S.N. Hogsdon

Implications of magnetic and magnetoelastic measurements for the domain structure of FeSiB amorphous wires

The field-dependence of magnetization, Youngs modulus and magnetostriction have been used to investigate the domain structure of FeSiB amorphous wires. The experimental observations of the as-cast wire are explained in terms of a modified core-shell model in which the shell is magnetized in a series of domains oriented approximately perpendicular to the wire axis and the magnetization in the core is oriented at an average angle of about 44 degrees to the wire axis. The presence of reverse spike domains in the core at the ends of the wire is also suggested. The critical length below which magnetic bistability is lost may be associated with these reverse domains. The behaviour of wires annealed at 425 degrees C can be interpreted in terms of a similar model, except that the core volume and the length of the reverse spike domains are increased and the average magnetic moment angle in the core is decreased.

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. >

Comparison of magnetoelastic resonance and vibrating reed measurements of the large ΔE effect in amorphous alloys

Abstract Determination of the Δ E effect in Fe-rich amorphous alloys is a delicate task. In this work we compare two commonly used methods to determine its magnitude: the vibrating reed method and the magnetoelastic resonance method. Measurements have been performed on Fe 67 Co 18 Si 14 B 1 and Fe 40 Ni 40 B 20 amorphous ribbons, and the observed differences are discussed.

The use of high-resolution ΔE measurements to study domain processes in soft ferromagnets

Abstract Measurements of the field dependent Youngs modulus with resolution of parts in 10 6 allow domain processes to be studied in a novel way. Examples are given of the use of the technique for studying amorphous (Fe 0.06 Co 0.94 ) 72.5 Si 12.5 B 15 wires and the evolution of the nanocrystalline phase in Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ribbons.

Study of nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 16.5/B/sub 6/ ribbons by high-resolution /spl Delta/E measurements

Measurements of the field dependence of Youngs modulus (/spl Delta/E effect) are reported for amorphous ribbons of Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 16.5/B/sub 6/ annealed for 1 hour at temperatures of 450/spl deg/C, 520/spl deg/C, 540/spl deg/C and 620/spl deg/C. The magnitude of the effect varies from 36% to less than 10/sup -5/ as the magnetostriction constant /spl lambda//sub s/ is reduced by nanocrystallization. The results are discussed in the light of existing models, and suggest that the anisotropy is the result of competition between stress, magnetocrystalline and shape contributions.

Domain processes in grain-oriented silicon steel studied by means of Δ E effect

Abstract Measurements of the field and magnetization dependence of Youngs modulus have been made using [100], [110] and [111] samples of grain-oriented 3.5% silicon steel. Results are presented for the field along and perpendicular to the sample axis. The results are interpreted in terms of domain structures previously proposed. Significant amounts of 90° wall motion are required to account for the behaviour of the [100] sample.

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.