Glass-covered Amorphous Microwires Research Articles

Investigation of helical magnetic structure in Co-rich amorphous microwires

The magnetization reversal process in Co-rich glass-covered amorphous microwires has been studied in presence of the torsion stress. The experiments have been performed using the transverse magneto-optical Kerr effect in crossed axial and circular magnetic fields. The influence of the torsion stress on the surface domain structure has been investigated. The angle of the surface helical structure has been determined based on the analysis of the stress-induced transformation of the Kerr hysteresis loops. The dependence of the angle of the helical structure on the value of the torsion stress has been obtained.

Domain wall dynamics in CoFeSiB microwires under axial applied stress

In this work, we present a domain wall dynamics study on Joule heated Co 68.15Fe 4.35Si 12.5B 15 glass-covered amorphous microwires. Three samples were annealed with: (i) DC current or AC current with frequency of (ii) 100 Hz and (iii) 500 Hz. The current density was equivalent to an annealing temperature of 250 °C. The permeability spectra were obtained from the magnetoimpedance measurements at different axial applied stresses. Contributions from domain wall motion and magnetization rotation to the total permeability were separated and analyzed. Without axial stress, the samples present a longitudinal anisotropy, which is converted to a core–shell domain structure (bamboo-like structure) when stress is applied. A huge increase of domain wall component of the permeability until a critical stress followed by a linear reduction is present in all samples. The main difference is that the domain wall contribution to the permeability and the critical stress are lowest for the DC annealed sample and reach a maximum for the sample annealed at 500 Hz. The results are discussed in terms of the field-induced anisotropy during the annealing and the internal stress distribution.

GMI Effect in Amorphous Glass Covered Microwires as a Function of the Internal Induced Stresses

The influence of the microwires diameter on the GMI effect, which consists of a significant change in the impedance of a piece of soft magnetic material driven by a high-frequency current when it is introduced into a static magnetic field, in CoFeSiB nearly zero magnetostrictive glass covered wires is presented. The largest GMI effect is obtained for microwires having the metallic core diameter of about 20 mum. The experimental results are discussed considering the calculated magnetic anisotropies induced by mechanical stresses. The GMI dependence on the longitudinal magnetic field is changing both the shape, from a double peak-like to a single-peak like curve, and the magnitude. The suitable combination metallic core diameter-glass cover thickness results, over the control of the internal stresses distribution, into an optimum GMI response

Internal stress distribution in DC joule-heated amorphous glass-covered microwires

As known, the magnetic properties of AGCMs are determined by the radial, azimuthal andaxial internal stresses induced during both the preparation process and the suitablethermal treatments of these microwires. In this paper we have proposed a theoretical modelin order to determine the total internal stresses induced during the dc joule-heatingthermal treatment (heating–crystallization–cooling). In this view (i) we have started fromthe internal stress values obtained in the preparation process, (ii) we have considered thesupplementary axial tensile stresses due to the mechanical drawing of the microwire duringthe preparation process and (iii) we have taken into account the difference between thethermal expansion coefficients of metal and glass. We have found that (i) the maximumvalue of the axial stresses obtained after the thermal treatment is bigger thanthat obtained in the preparation process, the difference being about 450 MPa, (ii)the maximum values for the azimuthal and radial stresses decrease by and MPa respectively, (iii) the dimensions of the cylindrical inner core increase significantly(by ), which involves an increase of the degree of magnetic order in the AGCMs andconsequently leads to the appearance of a large Barkhausen effect (LBE) in low axiallyapplied magnetic fields and (iv) the reduced remanence increases from 0.90 to 0.95.

Study of surface magnetic properties in Co-rich amorphous microwires

Magneto-optical investigations carried out on a Co-rich glass-covered amorphous microwire is presented. The appearance of circular magnetic bistability and the influence of tensile stress and high-frequency electric current on the surface magnetization reversal have been studied. The change of the mechanism of the magnetization reversal induced by the high-frequency electric current is also discussed.

Study of CoFeSiB glass-covered amorphous microwires under applied stress

Magnetoimpedance-based ferromagnetic resonance (FMR) studies of annealed Co68.15Fe4.35Si12.5B15 glass-covered amorphous microwires under stress are reported. The applied stress modifies the anisotropy and the domain structure present in each sample, in such a way that it can be studied through magnetoimpedance measurements and FMR dispersion relations extracted from them. From the fitting of the FMR dispersion relations, the magnitude and the orientation of the transverse anisotropy field, as well as an insight on the micromagnetic structure of glass-covered microwires, were obtained. From these studies, it can be concluded that a longitudinal anisotropy dominates the microwire behavior under zero stress. By applying an increasing stress to the microwires, an inner core with a longitudinal anisotropy surrounded by an outer shell with a circumferential anisotropy develops and dominates its magnetic behavior.

