Cornelia Hison

Ni-Ag thin films as strain-sensitive materials for piezoresistive sensors

Abstract Some results concerning the electrical, electromechanical and structural properties of Ni x –Ag 1− x (for x values between 0.35 and 0.50) thin films in view of their utilization for manufacturing pressure and force sensors are presented. As compared to the well known Ni–Cu (constantan) alloys, which are widely used for these type of sensors, Ni x –Ag 1− x thin films exhibit gauge factor values of the same order of magnitude, but they are much more corrosion resistant and adherent to the substrate. The influence of composition and post-deposition annealing on the electrical resistance, temperature coefficient of resistance and gauge factor of Ni x –Ag 1− x thin films is discussed.

Mechanical behavior of nanocrystalline Fe–Hf–B ribbons

Abstract Investigation of annealing type (furnace annealing, direct current (DC) Joule heating, furnace pre-annealing followed by DC Joule heating) influence on the mechanical behavior (brittleness) of Fe–Hf–B nanocrystalline ribbons is presented. The results show a win of two orders of magnitude in terms of brittleness for furnace pre-annealing followed by DC Joule heating with respect to furnace annealing or DC Joule heating.

Torsion and magnetic field measurements using inverse Wiedemann effect in glass-covered amorphous wires

Abstract This paper presents results concerning inverse Wiedemann effect (IWE) dependence on the torsion and d.c. magnetic field applied along the length of the Fe77.5Si7.5B15 glass-covered amorphous wires tested in the as-cast state both before and after glass removal. In the absence of torsion during measurements, the IWE voltage is zero. Increasing the torsion value up to about 55 rad/m increases the value of the induced voltage until it reaches a maximum. In the 0.02–0.03 mT range there is a linear dependence of the IWE voltage on the d.c. magnetic field. The obtained results suggest the possibility of using Fe77.5Si7.5B15 glass-covered amorphous wires as sensing elements for torsion and magnetic field, based on the IWE.

Magnetoelastic behaviour in Co-based glass covered amorphous wires

The effects of Fe content as well as the dc or ac stress current annealing conditions (current density, annealing time, and tensile stress) on the magnetoelastic behavior of amorphous Co/sub 72.5-x/Fe/sub x/Si/sub 12.5/B/sub 15/ (x=0, 3, 4.35, 5, and 7. at.%) glass-covered wires have been investigated. The saturation magnetostriction at zero applied stress /spl lambda//sub s/ (0) in the as-cast state of the samples is about -2.8/spl times/10/sup -6/; -0.6/spl times/10/sup -6/; -0.11/spl times/10/sup -6/; 0.36/spl times/10/sup -6/, and 0.9/spl times/10/sup -6/ for x=0, 3, 4.35, 5, and 7 at.% Fe, respectively. For nearly zero magnetostrictive amorphous Co/sub 68.15/Fe/sub 4.35/Si/sub 12.5/B/sub 15/ glass-covered wire, after stress current annealing /spl lambda//sub s/ (0) changes from small negative to small positive values. The positive /spl lambda//sub s/ (0) values are obtained after about 3-8 min annealing time for current densities higher than 130/spl times/10/sup 6/ A/m/sup 2/. The ac stress current annealing leads to an increase with maximum 60% of the maximum saturation magnetostriction value /spl lambda//sub s/ (0)/sub max/ (depending on the frequency value) in comparison with dc annealing for the same current density, treatment time, and tensile stress. For alloys with x=0, 3, 5, and 7 at.% Fe, after dc or ac stress current annealing with (60-180)/spl times/10/sup 6/ A/m/sup 2/, under 300-800 MPa, a modification up to 10% in /spl lambda//sub s/ (0) values was observed (the absolute value for negative magnetostrictive samples decreases while for positive magnetostrictive samples increases).

Correlation between Hall effect and magnetostriction in nanocrystalline Fe90Hf7B3 ribbons

Abstract Results concerning the Hall effect and saturation magnetostriction λs dependence on the annealing temperature of Fe90Hf7B3 ribbons prepared by melt-spinning technique are presented. As a consequence of the structural changes induced by heat treatments, the magnetoelastic and electric properties of these materials are changing. A strong decrease of the extraordinary Hall coefficient Rs and saturation magnetostriction λs after nanocrystallization was observed.

