Fe-rich Wires Research Articles

Hysteresis Properties of Hexagonal Arrays of FePd Nanowires

FePd nanowires (NWs) with different compositions have been grown into anodized aluminum oxide templates (AAO) by AC electrodeposition at room temperature. The effects of nanowire composition and morphology on the hysteresis properties of the ordered array of NWs are investigated. All the NWs are polycrystalline; the Fe-rich wires have a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$bcc$</tex></formula> structure while the Pd rich ones are <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$fcc$</tex></formula> . FePd NWs are ferromagnetic and the spontaneous magnetization is found to be parallel to the nanowire long axis (out of plane easy axis) and both, the saturation polarization and the coercive field increase with the iron content.

Remagnetization Process of Fe-Rich Amorphous Wire Under Time Dependent Tensile Stress

An influence of a time dependent external tensile stress on the remagnetization process of a bistable wire is investigated experimentally and numerically. The dependence of the magnetization on the frequency of the tensile stress is analyzed in terms of the magnetic domain structure of Fe-rich wires. The dependence of the switching field on the phase of the tensile stress is presented and reproduced by a straightforward numerical simulation of the remagnetization process in a bistable wire. There, the input is the experimental static dependences of the switching field and of the magnetization of the wire on an external tensile stress. The presented dependences of the switching field and the magnetization on the periodic tensile stress allow to tune the shape of the hysteresis loop, what can be useful in constructing a phase sensor.

Fe-Rich Ferromagnetic Wires for Mechanical-Stress Self-Sensing Materials

The possibility of using Fe-rich wires in mechanical stress self-sensing materials is investigated. To this end, a retrieval technique aimed to characterize the high-frequency magneto-impedance effect in ferromagnetic wires under mechanical stresses is proposed. The technique is based on the measurement of the wires inside a metallic rectangular waveguide, and it is validated through numerical simulations and tested with already published experimental data. In addition, the studied Fe-rich wires are characterized by the occurrence of the natural ferromagnetic resonance, whose frequency position increases from 7 to 8.25 GHz for elongations ranging from 0 to 60 μm.

Influence of the Circular Magnetic Field and the External Stress on the Remagnetization Process in Fe-Rich Amorphous Wires

The remagnetization process of Fe-rich wires as dependent on the circular magnetic field induced by the AC current flowing through the wire is investigated experimentally. We present the dependence of the switching field on the amplitude and frequency of the circular magnetic field and its variance with the applied tensile stress. The results are interpreted in terms of magnetic domain structure of the wire.

Influence of magnetic field and torsional stress on the skin penetration depth of Finemet wires

The skin penetration depth of Fe-rich wires is obtained in this work, from the impedance measurements, as a function of applied magnetic field and torsional stress. The Fe 73.5Si 13.5B 9Nb 3Cu 1 wires have been submitted to different annealing treatments in order to get the softest magnetic behaviour in the nanocrystalline state. A decrease in electrical resistivity and improvement of the soft magnetic properties of the wire annealed at 565 °C is observed. Changes in skin penetration depth of up to 36 μm are achieved with a small torsion in the nanocrystallized wire. Results can be understood by the dependence of permeability on applied magnetic field and torsional stresses.

Fe-Rich Wires as Elements for Torsion Sensors Based in Torsion Impedance Effect

Fe-Rich Wires as Elements for Torsion Sensors Based in Torsion Impedance Effect

Magnetic and magnetotransport properties in thin Fe-rich wires processed by cold drawing

A study of microstructure (X-ray diffraction), magnetic properties (switching field associated with the magnetic bistability), and giant magnetoimpedance (GMI) effect in cold-drawn Fe77.5B15Si7.5 amorphous wire is presented. The initial amorphous wire (obtained by the in-rotating-water spinning technique) with a diameter of 125 μm was subjected to cold drawing to decrease the diameter to 50 μm. Such cold-drawn wire was subjected to current annealing for tailoring the magnetic and GMI properties.

The effect of different annealing treatments on magneto-impedance in Finemet wires

In this paper, we analyze the behaviour of Fe-rich wires that have been submitted to a current annealing, with and without an applied torsional stress. The structural relaxation and induced anisotropies achieved in the samples produce different effects in the magneto-impedance and torsion impedance response, in comparison with the as-quenched wire, due to the different domain structure and magnetization processes involved.

Distribution of switching field fluctuations in Fe-rich wires under tensile stress

We present experimental results on the influence of the applied tensile stress on switching-field distribution in as-cast Fe-rich amorphous wires. The fluctuation spectrum of the switching field reveals two different mechanisms, namely (i) magnetoelastic coupling of the domain wall with internal stresses, which significantly varies with the applied stress, and (ii) pinning of the domain wall at defects of the atomic scale.

Magnetic domain structure of wires studied by using the magneto-optical indicator film method

Experimental studies of the magnetic domain structure of amorphous wires with positive (Fe-rich) and negative (Co-rich) magnetostriction by using the magneto-optical indicator film method have been performed. The following main results have been obtained. (i) Fe-rich wires possess unclosed 180° surface domain structures with magnetization perpendicular to the wire surface, i.e., without closure domains previously assumed for such materials. Such results have been attributed to the large magnetolastic anisotropy induced by the fabrication process. (ii) Domain structures of Co-rich wires consist of rather big (as-compared with Fe-rich wires) circular domains.

Structural, magnetic and electrical transport properties in cold-drawn thin Fe-rich wires

Microstructural (X-ray diffraction), magnetic properties (hysteresis loop), electrical resistivity, magneto-impedance and stress impedance effects have been investigated in cold-drawn Fe 77.5B 15Si 7.5 amorphous wire. Initial amorphous wire (obtained by the in-rotating-water technique) with diameter of 125 μm was submitted to cold-drawn process decreasing the diameter to 50 μm. Such cold-drawn wire was treated by current annealing (currents of 190, 210, 220 and 230 mA during times between 1 and 45 min) for tailoring the magnetic and electrical transport properties. A qualitative analysis of the magnetoimpedance and stress impedance effects is given by considering the influence of the magnetoelastic anisotropy and frequency of the AC driving electrical current on the circular permeability.

Two magnetic phases in cold-drawn Fe-rich amorphous wire

Magnetic properties have been studied in ferromagnetic amorphous wires of nominal composition Fe 77.5B 15Si 7.5 and diameter 0.05 mm prepared by cold-drawing technique. Conventional and surface hysteresis loops were measured by fluxmetric method and by magneto-optical Kerr effect method, respectively. Saturation magnetization dependence with the current density has been obtained. Two Curie points were clearly distinguishable on this dependence that could be associated with the existence of two ferromagnetic phases. On the other hand, two successive jumps of magnetization have been observed in fluxmetric as well as in magneto-optical curves. The joint analysis of the bulk and surface hysteresis loops permits us to conclude that the cold-drawing post process induces strong helical anisotropy in the Fe-rich wires studied. The helical magnetic structure exists in the surface and, also, in the volume of the wire. We consider that the helical magnetic structure forms the separate magnetic phase that finds the reflection in the two Curie points behavior.

Tensile stress dependence of the magnetostatic interaction between Fe-rich wires

We study the influence of the applied tensile stress on the magnetostatic interaction between two amorphous Fe-rich wires. The hysteresis loop is measured for: (i) conventional wires produced by in-rotation-water method, with diameter of 125μm, (ii) cold-drawn wires with diameter of 50μm. The stress dependence of the interaction field is evaluated from the shape of the hysteresis loops, which show characteristic two-step behaviour. These steps mark the values of the switching field of the wires. For the conventional wires the tensile stress dependence of the interaction field can be explained as a result of the tensile stress dependence of the magnetization. For the cold-drawn wires, the interaction field shows a maximum with the applied stress. This behaviour is interpreted as a consequence of a local variation of the domain structure at the wire ends. It modifies the stray field, and—as a consequence—the switching field of the neighbouring wire.

Effect of the wire length on the torsion impedance in Fe-rich wires

Abstract In this work, we show the results of measuring the impedance as a function of the applied torsion on amorphous Fe73.5Si13.5B9Cu1Nb3 wires with a 133 μm diameter and lengths between 2 and 10 cm. A decrease of the impedance value can be observed as a consequence of the decrease of the wire length, and sensitivities to the applied torsion up to 57%/rad/cm can be measured at a drive current frequency of 2 MHz.

Torsional stress dependence of reactance and resistance in Fe-rich amorphous wires at low frequencies

Amorphous ferromagnetic wire with a highly positive saturation magnetostriction coefficient, made of Fe 73.5Si 13.5B 9Nb 3Cu 1, was simultaneously submitted to both, an AC current passing through it and a torsional stress, in order to induce a helical magnetic anisotropy in the wire that modifies its domain structure and therefore the magnetic response of the sample. The aim of this work is to study the reactive, resistive and impedance behaviour in this Fe-rich wire, submitted to different applied torsional stresses, and for several values of the AC current amplitude through the wire (5–20 mA rms), in the low frequency range, f<MHz. The experimental results are explained on the basis of the core-shell model.

Length effect in a Co-rich amorphous wire

The effect of the sample length on the magnetization process of a Co-rich amorphous wire has been experimentally and theoretically studied in this paper. Experimentally it is found that the spontaneous magnetic bistability observed in a Co-rich wire is lost if the sample becomes shorter than some critical length. Such critical length is smaller than that one of Fe-rich wire. Besides, the remanent magnetization of a wire with the length less than the critical length is an increasing function of the wire length. Theoretical explanation of the observed behavior suggests that the magnetization of the inner core of the Co-rich amorphous wire, normally directed along the wire axis, may be twisted near the wire ends due to the demagnetizing field. As a result, the longitudinal component of the wire magnetization reduces gradually towards the wire ends. It is shown that the characteristic critical length for the reduction of the longitudinal magnetization component can be several orders larger than the wire radius. This estimation is in qualitative agreement with the experimental data.

Torsion and stress effects and modelling in positive magnetostrictive wires

Results on torsional and tensile stress dependence in amorphous magnetostrictive Fe-rich wires used as magnetostrictive delay line are reported in this paper. The obtained results show a not monotonic dependence of the pulsed voltage output on the applied torsion along the length of the amorphous wire and a monotonic dependence for applied tensile stress. The dynamic modelling of the outer shell behaviour in positive magnetostrictive wires, under stress and torsion, is consequently analyzed.

Measurements of magnetization dynamics and magnetoimpedance in FeCoSiB and FeSiB amorphous wires

A technique to observe magnetization dynamics in amorphous wires is described. When an ac current passes through the amorphous wire, voltages induced between both ends of the wire and in a pickup coil wound around the wire are observed. These voltages indicate circumferential and axial components of magnetization changes in the wire, respectively. Observations in a Co-rich wire having slightly negative magnetostriction and an Fe-rich wire having positive magnetostriction under various bias fields showed quite different wave forms which indicate their domain structure.

Switching mechanism and domain structure of bistable amorphous wires

Hysteresis loops and domain structure of as-cast Fe-rich and stress-annealed low magnetostrictive Co-rich bistable wires have been investigated as functions of the distance to the end of wires with different lengths. From the analysis of the changes of the squareness ratio and differential susceptibility at remanence, the existence of conical closure domains at the ends to decrease the magnetostatic energy is inferred. The switching process is accompanied by a sudden reconstruction of the domain structure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magnetic Properties and Large Barkhausen Effect of FeCo, FeCr, FeNi System Amorphous Wires

Fe-rich and Co-rich amorphous magnetostrictive wires have shown sensitive bistable flux reversal (large Barkhausen effect or re-entrant flux reversal) characteristics. Fe-Co, Fe-Cr and Fe-Ni system amorphous wires were prepared, and their various magnetic properties (M s , M r /M s , K u , ? s , H*, and ? s M s /K u ) were measured to investigate the general properties of the large Barkhausen effect and stress sensitivity of such amorphous wire. A domain wall propagates through an inner core of diameter about 1/?2 times that of positive-magnetostriction wires, and about 1/?3 times that of negative-magnetostriction wires. The stress sensitivity of magnetization was analyzed using a figure of merit F defined as (3/2) ? s M s (1?(M r /M s )2) (M r /M s )/K u .