Maria Neagu

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.

Domain wall propagation in Fe-rich glass covered amorphous wires

Abstract The domain wall velocity in Fe77.5Si7.5B15 glass covered amorphous wires, before and after glass removal was determined. The domain wall axial velocity linearly increases with driving magnetic field. The driving magnetic field is higher for glass covered amorphous wires than for conventional ones having the same composition. The domain wall velocity increases when the diameter of the metallic core decreases and the critical field of reverse domain nucleation decreases with increasing the wire diameter. After glass removal, the nucleation and drive fields decrease.

A new magnetic field sensor based on magnetostrictive delay lines

A magnetic field sensor based on the dependence of the magnetostrictive delay line (MDL) response on its biasing magnetic field is presented in this paper. Such a sensor can be formed in an integrated array measuring the distribution of field along the MDL axis. Experimental results are reported for amorphous FeSiB wire MDLs, showing that high sensitivity and nonhysteresis are two advantages of this type of sensor.

Torsion and stress in amorphous positive magnetostrictive wires

In this paper we report some results on the dependence of the pulsed voltage output on the applied torsion or tensile stress in Fe/sub 77.5/Si/sub 7.5/B/sub 15/ amorphous wires used as magnetostrictive delay lines. The obtained results show a non monotonic dependence of the response of the delay line on applied torsion. For applied tensile stress the response could be fitted by a linear curve for as-cast wires and by an exponential curve for annealed wires. The good ratio between minimum and maximum magnetostrictive delay line signals and the absence of hysteresis suggest the possibility to use this technique in load cells and torque sensors.

Structural and Magnetic Properties of FeCuNbSiB Thin Films Deposited by HiPIMS

Using high-power impulse magnetron sputtering (HiPIMS) technique, Fe73.5Cu1Nb3Si15.5B7 thin films with thickness between 40 and 700 nm were deposited. The influence of deposition conditions (deposition time and argon pressure) and of the annealing temperature on the structure and coercive magnetic field of the magnetic films was analyzed. In the as-deposited state, the coercive magnetic field presents a minimum at about 10 mtorr argon pressure. The X-ray diffraction studies show that in the as-deposited state, the samples are amorphous, while after annealing at temperatures between 400°C to 525°C, α-Fe(Si) grains start to nucleate, the grain size varying from 2 to 18 nm. The Curie temperature of as-deposited amorphous phase and the onset of the primary crystallization are 355°C and 460°C, respectively. The lowest coercive magnetic field was obtained after annealing at 475°C.

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.

Effect of Mo and Nb additions on the magnetic properties of CoFeSiB amorphous wires

Abstract The effect of Mo and Nb addition on the magnetic properties of the Co 68.25−x Fe 4.5 Si 12.25 B 15 M x ( M = Mo , Nb ),(x=0,1,2,3) amorphous wires prepared by a rotating water quenching technique was investigated. It was found that the substitution of Co by Mo or Nb improved the wires glass-forming ability and thermal stability. The relative magnetic permeability also increased. The saturation magnetostriction changed its sign from nearly zero but negative to small positive.

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).

Sound velocity in Fe-rich glass covered amorphous wires

Abstract The bias magnetic field ( H ) dependence of the longitudinal sound velocity ( v ) in Fe 77.5 Si 7.5 B 15 glass covered amorphous wires is reported. The amorphous wires were tested in the as-cast state and after dc current annealing between 5 and 20 mA for 10–30 min. For the glass covered amorphous wires tested in the as-cast state the bias magnetic field dependence of the sound velocity was insignificant. For current annealed samples a decrease of the sound velocity for the smaller bias magnetic fields was observed. Increasing the annealing temperature, the bias magnetic field corresponding to the v minimum decreased. For about 600 A/m bias magnetic field, the longitudinal sound velocity reaches saturation.

Inverse Wiedemann Effect in glass-covered amorphous wires

Abstract We present results concerning the Inverse Wiedemann Effect (IWE) in Fe 77.5 Si 7.5 B 15 amorphous glass-covered wires having 10–27 μm and 5–15 μm diameters of the metallic core and thickness of the glass cover, respectively, and also on wires obtained after the glass removal. The dependence of the IWE voltage induced in the pick-up coil on torsion, tensile stress, and frequency of the ac current flowing through the wire are analysed. The amorphous wires were tested in the as-cast state and after heat treatments performed by current annealing technique, with and without applied torsion along the length of the wire. The obtained results show that the IWE voltage strongly depends on the state of amorphous wires (as-cast or annealed). The work was made in order to realise new sensor elements using glass-covered amorphous wires.