Glass-covered Wires Research Articles

Surface anisotropy and spin wave resonance in submicron amorphous wires

Abstract The influence of surface magnetic anisotropy on ferromagnetic resonance (FMR) in submicron wires is investigated both theoretically and experimentally. An analytical formula for resonance fields of radial spin waves in a long axially magnetized circular cylinder is obtained. Three types of surface anisotropy with the easy direction along one of the cylindrical coordinates are considered. For sufficiently strong surface anisotropy with hard direction parallel to the cylinder axis the surface spin wave mode is observed. The theoretical results are verified by FMR measurements at six microwave frequencies from 9 to 69 GHz on glass-covered amorphous FeCrSiB wires with diameters from 541 to 1032 nm. From the bulk spin wave resonances the exchange stiffness constant about 6.5 10−7 erg/cm is obtained. The frequency dependence of the surface mode resonance field indicates that a perpendicular surface anisotropy with anisotropy constant Ks = 6.2 erg/cm2 is present at the metal/glass interface.

Lifshitz topological impurity transitions in bismuth wires doped with acceptor and donor impurities

This paper reports the results of an experimental study of electronic topological transitions in bismuth glass-covered wires doped with acceptor (Sn) and donor (Te) impurities. The temperature dependences of the thermoelectric power and resistance are measured within the temperature range from 1.5 to 300 K and magnetic fields up to 14T. The position of the Fermi level eF and the concentration of charge carriers at doping are estimated from the Shubnikov de Haas (SdH) oscillations which are clearly visible from both L electrons and L and T holes in all crystallographic directions. We demonstrate anomalies in the temperature dependences of the thermopower in Bi wires doped with acceptor (Sn) and donor (Te) impurities in the form of a triple (doping by Sn) and double (doping by Te) change in the sign of the thermopower. The effect is interpreted with relation to the manifestation of impurity Lifshitz topological transitions. The SdH oscillation method was used to determine the energy position of the Σ band by doping Bi wires with the acceptor impurity Sn and the T band conduction by doping with Te. It is shown that the appearance of the Σ and T bands in Bi wires doped with the acceptor and donor impurities is responsible for the anomalies in the diffusive thermoelectric power, which gives a good conform with to the theoretical models and predictions.

Thermal Stability of Giant Magneto-impedance Effect in Glass-covered Amorphous Wires

Abstract Thermal stability of Giant magneto-impedance (GMI) effect of Co-based amorphous glass-covered wires was investigated. The temperature measurement was conducted in a special calorstat cell between 25 °C and 200 °C, and the GMI effect of the as-cast, glass-removed and DC annealed wires was measured at 100kHz-12 MHz ranging from 0 Oe to 80 Oe. Experimental results show that the ambient temperature has a significant influence on the thermal stability of GMI effect, it is caused by external conditions: driving frequency, magnetic field and sample states. The thermal stability and GMI fluctuating variation at different temperature of three-type wires could be quantificationally characterized by GMI max ratio variation difference Δ[ΔZ/Z max ] T max of three-type wires, and drastically improved with the driving frequency increasing to 10 MHz, and the working range of magnetic field for possible sensor applications should be below 10 Oe. While there is different from as-cast and glass-removed wires, DC annealed wire has twin-working-zone range (relatively low field 0 Oe-2 Oe & relatively high field 2Oe-10 Oe) of magnetic field at relatively high frequency (10 MHz) for sensor applications with different detection range of weak magnetic field. So, the improved thermal stability is caused by the co- actions of remarkable skin-effect, magnetic polarization and magneto-crystalline anisotropy energy with the increasing frequency. It therefore is concluded that the optimal driving frequency of 10 MHz and the detection range of weak magnetic field (2Oe-10 Oe) is favorable for the design parameters choices of high-performance GMI sensor.