Magneto-optical investigation of high-frequency electric current influence on surface magnetization reversal in Co-rich amorphous microwires

Investigations of the surface magnetization reversal in Co-rich glass-covered amorphous microwires have been performed in the presence of high-frequency electric current flowing along the microwires. The experiments have been carried out using the magneto-optical Kerr effect in axial and circular magnetic fields. Strong influence of the high-frequency current on the mechanism of magnetization reversal and coercive properties has been found. It has been discovered that the high-frequency current induces the appearance of circular magnetic bistability. The high-frequency-induced effects are associated with the influence of the high-frequency electric current on the nucleation of circular magnetic domains and on the motion of domain walls in the outer shell of the microwires.

On dc Joule-heating effects in amorphous glass-covered Fe77.5Si7.5B15 microwires

The thermal effects of Joule-heating treatment on Fe77.5Si7.5B15 amorphous glass-covered microwires (AGCMs) are examined and, taking into account the appropriate boundary conditions at the metal–glass interface, a general solution of the equation describing the evolution of the sample temperature in the course of electrical direct current (dc) Joule-heating is found.A theoretical and thermo-numerical model for the calculation of the distribution of temperature in an AGCM through which an electrical current (dc) passes has been developed. This was done for the amorphous state (for sample temperature values below that corresponding to the onset of the crystallization process) and also for the transition from the amorphous to the crystalline phase (for both isothermal and non-isothermal processes) using the Johnson–Mehl–Avrami model. In the non-isothermal crystallization process, three crystallization products (αFe(Si), Fe2B and Fe23B6) were found, corresponding to the three stages of this process.

Magnetic and magnetotransport properties of Fe-based glass-covered microwires

Magnetic and magnetotransport properties of glass-covered amorphous microwires of nominal composition Fe89B1Si3C3Mn4 have been studied. Samples of two families with the same composition but different metallic core diameters were annealed in a furnace or by Joule heating. The electrical resistance was measured as a function of time during annealing to study the effects on the samples' microstructures (evolution from the amorphous to the crystalline phase). Static hysteresis loops were measured on all samples by means of a vibrating sample magnetometer. Giant magneto-impedance measurements (GMI) performed on a coaxial line using a vectorial network analyser at frequencies up to 6 GHz showed that furnace-annealed samples display larger anisotropies with respect to Joule-heated ones; however, Joule heating is more effective in improving the magneto-impedance response of the alloy. The maximum GMI ratio is ≈ 175% at 4 GHz. The influence of the different metallic core/total wire diameter on the induced anisotropies has been studied for the two families of samples through hysteresis loops and high-frequency GMI.

High-frequency magnetotransport properties in Co83.2Mn7.6Si5.9B3.3 glass-covered amorphous microwires

Abstract High-frequency ( 30 kHz –6 GHz ) giant magneto-impedance (GMI) in glass-covered Co 83.2 Mn 7.6 Si 5.9 B 3.3 amorphous wires has been studied as a function of annealing treatment. Normalization effects on GMI ratio have been studied by applying two different values of the maximum field.

FMR and domain structure in joule-heated glass-covered microwires

Abstract The magnetic domain structure of the Co 70.4 Fe 4.6 Si 10 B 15 glass-covered amorphous microwires Joule-heated of different annealing currents (temperatures) is studied. From the magnetization curves and ferromagnetic resonance features obtained from the impedance spectra measured at different magnetic fields, a domain structure is proposed for the as-produced and Joule-heated microwires.

Surface magnetization reversal in Co-rich amorphous microwires in perpendicular magnetic fields

Investigations of magnetization reversal in Co-rich amorphous glass-covered microwires were performed using the magneto–optical Kerr effect in perpendicular axial and circular magnetic fields. The magnetization reversal consists of the rotation of the magnetization and nucleation of the circular domain in the outer shell of the microwire. The model, which takes into account the influence of DC electric current on the nucleation process, has been applied.

Domain structure in Joule-heated CoFeSiB glass-covered amorphous microwires probed by magnetoimpedance and ferromagnetic resonance

Impedance spectra (100 kHz⩽f⩽1.8 GHz) were measured at different magnetic fields, and magnetoimpedance and magnetization measurements were performed in as-produced and Joule-heated Co70.4Fe4.6Si10B15 glass-covered amorphous microwires. From the magnetization curves and ferromagnetic resonance features obtained from the impedance spectra, it was possible to propose a domain structure in the as-produced microwires, as well as to follow its evolution with the annealing current. The inner core and outer shell domain structure were observed. The outer shell domains evolve from a circumferential, in the as-cast sample, to a helical structure in the case of the annealed samples. On the other hand, the inner core evolves from a domain structure typical of a radial anisotropy to a longitudinal one. This domain structure evolution is explained in terms of the combined effects of the stress, promoted by the annealing temperature, and the magnetic field caused by the annealing current.

