D. Atkinson

An integrating magnetic sensor based on the giant magneto-impedance effect

A novel magnetic field sensor, based on the giant magneto-impedance effect is described and analysed. The sensor utilises an annealed amorphous wire that can be up to 10 m long, and integrates the field over the length of the wire. It operates in an open-loop mode. With a bias field of 500 A/m, it achieves a sensitivity of 0.02 A/m and linearity of better than 5% for external fields between ±300 A/m.

Magneto-impedance and /spl Delta/E measurements of iron- and cobalt-based amorphous wires

Magneto-impedance and /spl Delta/E measurements of amorphous wires having the compositions Fe/sub 77.5/Si/sub 10/B/sub 15/ and Co/sub 72.5/Si/sub 12.5/B/sub 15/ in the as-quenched and annealed states are presented. The results are interpreted in the light of the widely accepted core-shell domain models for positively and negatively magnetostrictive amorphous wires respectively. It is concluded that in wires of Fe/sub 7.5/Si/sub 10/B/sub 15/ the radial easy axis structure in the shell of the as-quenched wire weakens after light annealing, eventually giving way to a circumferential structure when surface crystallization occurs. In wires of Co/sub 72.5/Si/sub 12.5/B/sub 15/ significant circumferential anisotropy is inferred in all states of annealing studied.

Design of a digitally based /spl Delta/E measurement system

The magnetic field dependence of Youngs modulus is a useful technique for probing the magnetic moment configuration and the anisotropy energy density of magnetostrictive soft magnetic materials. More recently, a high resolution vibrating reed system, based on the closed loop operation of an analogue lock in amplifier (LIA), coupled with an analogue voltage controlled oscillator (VCO) has been used. This system has shown that such measurements are capable of providing new information about subtle domain rearrangements during magnetisation of as-cast amorphous wires. The performance of this system is limited by the use of the analogue components, especially the VCO, to a resolution of a few parts in 10/sup 5/. To overcome this limitation a digital LIA and a function generator which employs digital frequency synthesis methods have been used in a new system. This offers an order of magnitude reduction in noise, with a frequency stability of better than 10/sup -6/ HZ, which can provide a resolution better than 2 parts in 10/sup 6/ for Youngs modulus. Example of data obtained are included. >

High Resolution /spl delta/E Measurements Of Fe-Si-B Amorphous Wire

The field dependence of Youngs modulus, E(H), of as-cast Fe-based amorphous wire has been investigated using a high resolution vibrating reed system. The E(H) data have been combined with DC M(H) loops and Kerr effect surface domain images to provide information about the effect of the large Barkhausen jump which characterizes the magnetization reversal in this material. At low fields the modulus decreases via an abrupt small step which correlates with the field at which the large Barkhausen jump occurs in the M(H) behavior. It is suggested that the reversal of the magnetization in the core domain leads to a slight rearrangement of domains in the sheath region of the wires. This is supported by the surface domain images and indicates a small asymmetry in the remanence states. >

Magnetoelastic properties of annealed Co72.5Si12.5B15 amorphous wires

Abstract We report measurements of the ΔG effect and magnetomechanical damping in as-quenched and annealed amorphous wires of Co 72.5 Si 12.5 B 15 having a saturation magnetostriction λ s of about −3 × 10 −6 . Samples were measured in the as-quenched state, and after annealing at 450°C for times between 30 s and 1000 min. ΔG of up to 10% and magnetomechanical damping up to 0.004 have been found.

Domain structure studies by means of high-resolution /spl Delta/E measurements

High-resolution measurements of the field dependence of the Youngs modulus are reported for two compositions of as-quenched amorphous wires, and for a sputtered thin film of metallic glass. The data reveal details of moment rotation processes that, combined with magnetization and magnetostriction measurements, help to elucidate the domain structures. The results for the amorphous wires show that for the Co-based composition no irreversible moment rotation is associated with the large Barkhausen effect, unlike the behaviour of Fe-based wire. The results for the sputtered film show that the hysteretic magnetization involves almost entirely 180/spl deg/ domain wall movement. >