed or much deformed by a tensile stress along the wire axis of about 170 MPa in the sample. Such a critical stress depends on the diameter, quenching conditions, alloy composition, etc. This behavior and stabilization of the zig-zag domain by the closure domains give a novel mechanism for the magnetization processes which follow the re-entrant reversal, and are thus useful for the understanding of re-entrant reversal phenomena themselves. >
Magnetoresistive sensors with rapidly solidified Permalloy fibers
The microstructure and properties of Permalloy fibers were studied. Both transverse and longitudinal extraordinary magnetoresistive effects have a positive initial slope due to stress-related rotation of moments in the closure domains and to the coherent rotation of moments in the columns. Fiber response was also investigated as a function of the field direction and angle of incidence, fiber twisting and for strong transverse fields. The results are discussed in terms of the existing models, and a new model is proposed to explain the transerse effect. The structures and operating principles of single- and dual-fiber biased sensors based on the longitudinal effects are presented. Distortions due to overbiasing are accounted for by the pinning and expansion of large-area closure domains with moments tilted by the casting stress. The sensitivity-linearity range product is the same for several bias levels, and a family of sensors was obtained using the same fiber. >
An Ultrasensitive Analytical Method Based on Chemiluminescence Sensing Electrochemical Parallel Catalytic Reaction Event
An ultrasensitive electrochemiluminescence (ECL) method on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed for improving ECL analytical characteristics using vanadate(V) as a representative. Vanadate(V) could be electrochemically reduced to generate vanadate(II) which could be chemically oxidized by potassium periodate to regenerate vanadate(V) and give parallel catalytic wave effect. Then, the reduced product of potassium periodate could react with butyl-rhodamine B to emit a sensitive chemiluminescence signal. The chemiluminescence intensity was correlative with vanadate(V) concentration. The investigation on the electrochemical reaction rate constant (k0) confirmed that the speed of electrochemical reaction was faster than that of the subsequent chemiluminescence reaction. The possibility of the combination of electrochemical parallel catalytic reaction with chemiluminescence signal sensing was proved. The similar ECL behaviors could be observed at zirconia nanowires-Nafion modified electrode. Because of the separation and enrichment effect of the modified electrode on vanadate(V), the selectivity and sensitivity was further improved greatly. Based on these findings, a new concept on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed and an ultrasensitive ECL method for the determination of vanadate(V) was developed at zirconia nanowires-Nafion modified electrode. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of vanadate(V) in the range of 2.0×10−12 mol/L–2.0×10−10 mol/L. The detection limit was 8.0×10−13 mol/L, which was more than 6 orders of magnitude lower than that observed by electrochemical current transduction for electrochemical parallel catalytic reaction at zirconia nanowires-Nafion modified electrode.