Stress dependence of sound velocity in Fe-based amorphous wires

The dependence of the longitudinal sound velocity on the bias magnetic field and tensile stress in Fe/sub 77.5/Si/sub 7.5/B/sub 15/ amorphous wires are presented, The measurements were made using the magnetostrictive delay line principle. The results show that changes in longitudinal sound velocity with bias magnetic field and tensile stress applied along the length of amorphous wires are strongly dependent on the thermal treatment. In the as-cast state, the change of the longitudinal sound velocity is negligible. There is a monotonic dependence of the sound velocity value on the tensile stress up to about 12 MPa. For about 16 MPa and 600 A/m tensile stress and bias magnetic field magnitude, respectively the saturation value of the longitudinal sound velocity is reached.

Tensile stress dependence of the sound velocity in Fe-rich amorphous wires

Abstract Experimental results concerning the dependence of the longitudinal sound velocity in Fe 77.5 Si 7.5 B 15 amorphous wires on the tensile stress applied along the length of the wire are reported. We tested Fe 77.5 Si 7.5 B 15 amorphous wires, 125 μm in diameter, in the as-cast state and after stress–relief process. The measurements were made using the magnetostrictive delay line principle. The obtained results show a strong dependence of the longitudinal sound velocity in the amorphous wire on the applied tensile stress. For a given value of the bias magnetic field, the longitudinal sound velocity increases with increasing the tensile stress value. For about 16 MPa tensile stress and 700 A/m bias magnetic field values, the saturation value of the longitudinal sound velocity is reached.

Stress dependence of saturation magnetostriction for glass-covered amorphous wires

In this paper, the aim is to analyse the influence of tensile stress (applied during treatment as well as during measurements) on /spl lambda/s value, for positive, negative and nearly zero magnetostrictive Fe/sub 72.5-x/Co/sub x/Si/sub 12.5/B/sub 15/ glass-covered amorphous wires. During treatments, the current density, tensile stress and annealing time values were varied up to 250 X 10/sup 6/A/m/sup 2/, 500 MPa and 250 minutes respectively. The amorphous state was examined by X-ray diffraction.

Corelation between Hall effect and magnetostriction in FeCuNbSiB ribbon

Nanocrystalline FeCuNbSiB alloys show excellent soft magnetic properties due to the ultrahe grains of a-FeSi phase embedded m a residual amorphous matrix. The stmctural phases formed in nanocrystalline Fe-based alloys lead to decrease of the saturation magnetostriction M e r nanocrystallization a very low coercive Beld, relatively high saturation magnetisation and an important increase ofthe initial permeability were obtained [1,2]. The aim of this paper is to analyse the Hall effect in amorphous and nanocrystalline FenFu,NbaSi&b ribbons. The obtained results are correlated with the magnetostriction behavior after annealing. The amolphous FeCuNbSiB ribbons were prepared by rapid solidification kom the melt 7be nanocqstaline structure in the amorphous ribbons was achieved by annealing at 4OOoC, 450°C. 5OO0C, 550°C, 575°C and 600T for 1 hour. The amorphous and nanocrystalline states of the samples were examined by X-ray d&action, ditferential thermal analysis (DTA) and thennomagnetic measurements. The Hall voltage measurements were performed at room temperature by the Van der Pauw method using external magnetic induction values up to 2T, Cu contact padswith silver paint soldered wires and dc sample biasing currents between 5 aod 50 mA [3,4]. Each value of the Hall voltage is the average of live measurements. The saturation magnetostriction of samples was determined using the small angle magnetization rotation ( S A M R ) method [5]. The analysed samples were 10 mm wide and 40 mm long. Figure 1 premts the dependence of the Hall voltage on the external magnetic induction applied during measurements for Fe73 J C U I % S ~ , ~ . ~ B ~ amorphous ribbons tested in the as-cast state for six sample biasing w e n t vahes(5,10,20,30,40,50 mA).