Noise Suppression Effect of Composites Containing Glass-Covered Amorphous CoFeSiBCr Wires

The noise suppression effect and its mechanism are investigated for a composite sheet and a composite film made of glass-covered amorphous CoFeSiBCr wires. Both samples show a significant noise suppression effect. The power loss ratio of the composite sheet is above 80% from 1.6 GHz to 8.5 GHz, and that of the composite film is above 70% from 3.2 GHz to 8.5 GHz even if its thickness is only 0.20 mm. The composite sheet demonstrates high real and imaginary permittivity above 30.7 and low real and imaginary permeability below 1.2. The surface resistivities of the two composite samples are as high as about 3×1012Ω/square. The power loss of the composite containing glass-covered wires should be mainly contributed by dielectric loss derived from electronic polarization and relaxation.

Study of Stress Annealing on Giant Magneto-Impedance in Glass-Covered Co-Based Amorphous Microwires

The glass-covered Co-rich amorphous wires was annealed by an applied stress during the current annealing process. The influence of stress and dc current annealing on the giant magneto-impedance (GMI) effect were investigated by the magneto-impedance. Our experiments showed that the magentic anisotropy is reduced by the annealing treatments, furthermore, the maximum GMI value is increased to 105 %.The GMI value is enhanced by increasing the outer domain volume and inducing a transverse anisotropy due to the changing of inner stress.

Influence of Frequency and Bias Current on Asymmetrical GMI Effect in Co71.8Fe4.9Nb0.8Si7.5B15 Amorphous Glass-Covered Wires

The Co71.8Fe4.9Nb0.8Si7.5B15 amorphous glass-covered wires (AGCW) are prepared by the Taylor-Ulitovsky technique. The frequency dependence of asymmetrical giant magneto-impedance (AGMI) effect in amorphous glass-covered wires annealed by 70 mA DC current is here presented. The resistance R and the reactance X have been measured, respectively. The real part R and the imaginary part X of impedance play an important role at high frequency and low frequency, respectively. The influence of DC bias current from Ib = 0 mA to Ib = 5 mA at 30 MHz on the GMI effect in the glass-covered wires annealed by 70 mA DC current is investigated. The asymmetry becomes the largest around Ib=1 mA, and finally decreases for the larger bias current Ib=5 mA. The maximum ΔZ/Z ratio of 310% is observed at 58 MHz under 1 mA bias current.

Effect of glass removal on the GMI effect of Co 71.8Fe 4.9Nb 0.8Si 7.5B 15 amorphous glass-covered wires

During the past several years, giant magneto-impedance effect (GMI) in amorphous wires has generated growing interest in the science community because of their applications in sensors. The giant magneto-impedance effect in Co 71.8Fe 4.9Nb 0.8Si 7.5B15 amorphous glass-covered wires (AGCW) consists of strong changes in the high frequency impedance with a small DC magnetic field. When f = 1 MHz, there is no GMI effect due to the fact that the magnetic penetration depth is higher than their radius. As the frequency increases, the GMI effect becomes important in both the glass-covered wire and the wire after glass removal. Field dependence of the impedance has a similar behaviour to the AGGW ones, when a tensile stress is applied to the wire without glass cover.

Giant Stress-Impedance Effect in Co71.8Fe4.9Nb0.8Si7.5B15 Glass-Covered Amorphous Wires

The giant stress-impedance (GSI) effect in as-cast and DC current annealed Co71.8Fe4.9 Nb0.8Si7.5 B15 amorphous glass-covered wires is presented. The SI ratio of the as-cast sample exhibits negative GSI effect. For the sample annealed by 60 mA DC current, the SI ratio first increases with applied tensile stress, then decreases. The maximum ΔZ/Z ratio of 304% is obtained. Frequency dependence in the range from 1 to 110 MHz of the GSI effect is investigated. Experimental results show that the real part R and the imaginary part X of impedance play an important role at high frequency and low frequency, respectively. At 1 MHz, the maximum ΔX/X ratio of 1 448% is obtained. At 110 MHz, the maximum ΔR/R ratio of 648% is obtained.

Noise sources in miniature fluxgate sensors. Part II: the case of sensors with Fe77.5Si7.5B15 amorphous wire cores

As a continuation of Part I this paper is devoted to fluxgate sensors that employ Fe77.5Si7.5B15 amorphous wires as magnetic cores, with attention being paid to fluxgate miniaturization. Two types of fluxgate sensors have been constructed. The first type is based on the high axial anisotropy exhibited by amorphous wires and employs two coils, an excitation and a receiving one. The second type employs the large Matteucci effect, owed to helical anisotropy induced into such wires either by mounting under torsion or by torsion annealing. The latter fluxgate type employs one single excitation coil. The exploitation of the Matteucci effect indicates that it may lead to the construction of miniature fluxgate sensors. The voltage-output of a series of such sensors has been sampled and processed. The repeatability of the flux-reversal process in the presence of helical or axial anisotropy is quantitative and qualitative investigated to allow for understanding the nature of noise. The existence of noise-sources that have been modeled in Part I is investigated and their power spectral density is estimated, from the experimental results. The influence of several manufacturing parameters in the noise at the output of fluxgates sensors is experimentally verified. Such parameters are the dimensions of the core, the presence and thickness of the glass-cover in glass-covered wires, the level of applied stress and torsion, working temperature level, and the characteristics of the excitation waveform. An irregular behavior at the hysteresis loop of fluxgates that employ the Matteucci effect is observed, which could be understood as a kind of perming effect. Measurements of the repeatability and hysteresis errors, of the sensors transfer function (output-voltage vs input-field), are presented, along with measurements of the cross-field sensitivity. The latter errors do not count as noise, but may limit the performance of fluxgates significantly, especially when miniaturization is attempted. Finally some design rules and manufacturing hints are proposed for fluxgate-magnetometer noise reduction.

Diameter influence on magnetoimpedance of Co-based glass-covered amorphous wires

The aim of this work is to show the dependence on geometrical parameters of magnetoimpedance (MI) of amorphous wires. The samples used are Co-based glass-covered amorphous wires with metallic diameter of about 0.055, 0.100 and 0.150 mm and total diameter of 0.065, 0.130 and 0.200 mm, respectively. A decrease in the MI ratio is observed when the diameter decreases due to the skin effect as a consequence of the higher ratio between diameter and penetration depth. It is also important to note that the maximum observed value of MI ratio is displaced to higher frequencies when the diameter of the sample is reduced.

The influence of the composition on the GMI effect in low magnetostrictive amorphous microwires

Abstract The influence of the composition on both the magnetostriction and the GMI effect in Co 72.5− x Fe x Si 12.5 B 15 ( x =5.5–6.2) amorphous glass-covered wires is investigated. The basic magnetic properties of these materials as well as internal stresses induced by the glass cover during the preparation process strongly influence the GMI effect.

Magnetoelastic uniformity of glass-covered wires used in magnetostrictive delay lines

This paper presents experimental results concerning the possibility of using glass-covered amorphous wires (GCAW) as magnetostrictive delay lines (MDL). High frequency current annealing, heat annealing and dc current annealing are used in order to make the magnetic and magnetoelastic response of glass-covered amorphous wires as uniform as possible.

FMR Investigation of the amorphous CoFeSiB glass-covered wires in the presence of mechanical tension

Abstract Results on the FMR investigation of the effect of applied tensile stresses on the surface magnetic anisotropy of Co68.25Fe4.5Si12.25B15 amorphous glass-covered wires are reported. Axial stresses determine a decrease of the resonance field and an increase of the absorption intensity that correspond to the resonance peak, indicating a reinforcement of the circumferential magnetoelastic anisotropy from the wire's surface region.