Effect of thermal treatments on the magnetic inhomogeneities distribution in magnetic amorphous wires and microwires

Positive magnetostrictive Fe/sub 77.5/Si/sub 7.5/B/sub 15/ conventional amorphous wires (CAW) 125 /spl mu/m in diameter and amorphous glass-covered microwires (AGCW) with a metallic core diameter of 35 /spl mu/m have been annealed below and above their crystallization temperature, which produces precipitation of the /spl alpha/-Fe(Si) phase within the amorphous matrix. The J-H loop and the temperature dependence of the magnetization and the coercive field reveal the presence of two different magnetic phases in the thermally treated samples. The effect of the thermal treatment on the magnetic domain structure in both CAW and AGCW and its influence on their soft magnetic properties are discussed.

Separation of circumferential magnetic components from MI spectra in laser-annealed Co-based amorphous microwires

A commercial glass-covered Co-based amorphous microwire (Co/sub 66/Fe/sub 3.8/Ni/sub 1.4/B/sub 11.5/Si/sub 14.6/Mo/sub 1.7/) with metallic core diameter of 17 /spl mu/m was annealed in air by illuminating the pulsed Nd:YAG laser beams under longitudinal and transverse annealing fields, denoted by H/sub l/ and H/sub t/, respectively. The static susceptibilities by domain-wall motion and magnetization rotation, /spl mu//sub dw/ and /spl mu//sub rot/, were separated from the circumferential complex permeability extracted from impedance spectra. The /spl mu//sub rot/ shows a maximum value of the laser-annealed sample with H/sub l/=20 Oe, which indicates the increased volume of axial domain in the core by laser-annealing under longitudinal magnetic field. The /spl mu//sub dw/ shows maximum value at laser-annealed sample with H/sub t/=20, indicating that the volume of axial domain in core is increased by laser annealing under transverse magnetic field.

Giant magnetoimpedance in Co-based microwire annealed by pulsed Nd:YAG laser

The influence of laser annealing on giant magnetoimpedance (GMI) effect of glass-covered Co-based amorphous microwires was investigated by illuminating pulsed Nd:YAG laser beam on the etched microwires. The maximum GMI ratio at 5 MHz under cyclic magnetic field frequency increases from 60% for the as-etched microwire up to 73% and 110% after laser annealing without and with the annealing magnetic field, respectively.

Interaction between Co-rich glass-covered microwires

Investigations on the magnetic reversal in a system of two glass-covered Co-rich amorphous microwires with circular bistability have been performed using the magneto-optical Kerr effect technique. The experimental configuration, when the electric current producing the circular magnetic field flows through the wires in opposite directions, has been employed first for the glass-covered microwires. The peculiarities of the obtained hysteresis loops reflect the influence of the axial stray fields produced by the inner cores of the microwires on the circular magnetization reversal in the outer shells of the neighbouring microwires of the system. The experimental results have been analysed considering the mutual influence of microwires in the condition of the circular bistability effect.

Circular magnetic bistability induced by tensile stress in glass-covered amorphous microwires

Investigations of magnetic reversal in Co-rich glass covered amorphous microwires were performed using the magneto-optical Kerr-effect technique. The appearance of circular magnetic bistability was found in the presence of external tensile stress. A tensile-induced large Barkhausen jump of circular magnetization is associated with a change of the value of the magnetostriction constant induced by stress and by rearrangement of domain structure in the outer shell of the microwire.

Magnetostriction of glass-coated Co-rich amorphous microwires and its dependence on current annealing

We present results on the saturation magnetostriction constant of four glass-covered Co-rich amorphous microwires for as-prepared and current annealed samples. The values of the saturation magnetostriction constant ( λ s) were obtained by using the small angle magnetization rotation method. The λ s data obtained in these magnetic materials are consistent with those previously reported in amorphous ribbons and wires with similar composition.

Giant magnetoimpedance in glass-covered amorphous microwires at microwave frequencies

In this work, results on the giant magnetoimpedance of glass-covered amorphous microwires with nominal composition Co70.4Fe4.6Si15B10 are presented. The impedance Z=R+iX has been investigated as function of frequency (1 MHz–1.8 GHz) and magnetic field (up to ±400 Oe), using a HP4396B impedance analyzer and an appropriate coaxial microwave cavity. The effects of the thermal treatments (Joule heating, from 1 up to 50 mA for 10 min) for anisotropy induction and/or to induce recrystallization have been investigated.