A. Zhukov

Temperature dependence of the switching field and its distribution function in Fe-based bistable microwires

The switching field distribution for magnetization reversal in a single Barkhausen jump of a bistable Fe-based amorphous microwire as well as its temperature dependence have been investigated in the temperature range from 77 to 450 K. Two processes have been identified to be responsible for the temperature dependence of the switching field: magnetostrictive volume domain wall pinning on stresses and relaxation effects due to local structural rearrangements. While at low temperatures, pinning on the atomic level defects plays the dominant role, magnetostrictive pinning becomes more important at intermediate temperatures. A simple model is proposed considering both energy contributions that fits reasonably well with experimental data and allows us to interpret additionally the observed temperature dependence of the switching field fluctuations.

Stress induced magnetic anisotropy and giant magnetoimpedance in Fe-rich glass-coated magnetic microwires

The effect of conventional (CA) and stress annealing (SA) on magnetic properties of Fe74B13Si11C2 glass-coated microwires has been studied. CA treatment does not significantly change the character of the hysteresis loop. Under certain annealing conditions (annealing temperature, Tann>300 °C, applied stress, σ>700 MPa) rectangular hysteresis loop transforms into the inclined with magnetic anisotropy field above 1000 A/m. Such phenomenology has been related to the induction of transverse magnetic anisotropy by SA treatment. Under tensile stress the SA annealed microwire recovers rectangular hysteresis loop. Samples subjected to stress annealing show noticeable magnetoimpedance and stress impedance effects in spite of their large magnetostriction.

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.

Vortex-type domain structure in Co-rich amorphous wires

Investigation of the surface magnetic domain structure has been performed in Co-rich, nearly zero magnetostrictive, amorphous wires using magneto-optical Kerr effect magnetometry and microscopy. The formation and motion of a multidomain vortex-type structure with curved domain walls have been observed in amorphous wires. The possible origins of the existence of the vortex-type structures in these amorphous wires are discussed.

Effect of stress applied on the magnetization profile of Fe–Si–B amorphous wire

The effect of tensile stress, σ, on hysteresis loops and magnetization profiles of Fe77.5B15Si7.5 amorphous wires has been measured. Measurements performed by a short movable coil permit one to obtain the dependence of remanent magnetization, μ0Mr, on the position of this coil, L. Increasing applied stress in tensile stress is applied, the initially rectangular local hysteresis loop measured for L=4 cm (at l=8 cm) becomes inclined, but then recovers its rectangular shape for larger stress. The μ0Mr(σ) dependence shows an increase with σ for all L. The stress dependence of both μ0Mr and H* can be understood in terms of a competition between magnetostatic and magnetoelastic energy.

Circular magnetic bistability in Co-rich amorphous microwires

Circular magnetic bistability associated with a large Barkhausen jump between two states with opposite directions of circular magnetization have been observed by magneto-optical Kerr effect in nearly-zero magnetostrictive glass covered Co-rich amorphous microwire. The influence of external axial tensile stress on the circular switching field has been studied. Observed results have been related with a circular magneto-elastic anisotropy induced by a tensile stress in the outer transversally magnetized shell of the microwire.

Asymmetrical magneto-impedance effect in Fe-rich amorphous wires

Magnetoimpedance and magnetic properties of Fe-rich ferromagnetic amorphous wires of 0.050 mm diameter, prepared by an in-rotating-water technique following by a cold-drawing process to reduce the initial diameter of 0.125 mm, have been studied. A high value of magnetoimpedance phenomenon (about 60% real component and about 300% imaginary component) was measured in these microwires submitted to stress annealing by using the current annealing technique (annealing parameters: 150 mA during 90 min and 200 MPa). The application of a dc bias current affects strongly the field dependence of the magnetoimpedance ratio, inducing asymmetrical shape to the magnetoimpedance ratio. Such asymmetrical character is associated with the intrinsic helical anisotropy. The dc circular magnetic field produced by the dc electric current can modify in different ways the surface domain structure.Magnetoimpedance and magnetic properties of Fe-rich ferromagnetic amorphous wires of 0.050 mm diameter, prepared by an in-rotating-water technique following by a cold-drawing process to reduce the initial diameter of 0.125 mm, have been studied. A high value of magnetoimpedance phenomenon (about 60% real component and about 300% imaginary component) was measured in these microwires submitted to stress annealing by using the current annealing technique (annealing parameters: 150 mA during 90 min and 200 MPa). The application of a dc bias current affects strongly the field dependence of the magnetoimpedance ratio, inducing asymmetrical shape to the magnetoimpedance ratio. Such asymmetrical character is associated with the intrinsic helical anisotropy. The dc circular magnetic field produced by the dc electric current can modify in different ways the surface domain structure.

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 (ls) were obtained by using the small angle magnetization rotation method. The ls data obtained in these magnetic materials are consistent with those previously reported in amorphous ribbons and wires with similar composition. r 2002 Elsevier Science B.V. All rights reserved.

Amorphous and Nanocrystalline Soft Magnetic Materials: Tailoring of Magnetic Properties, Magnetoelastic and Transport Properties

It Is now nearly 30 years since the first metallic glass was produced by rapid quenching from the liquid state by Miroshnitchenko and Salli (Miroshnichenko and Salli, 1959) and Duwez et al. (Duwez et al., 1966; Klement et al., 1970). This proved to be a crucial point in opening up new fields of research in material science, magnetism and technology, such as metastable crystalline phases and structures, extended solid solubilities of solutes with associated improvements of mechanical and physical properties, nanocrystalline, nanocomposite and amorphous materials which, in some cases, have unique combinations of properties (magnetic, mechanical, corrosion, etc.). Technological development of the fabrication technique and studies of the structure, glass formation ability and thermodynamics and magnetism of amorphous alloys were intensively performed in 1960s–1970s. Main attention was paid to amorphous ribbons. These aspects have been extensively analyzed in few review papers and books (Duwez, 1966; Jones, 1973; Luborsky, 1983).

Tailoring of magnetic anisotropy in Fe-rich glass-coated magnetic microwires by thermo-mechanical annealing

The effect of thermal treatments such as conventional furnace annealing (CA) and annealing under tensile stress (SA) on the hysteretic magnetic properties of Fe74B13Si11C2 glass-coated microwires has been studied. CA treatment does not change the character of the hysteresis loop but coercivity, Hc, slightly decreases due to the internal stress relaxation. Under certain SA conditions (annealing temperature, Tann > 300 ◦ C, applied stress, σ> 700 MPa) the hysteresis loop becomes inclined with transverse anisotropy field about 1500 A/m. This modification of the hysteresis loop has been interpreted in terms of the change of the easy magnetization direction from axial to a transverse direction. On the other hand, samples subjected to stress annealing show noticeable (12%) magneto-impedance effect in spite of their large magnetostriction. Finally, application of tensile stresses to the stress-annealed sample results in the recovering of the rectangular hysteresis loop typical for the as-prepared state. This processing allows the tailoring of magnetic anisotropy in these microwires which is of interest for technological purposes.