High-frequency magnetic aftereffect in Co-based amorphous wires and ribbons

In this work, the magnetoimpedance relaxation in Co 68.25Fe 4.5Si 12.25B 15 systems has been measured in the frequency interval 500 kHz–3 GHz. A comparison between ribbons, amorphous and glass-covered wires of nominal composition Co 68.25Fe 4.5Si 12.25B 15 was made. The time variation of the calculated characteristic impedance after field removal displays a similar behavior to the classic magnetic permeability aftereffect measured at lower frequencies by means of conventional fluxmetric techniques. Thermal treatments are shown to affect the impedance relaxations in melt-spun alloys. Conversely, no substantial effect has been observed in glass-covered wires.

Magnetoelastic behavior 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).

Magneto-impedance measurements in amorphous Co-based magnetic wires at high frequency

An alternative method to evaluate the magnetic response of soft magnetic systems in the high-frequency region (1 MHz–6 GHz) is presented here. The proposed experimental set-up is based on the measurement of the four scattering parameters S ij of a coaxial line by means of a vectorial network analyzer. The magnetic sample, either in wire or ribbon form, is used as the inner conductor of a coaxial line. The characteristic impedance of the line section is given by an analytical formula taking into account the geometrical structure of the device and the sample physical properties. Transmission line theory has been successfully employed to extract from the raw experimental data the information concerning the magnetic sample, discarding the contribution of the terminations. Magneto-impedance is obtained by measuring the characteristic impedance under different applied magnetic fields. The proposed method provides a natural extension of the usual characterisation techniques from lower frequencies up to 6 GHz. As an example, the magneto-impedance response of Co-based amorphous and glass-covered wires in the high-frequency region will be discussed.

Magnetic properties of amorphous glass-covered wires

Magnetic properties of ferromagnetic amorphous glass-covered wires with positive, negative, and nearly zero magnetostriction are reviewed. It is shown that their peculiar magnetic characteristics originate during the specific preparation process through dimensions and induced internal stresses. The role of the magnetoelastic coupling on the domain structure formation and subsequently on the magnetization process is discussed, together with the tailoring possibilities of such magnetic materials.

FMR investigation of the amorphous CoFeSiB glass-covered wires in the presence of mechanical tension

Results on the FMR investigation of the effect of applied tensile stresses on the surface magnetic anisotropy of Co 68.25Fe 4.5Si 12.25B 15 amorphous glass-covered wires are reported. Axial stresses determine a decrease of the resonance field and an increase of the absorption intensity that correspond to the resonance peak, indicating a reinforcement of the circumferential magnetoelastic anisotropy from the wire's surface region.

Amorphous and nanocrystalline glass-covered wires

Important scientific goals of far-infrared and submillimetre astronomy include measurements of anisotropies in the cosmic background radiation, deep imaging surveys for detection of high-red-shift galaxies, and imaging and spectroscopy of star formation regions and the interstellar medium in the milky way and nearby galaxies. Use of sensitive bolometer arrays leads to very large improvements in observing speed. Recent progress in the development of bolometric detector systems for ground-based and space-borne far-infrared and submillimetre astronomical observations is reviewed, including spider-web NTD bolometers, transition-edge superconducting sensors, and micromachined planar arrays of ion-implanted silicon bolometers. Future arrays may be based on planar absorbers without feedhorns, which offer potential advantages including more efficient use of space in the focal plane and improved instantaneous sampling of the telescope point spread function, but present challenges in suppression of stray light and RF interference. FIRST and Planck Surveyor are planned satellite missions involving passively cooled (∼70 K) telescopes, and bolometer array developments for these missions are described.

Comparison between magneto-impedance properties of Fe 73.5Cu 3Nb 1Si 13.5B 9 melt-spun and glass-covered wires

A comparison between magneto-impedance properties measured in magneto-strictive nanocrystalline Fe-based melt-spun and glass-covered wires is presented as a function of microstructure. Giant magneto-impedance response has been investigated in both low- and high-frequency regions for different thermal treatments. A strong correlation with the domain structure, affected by the microstructure of the material, has been observed. Glass-covered wires turn out to be characterised by higher GMI values at all the studied frequencies with respect to rapidly solidified wires.