Nanocrystalline Wires Research Articles

ECR plasma assisted deposition of zinc nanowires

Deposits of one dimensional nanowires of zinc with diameters of 90–120 nm have been obtained by means of dc sputtering within an electron cyclotron resonance plasma reactor. The sputtering has been made effective by using a negatively biased cylindrical target. The structure of the nanocrystalline wires deposited on glass substrates were investigated with scanning electron microscopy, transmission electron microscopy and scanning tunneling microscopy. STM revealed that the structure of the one dimensional nanowires are ensemble of nanoclusters and nanowires with diameter of 4–5 nm. The crystalline nature of the metallic nanowires was studied with X-ray and electron diffraction analysis. The native oxide present on the metallic wires was revealed by photoluminescent spectroscopy. Theoretical modeling has been used to explain the possible mechanisms operative inside the plasma which lead into deposition of zinc on the substrate starting from the precursor species.

Soft magnetic properties, magnetoimpedance and torsion-impedance effects in amorphous and nanocrystalline FINEMET alloys: Comparison between ribbons and wires

A comparative study on the magnetoimpedance (MI) and torsion-impedance (TI) effects between Fe73.5Si13.5B9Nb3Cu1 FINEMET ribbons and wires has been performed. The samples were annealed for 1 h at temperatures below and above their primary crystallization temperature, around 520°C. The magnetic softening of the samples occurs during the nanocrystallization process, which enhances both the MI and TI effects up to 82% and 75%, respectively, in the wire sample, with respect to its as-quenched state. A maximum MI ratio of 50% is obtained in the nanocrystalline ribbon. The modified values of saturation magnetization, coercive field and magnetostriction, and changes in the domain structure improve the impedance response of the nanocrystalline wire for its use as a sensor element for detecting small magnetic fields, with a sensitivity of 17%/Oe and torsional stresses with a sensitivity of 700% rad/cm.

Circular magnetization process of nanocrystalline wires as deduced from impedance measurements

The circular magnetization process of FeSiBCuNb amorphous and nanocrystalline wires has been followed by the impedance measurements as a function of the amplitude and the frequency of driving current. The domain structure and consequently, the magnetization process have been tailored by suitable thermal processing. The different circular coercivity mechanisms are deduced by analyzing the magnetic losses. We find that the coercivity is due to domain-wall pinning for wire with axial domain, while the coercivity is from domain nucleation for one with transverse domain structure. In addition, the influence of axially applied field H is different for wires with different domain structure. The application of tensile stress to a wire with positive magnetostriction can be taken as an axial induced anisotropy, which makes the circular permeability decrease and the coercivity increase. Finally, the influence of driving current frequency on the circular magnetization process has been also studied for the wire with transverse domain structure. The results indicate that the frequency effect is from the eddy-current damping.

A novel method determining longitudinally induced magnetic anisotropy in amorphous and nanocrystalline soft materials

In ferromagnetic amorphous and nanocrystalline soft magnetic alloys the induced magnetic anisotropy plays a fundamental role in the hysteresis behavior but, due to the elongated shape, it can be measured only if KU is perpendicular to the sample long axis. In order to measure the longitudinal induced anisotropy, an original method derived from known thin layers measurement techniques was used. Hysteresis loops shifted by perpendicular bias field were recorded for this purpose. Direct measurement of the longitudinal induced anisotropy in amorphous and nanocrystalline ribbons or wire without needing sample preparation is reported for the first time. Evidence of self-induced anisotropy is brought in a Fe–Co-based nanocrystalline alloy.

Influence of Cr substitution in the magnetoimpedance response of FeSiBCuNb wires

A comparative study of the influence of Cr addition in the magnetoimpedance effect of Fe73.5−xCrxSi13.5Cu1B9Nb3 (x=0, 3, 7, 10) nanocrystalline wires is here presented. The devitrification of the initial amorphous structure of the samples gives rise to the typical nanocrystalline structure composed of Fe-rich nanograins surrounded by the residual amorphous matrix. The decrease in the Curie temperature of the residual matrix with the Cr content of the alloy below room temperature in the Cr richest compositions (x=7 and 10), has associated a magnetic hardening at room temperature, and thus a negligible magnetoimpedance contribution. However, samples with x=0 and 3 present similar magnetoimpedance ratios, characterized by huge changes of inductance (≈500%) with field at low frequencies (inductive effect). The inclusion of Cr can be very important regarding the applicability of these alloys, due the associated improvement in the corrosion resistance of the samples.

Anomalous enhancement of eddy-current anomaly factor in very soft ferromagnetic wires

The circular permeability, μ= μ′−j μ″, of two very soft ferromagnetic wires (Co 68.2Fe 4.3Si 12.5B 15 amorphous wire S1 and Fe 73.5Cu 1Nb 3Si 13.5B 9 nanocrystalline wire S2) has been determined from the measurements of the impedance, Z= R+j ωL, as a function of frequency ( f=0.1−100 kHz) and DC bias field ( H=0−89 kA/m). The axial field-dependent DC circular permeability, μ DC( H), of two samples exhibit the anomalous enhancement phenomenon as we observed in the similar samples before. The change of the low- f eddy-current anomaly factor, η, with H has been studied. With increasing H from 0 to 3600 A/m, η increase from 1.4 to 8.5 and from 2.8 to 4.2 for samples S1 and S2, respectively, which is contrary to the theoretical expectation that η( H) approaches the value of η=1 with the sample being saturated. This anomalous behavior of η( H) is analyzed in terms of the micro-domain structure resulted from magneto-static interaction between the magnetically hard inclusions and the soft matrix.

Torsion-dependent magnetoimpedance in FeCuNbSiB nanocrystalline wires with vanishing or transverse anisotropy

Two pieces of Fe73.5 Cu1 Nb3 Si13.5 B9 amorphous wires were submitted to thermal treatment without (S1) or under (S2) applied tensile stress, so inducing nanocrystalline structure characterized by two different types of magnetic anisotropy. Sample S1 exhibits longitudinal domain structure with small anisotropy constant, while a transverse domain structure with large transverse anisotropy is induced by stress annealing for sample S2. The specific magnetoimpedance response of each nanocrystalline wire has been studied as a function of the applied torsion, ξ. Both samples show the giant magnetoimpedance (GMI) effect, with GMI ratios of 190% and 145% at ξ=0 for wires S1 and S2, respectively. Applied torsion modifies the form as well as the amplitude of magnetoimpedance, which is discussed in terms of the competition between the magnetoelastic anisotropy induced by the processing and the helical anisotropy induced by the torsion. The torsion impedance has been modeled for the case of sample S1 under large enough helical anisotropy. The observed giant torsion-impedance effect of 320% and 235% for samples S1 and S2, respectively, is proposed to be employed in magnetoelastic torsion sensors. The use of the GMI effect is further emphasized to be a powerful tool to explore the magnetic structure and the magnetic anisotropy.

Giant magnetoimpedance effect in soft magnetic wire families

New results on the giant magnetoimpedance effect in soft magnetic amorphous and nanocrystalline wires and microwires are presented. The relation between the magnitude of the effect and the dynamic surface magnetization processes is analyzed. The special role of magnetostriction is discussed with a special emphasis on the possibilities it offers for improving the magnetoimpedance response of wire-shaped materials.

Giant magnetoimpedance effect and magnetoelastic properties in stress-annealed FeCuNbSiB nanocrystalline wire

Stress-current annealing performed on Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 13.5/B/sub 9/ amorphous wire results in ultra-soft nanocrystalline wire with an additional very homogeneous transverse magnetic anisotropy. The giant magnetoimpedance (GMI) response of this treated wire has been investigated in a range of ac current (I/sub ac/ = 0.2 to 20 mA) and frequency (f = 0.01 to 1 MHz). A maximum GMI ratio as high as around 150% is reported. The magnetoelastic behavior and in particular the influence of applied tensile and torsional stresses, has been analyzed in connection with GMI. From the applied stress dependence of the static field H/sub m/ at which the maximum impedance is observed, the values of induced anisotropy field (H/sub ind/ = 3.46 and 3.14 kA/m) and magnetostriction (/spl lambda//sub s/ = 1.42 and 1.59 /spl times/ 10/sup -6/) are determined.

GMI effect of Fe 73.5− xCr xCu 1Nb 3Si 13.5B 9 amorphous and nanocrystalline soft wires

Giant magneto-impedance, GMI, effect of Fe 73.5− x Cr x Cu 1Nb 3Si 13.5B 9 ( x=0 and 10) amorphous and nanocrystalline soft wires has been measured at the frequency range from 0.005 up to 5 MHz as a function of the varying DC axial field up to ±140 Oe. Thermal treatments (in conventional furnace and by current annealing, with and without applied stress) lead to partial devitrification and induced anisotropies; hence they exhibit enhanced soft magnetic behavior and modify the GMI response. The results obtained in the current-annealed samples, improved in comparison with those for samples annealed in furnace, are ascribed to the homogeneous structure as well as to the induced helical anisotropy. The influence of the sample length (1–8 cm long) on GMI as well as that of the induced anisotropies is analyzed considering the particular c-domain structure and magnetization processes of the wire.

Effects of magnetostatic interaction on the magnetization processes inFe73.5Cu1Nb3Si13.5B9 nanocrystalline wires

Fe73.5Cu1Nb3Si13.5B9 amorphous wire was annealedat different temperatures (Ta = 400-700C°, for 30 min)that result in partial devitrification and subsequently, the quasi-saturated hysteresisloop was measured. It is found that the loops are not symmetric, exhibitingtwo coercive fields, Hc1 and Hc2, on descending and ascendingbranches, respectively. Moreover, the asymmetry degree is modified whenthe sample is previously magnetized under a field of 60 kA m-1. Thedependence on both maximum measured field, Hm, and temperature,T, of the displaced loop has been determined. With increasing Hm,the shift Hsh = (Hc2 + Hc1)/2 decreases and the coercivityHc = (Hc2-Hc1)/2 increases, but Hsh-Hc = Hc1 remainsconstant. Both Hsh and the magnetic polarization,µ0Mm, at maximum field decreases with elevating T.The loop of this sample also shows a remarkable time-effect.The Hm- and T-dependent Hsh is discussed consideringthe existence of an effective bias-field generated from themagnetostatic interaction between the nanocrystalline particlesand residual soft matrix, and the time-effect could be ascribed tothe dipolar interaction among the particles.

AC field induced rotation of magnetostrictive wires

Under the excitation of high-frequency AC longitudinal magnetic field, a rotation can be induced in a magnetic wire under particular circumstances. In the present work latest results on amorphous, nanocrystalline and polycrystalline wires are reported. In particular, it is concluded that a minimum magnetostriction value is required to observe such an effect, irrespective of the structural nature of the wire.

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.

Magneto-Impedance Effect in Amorphous and Nanocrystalline Glass-Covered Wires

We report results on the magneto-impedance effect in Fe73.5Cu1Nb3Si13.5B9 nanocrystalline glass-covered wires, Co68.15Fe4.35Si12.5B15 amorphous wires, and in such wires after glass removal. The results are compared with those obtained for cold drawn and then tension annealed Co68.15Fe4.35Si12.5B15 amorphous wires. The magneto-impedance response of nanocrystalline wires after glass removal is larger than that of CoFeSiB amorphous wires after glass removal, being almost equal to that of cold drawn CoFeSiB amorphous wires. The results are explained in terms of specific domain structures and magnetic properties of the discussed wires, and they reveal the importance of good soft magnetic properties in a large magneto-impedance effect.

Applications of Amorphous and Nanocrystalline Magnetic Materials as Sensing Elements

The phenomena shown by nanocrystalline and amorphous ferromagnetic wires and ribbons, known as large Barkhausen jump, giant magnetoimpedance, Matteucci and inverse Wiedemann effect are described and analysed. The physical processes and mechanisms underlying these effects are thoroughly reviewed. Particular interest is finally focused on their applications in magnetic devices. These applications are mainly related to sensing and encoding systems.

Giant magneto-impedance effects in nanocrystalline soft magnetic alloy ribbons

SINCE the discovery of the giant magneto-impedance (GMI) effects in amorphous wire (or rib-bon) of CoFeSiB and nanocrystalline wire (or film) of FeCuNbSiB, it has attracted greatattention due to its promising potential applications in industry. Amorphous (and nanocrys-talline) soft magnetic alloys have very large magnetic permeability, when an ac driving currentand an external magnetic field (EMF) are applied, the EMF will damp the magnetic fluxchange caused by the ac driving current, thus the magnetic permeability will decrease; as a re-...

Fractographic Details of Directiy Cast Amorphous and Nanocrystalline Alloy Wire/ Fraktographische Untersuchung von Drähten aus direkt gegossenen amorphen und nanokristallinen Legierungen

The fracture surfaces of metallic glass wire and nanocrystalline wire were examined by scanning electron microscopy. Metallic glass wire failed in tension under ultra high stress and the surface morphology consists of a smooth and a veined region, evident of failure initiated by a shear mechanism followed by localised melting in the viscinity of the shear. Fracture morphologies of the nanocrystalline wire and glassy wire fractured in bend fatigue reveal features similar to those of classical brittle failure in glasses, showing features of mirror, mist, hackle and branching pattern. The dimensions of these patterns were used to estimate fracture properties of the wire samples.