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. >
Jitter-less pulse generator elements using amorphous bistable wires
New jitter-less pulse generator elements are presented using amorphous magnetostrictive wires. These elements induce sharp voltage pulses with ∼ 6V/cm2.Oe.turn due to the large Barkhausen jumps and with ∼ 6V/cm3.Oe due to the Matteucci effect using external ac fields of more than 0.1 Oe at frequencies between 0.01 Hz - 10 k Hz. Jitter of the pulse inducing phase is less than 1/10 and the pulse height is about twice that of Wiegand wires, respectively. The critical field of the large Barkhausen jump is controlled by heat treatment, etching, or twisting the wires. These wires are expected to be useful for high-performance pulse generator elements for high resolution rotary encorders by combining them with magnet ring, torque sensors, proximity sensors and magnetometers.
Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine
A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10−7 to 1.0 × 10−4 M with a detection limit of 4.0 × 10−7 M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10−5 M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry.