Fe-based Amorphous Wires Research Articles

Catalytic properties of Fe-based amorphous alloys with different Mo content after acid corrosion

A series of Fe-based amorphous alloy wires with good formation ability, good flexibility, and a large specific surface area were prepared by the melt quenching method, which can be directly used as a self-supporting electrode for the oxygen evolution reaction (OER) of water electrolysis. By controlling the content of Mo, (Fe0.8Ni0.2)71Mo5P12C10B2 (Mo5), (Fe0.8Ni0.2)71Mo10P12C5B2 (Mo10) and (Fe0.8Ni0.2)71Mo15P10C2B2 (Mo15) alloy wires were prepared. It was found that Mo5 and Mo10 alloys still exhibit a fully amorphous structure, while the main body of Mo15 alloy comprises B2Fe3Ni3 and Mo6Ni6C phases. The electrochemical results showed that Mo15 alloy had the best intrinsic catalytic activity. The OER electrocatalytic performance of Mo15 was further improved by 1 h chemical etching after soaking in 0.5 M HNO3, which showed the overpotential was 239 mV and the Tafel slope was 40.6 mV/dec in 1 M KOH with a current density of 10 mA/cm2.

Fe-based amorphous alloy wire as highly efficient and stable electrocatalyst for oxygen evolution reaction of water splitting

The slow kinetics of the oxygen evolution reaction (OER) leads to low energy conversion efficiency during water electrolysis, thus it is very important to develop efficient and economical electrocatalysts. With high surface energy and rich active centers, amorphous alloys show excellent potential as self-supporting oxygen evolution catalysts for water splitting. In this work, (Fe0.8Ni0.2)71Mo5P12C10B2 amorphous alloy wire was successfully prepared, and after 5 h immersed in 0.5 mol/L HNO3, the wire surface was covered by the block metallic oxide. At a current density of 10 mA/cm2 in an alkaline electrolyte, the electrochemical results show that the overpotential is only 254 mV and the Tafel slope is 49 mV/dec. After the 194 h stability test, its oxygen evolution performance is even comparable to the commercial RuO2, which has been proven to have excellent electrochemical stability and low preparation cost. The highly efficient catalytic performance mainly originated from the synergistic effect of multi-metal elements and the unique crack surface characteristics which expose more active sites. This work provides new insight into low-metal-cost materials for efficient and durable OER electrocatalysts and their industrial applications in the future.

Observation of Magnetic Domains in Amorphous Magnetic Wires with a Diameter of 10 μm Used in GSR Sensors.

The core of a Gigahertz Spin Rotation (GSR) sensor, a compact and highly sensitive magnetic sensor, is composed of Co-Fe-based amorphous magnetic wire with a diameter of 10 μm. Observations of the magnetic domain structure showed that this magnetic wire has unusual magnetic noise characteristics. Bamboo-shaped magnetic domains a few hundred micrometers in width were observed to form inside the wire, and smaller domains a few micrometers across were observed to form inside these larger domains. The magnetic domain pattern changed abruptly when an external magnetic field was applied to the wire. Herein is shown how these changes may be a source of magnetic noise in the wire.

Effect of Coating and Annealing on Giant Magneto Impedance in Co and Fe-Based Amorphous Wires

Effect of coating with different chemical complexes on giant magneto impedance effect (GMI) was experimentally investigated in Fe and Co-based amorphous wires. The successive ionic layer adsorption and reaction (SILAR) technique was used for coating of the samples at room temperature. The SILAR method mainly based on adsorption and reaction on the ions from the solution and rinsing. Co and Fe-based amorphous wires were coated with CoO, asphaltene and ZnO chemical complexes. The coating thickness was determined to be about 1 μm thick. Maximum GMI ratio for Co and Fe-based samples were measured at 4 MHz and 5 MHz frequency, respectively. Influence of annealing at different temperatures on GMI effect was also experimentally investigated in the same samples. The coated samples were annealed at 300 C, 400 C, 500 C and 600 C temperatures in order to stress relief for 30 minutes. It is observed that the GMI ratio on Co- and Fe-based ZnO coated samples was highest at 500 ºC, while it was maximum on CoO coated Co-based samples at 400 ºC and on CoO coated Fe-based samples at 500 ºC. The highest GMI ratio among the measured samples was detected as 216 on the Fe-based, ZnO coated and annealed sample at 500 ºC at 5 MHz, while the smallest GMI ratio, was found to be as 88 on Co-based as-cast sample at 4 MHz. The measurements show that the GMI ratio is a combined effect of coating, annealing and frequency of ac current in a static magnetic field. Keywords Amorphous magnetic materials, SILAR technique, giant magneto impedance. Special Issue of Educational Sciences DOI: 10.7176/JSTR/6-06-03

Magnetic and Microwave Properties of Carbon-Coated Co- and Fe-Based Amorphous Wires

Rapidly quenched (Co0.94Fe0.06)72.5Si12.5B15 and Fe 75Si10B15 wires, 6 mm in length, are compared before and after low-temperature surface condensation of carbon. Energy-dispersive X-ray spectroscopy indicates a change in surface morphology and elemental composition, which affects the initial quenching stress distribution in the near-surface atomic layers. A comparative analysis of microwave properties over a frequency range from 0.05 GHz to 10 GHz before and after surface modification suggests a decrease of the dispersion of the local magnetic anisotropy axes.

Influence of Organic Coating on the Giant Magneto Impedance Characteristics of Fe-Rich Amorphous Wire

Influence of organic coating on the giant mag- neto impedance effect was experimentally investigated in Zn complex-coated dielectric Fe-based amorphous wires and optimized the giant magneto impedance (GMI) effect using artificial neural networks and MATLAB. A three- node input layer, a one-node output layer and three hidden layers with 21 neurons and full connectivity between nodes were developed with the transfer functions hyperbolic tan- gent in hidden layers and sigmoid in output layer. The input parameters were frequency, static magnetic field and sample type, while the output parameter was the giant mag- neto impedance effect. When the network performance was tested using untrained sample data, the average correla- tion and prediction error of giant magneto impedance effect were found to be 99 and 0.4 %. An analytical equation as depending on experimental data has been determined by using MATLAB Curve Fitting Toolbox™for giant mag- neto impedance. The square of the correlation and the root meansquared error were found to be 99 % and 0.89 respec- tively. The models including the different kinds of samples prepared have a good prediction capability and agreement with experimental results.

Hysteresis Loops of Soft and Hard Magnetic Composited Wires

Samples composed of soft and hard magnetic alloys were tailored by two steps annealing the same Fe-based amorphous wires. Then the measurements of hysteresisμ0Mloop have been performed upon the samples. The evolutions of loops with the fraction of hard magnetic phase and the measured magnetic field indicated the existence of dipolar interaction between the two phases.

Mechanical properties of magnetic Fe‐based and Co‐based amorphous wires and microwires

AbstractIn this paper we present measurements of the mechanical properties of magnetically soft Fe‐based and Co‐based conventional amorphous wires (CAW) and glass‐covered amorphous microwires (GCAW) in the as‐quenched state, before and after cold rolling, and after annealing for internal stresses relief. The tensile strength (σ) varies between 2000 MPa and 3400 MPa, strongly depending on CAW diameter and annealing temperature. The Young modulus (E) is following a descendant trend, decreasing with the diameter decrease. The increase of tensile strength (σ) and elongation (ε) values after cold‐rolling and post‐annealing is caused by the release of the internal stresses induced during the preparation. Tensile strengths up to 3900 MPa are achieved for Fe‐based GCAW, depending very strongly on the microwires diameter, but mostly on the glass cover thickness. σ reaches the maximum value of 3150 MPa for a Co‐based microwire having the glass cover of 9 μm and the total diameter of 43 μm, but increases even more after the glass removal (3350 MPa). This behaviour is attributed to the structural disorder and the specific magnetic domains structure in Fe‐based and Co‐based CAW and GCAW. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetostatic properties of amorphous and nanostructured Fe73.5Si13.5B9Cu1Nb3 wires

We present the results of experimental investigations of magnetostatic properties of Fe-based amorphous wires with diameter about 100μm. The samples were annealed at different conditions. The as-quenched sample had a weak increase (about 5%) of the magnetization with magnetic field decrease – the negative differential magnetic permeability could be observed in its hysteresis loops. The coercive force was about 0.2Oe. The conventional annealing decreased the value of the saturation field down to 5Oe without change of the coercive force value. When the annealing was accompanied with torsion stress the coercive force became less than 50mOe. After the current annealing any peculiarities disappeared in magnetization in a weak magnetic field.

The effect of magnetoelastic interaction on the GMI behaviour of Fe-, Co- and Co–Fe-based amorphous wires

The giant magnetoimpedance is the sensitive change in ac impedance value with the application of dc magnetic field when ac current passes through the sample. In the present work GMI properties of positive (Fe 77.5Si 7.5B 15), negative (Co 72.5Si 12.5B 15) and nearly zero ((Co 94Fe 6) 72.5Si 12.5B 15) magnetostrictive amorphous wires have been studied. The result indicates that the magnetostriction constant plays an important role in GMI property. The maximum GMI ratio (330%) and maximum field sensitivity (7% per A/m) are observed in (Co 94Fe 6) 72.5Si 12.5B 15 amorphous wire. The frequency response of the GMI characteristics of the above alloys has been measured and zero magnetostrictive (Co 94Fe 6) 72.5Si 12.5B 15 material showed better frequency response.

Origin of asymmetrical magnetoimpedance in a Co-based amorphous microwire due to dc bias current

Permeability spectra and asymmetrical giant magnetoimpedance (AGMI) have been studied in a Co-based amorphous microwire upon the application of a dc biasing current together with a shift of axial hysteresis loops. The permeability from wall motion of core domains is nearly constant, but the permeability from rotational magnetization of shell domains increases with the bias current. AGMI and its field sensitivity are realized for the bias current due to the influence of a unidirectional bias field on wall motion in the circumferential direction. In addition, helical internal anisotropy in this microwire also plays a significant role in responding differently to the axial magnetization process and thus to AGMI. The helical residual stress is estimated to be smaller in Co-based amorphous wire than that in Fe-based amorphous wire.

Correlation among impedance, longitudinal and circumferential permeability in Fe-based amorphous wires

A correlation is made among the impedance, the longitudinal permeability and the so called circumferential permeability in Fe-rich amorphous wires. The measurements of longitudinal permeability are made while an AC driving current is flowing through the wire for measuring the impedance components L and R . For particular combinations of the amplitude of the AC driving current, its frequency and the axial test field frequency, the longitudinal relative permeability achieves very high values (40–50×10 3) in comparison with those (1–2×10 3) measured in absence of the AC driving current. The circumferential permeability, deduced from the values of L and R, increases too but the increases are moderate in comparison with those of the longitudinal permeability and are favoured by torsional stresses. The results, discussed on the basis of the domain core-shell model, are ascribed to a coupling between the magnetization variations occurring in the outer shell of the wire and those occurring in the inner core due to the concomitant effect of the AC circular field and the AC axial field.

An analysis of interacting bistable magnetic microwires: from ordered to chaotic behaviours

Fe-based magnetostrictive amorphous wires are bistable exhibiting square-shaped longitudinal hysteresis loops. This is a consequence of their particular domain structure that allows them to be approached as magnetic dipoles. Arrays of such bistables wires are accordingly shown to be coupled by magnetostatic interactions. Furthermore, an analysis of these interactions allows us to conclude that depending on the relative strength of the magnetostatic and Zeeman interactions, ordered, complex or chaotic behaviours are found in the temporal variation of the array magnetisation.

A review on magneto-impedance effect in amorphous magnetic materials

Recently the magneto-impedance (MI) effect in soft magnetic amorphous wires and ribbons has attracted wide interest both for its application as sensitive magnetic field and current sensors and for studying from a physical point of view. This phenomenon is mainly observed in a series of Co and Fe-based amorphous magnetic wires and ribbons and change in MI as high as 360% have been observed. After suitable heat treatment, sensitivity can be further improved. This behaviour is related to the magnetic domain structure and magnetisation dynamics of the materials. The MI effect has potential applications in super sensitive sensors, high speed computer peripherals, micromagnetics, information apparatus, mechatronics, automobile, industrial robots, power electronics, medical electronics and industrial process control. In this paper we have reviewed the current state of research on this phenomena, particularly, the alloy preparation, measurement system and various annealing techniques used in the MI effect enhancement.

Effect of different heat treatments on magnetoelastic properties of Fe-based amorphous wire

The field dependence of Young’s modulus of Fe 77.5Si 7.5B 15 amorphous ferromagnetic wires were studied in as-quenched state and after furnace, current and pulse annealing. In as-quenched state, the change in Young’s modulus as a function of field is small due to induced large anisotropy during the quenching process. Annealing for short times is sufficient to remove most of the quenched stresses resulting in magnetic softening and large change in Young’s modulus. Further furnace or current annealing leads to surface crystallization which develops an easy axis in the circumferential direction, but such an easy axis was not observed in pulse annealed samples. The temperature of current annealed samples were calculated from resistance–temperature curve and the temperature of pulse annealed samples were estimated from T– t curve, where T is the annealing temperature and t the annealing time to reach the minimum value of coercivity.

Evaluation of helical magnetoelastic anisotropy in Fe-based amorphous wire from the decomposed susceptibility spectra

A novel method is introduced here to evaluate the intrinsic magnetic anisotropy from susceptibility spectra. The combination of two techniques namely, the decomposition of susceptibility spectra together with its dependence on applied torsion is employed to determine quantitatively the intrinsic helical anisotropy in an amorphous wire. The susceptibility spectra of Fe 77.5Si 7.5B 15 amorphous wires have been experimentally measured as a function of torsion. The reversible susceptibility is ascribed to wall motion of axial domains within the core, and to magnetization rotation within radial domains in the shell. The relaxation frequencies of these magnetization processes are evaluated to be 0.36 and 1.82 MHz, respectively. The static rotational susceptibility shows an asymmetric behavior with regards to positive and negative torsion angles, and is maximum at the torsion angle of 30°, which counterbalances the internal stress. Present results indicate the existence of an intrinsic helical anisotropy corresponding to an average helical stress of 33 MPa.

Peculiar behavior of the magneto-impedance in Fe-based amorphous wires under torsion

The inductive ( ωL) and resistive ( R) components of the impedance of an amorphous wire (Fe 77.5Si 7.5B 15) subjected to torsional stresses are measured. For a critical value of the AC driving current L abruptly increases due to irreversible magnetization processes in the circumferential configuration. Suitable combinations of the AC driving current amplitude and frequency give rise to a peak in the resistive variations and a minimum in the inductance. The inductance shows a bistable asymmetric hysteresis loop ( L vs. H). The torsional stress increases the coercivity of the longitudinal hysteresis loop of the wire but favors the reaching of the saturation magnetization at lower fields.

Decomposition of susceptibility spectra in a torsion-stressed Fe-based amorphous wire

The complex susceptibility spectra are measured as functions of the alternating-current field amplitude and the torsion angle in an Fe77.5Si7.5B15 amorphous wire. The susceptibility spectra show dispersion with a relaxation frequency of 40 kHz due to irreversible motion of the inner core domain walls when the driving field is larger than the threshold field of 10 mOe. The spectra for a small driving field can be decomposed into two relaxation dispersions by using the nonlinear curve fitting, one originating from reversible wall motion of the inner core domains and with a relaxation frequency of 0.36 MHz, and the other originating from reversible magnetization rotation in the outer shell domains and with relaxation frequency of 1.82 MHz. The static susceptibilities resulting from the reversible and the irreversible magnetization processes show an asymmetric change with positive and negative torsion angles.

ANALYSIS OF EDDY-CURRENT-LOSS IN Fe-BASED AMORPHOUS WIRES

On the basis of core-shell structure model of amorphous wires, for Fe-based amorphous wire we consider that there are an axial anisotropy Kc in the core and a radial anisotropy Ks in the shell, both of Kc and Ks are functions of λs and σ0,the constants of stress energy density. We deduce the ac circular permeability μφ(r) and calculate the anomaly factor of low-frequency eddy-current-loss for this model,η=2.2, from Maxwell equation and Ohm's law. Comparison of the theoretical value with the experimental results indicates that the magnetic structure of Fe-based amorphous wires can be well described by this improved core-shell structure model.

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.