Search

In situ measurements of resistance were made on cosputtered [Co.sub.0.35][[Si[O.sub.2].sub.0.65]] granular films during annealing. The aim is to control the thermal treatment parameters and map the microstructural changes of the samples, with the respective magnetotransport response. Results of transmission electron microscopy, dc magnetization, and temperature dependence of resistivity, after annealing, show a clear evolution in the nanostructure of the samples, with increasing average Co grain sizes and wider dispersion. Index Terms--Heat treatment, magnetic films, magnetoresistance.

The effect of torsional stresses in the magnetoimpedance response of a [([Co.sub.0.94][Fe.sub.0.06]).sub.72.5][Si.sub.12.5][B.sub.15] amorphous wire is analyzed. In particular, the occurrence of a second-harmonic contribution of the magnetoimpedance voltage is analyzed and compared with the first-harmonic amplitude (impedance). The evolution of both harmonic components are correlated to the estimated permeability contributions obtained through the analysis of the estimated rotational hysteresis loops. The highest torsional dependence of the second-harmonic contribution can be used in the development of new magnetoelastic sensors. Index Terms--Amorpbous wire, magnetoelasticity, magnetoimpedance effects, permeability.

A study of giant magnetoresistance (GMR) has been performed on melt-spun ribbons of [Cu.sub.100-x][Co.sub.x] (5 [less than or equal to] x [less than or equal to] 20) subjected to DC Joule heating in order to optimise the GMR response. The GMR results, plotted as functions of the reduced magnetisation, exhibit significant deviations from the parabolic behavior predicted in the case of no correlation among magnetic moments. A simple theory of the GMR in Cu-Co granular systems, taking explicitly into account the correlation existing among the magnetic particles, is highlighted. The effect of both Co content and degree of magnetic correlation on the maximum GMR values attained for each composition is briefly discussed.

The effect of particle size distribution on the magnetic properties of nanocrystalline [Fe.sub.86][Zr.sub.7][Cu.sub.1][B.sub.6] samples is studied in detail. The analysis applies a realistic particle size distribution, obtained from transmission electron microscopy images, to the recently developed extended Random Anisotropy Model. The effect of a broad size distribution is found to be more relevant when the tail of the distribution is larger than 20 nm. Index Terms--Nanocrystalline materials, soft magnetic materials, random anisotropy model.

On-line measurements of resistance and temperature in melt-spun [Cu.sub.90] [Co.sub.10] ribbons are made using two different annealing techniques: conventional furnace annealing, and linearly varying current Joule heating. The aim of this paper is to consider the current, flowing through the sample during the annealing, as a possible parameter to control thermal treatment parameters and thus the microstructure of these systems. Although an exact way to obtain the temperature from the annealing current remains a difficult task, the on-line changes in resistance with current allows one to identify structural changes in the sample during annealing. Also, because the temperature is found to increase continuously with electrical current, it is possible to calibrate the Joule heating system to precisely determine the annealing temperature. Index Terms--Joule heating, binary alloys, nanocrystalline materials.