Amorphous Microwires Research Articles

Surface magnetic structures in amorphous ferromagnetic microwires

The spatial period of magnetization perturbations that occur near the surface of magnetic nanotube or nanowire under the influence of surface magnetic anisotropy is determined by means of numerical simulation as a function of the sample geometry and material parameters. The surface magnetization distribution obtained is then used to estimate the period of the surface magnetic texture in amorphous microwire of several micrometers in diameter by means of appropriate variational procedure. The period of the surface magnetic texture in amorphous microwire is found to be significantly smaller than the wire diameter.

Torsion Stress Induced Magnetic Switching in Amorphous Microwires

The mechanisms of magnetization reversal related to anisotropy change were analyzed using magneto-optical Kerr effect in Co- and Fe-rich microwires with different signs of magnetostriction. The reversible switching between inclined magnetic states and transformation of different inclined states was controlled by external torsion stress.

Electromagnetic properties of polymer composites Co52Cr22Ni10W7,5Fe1,5 i Fe59Cr21,5Ni7Si1Mn10 at Ku band

The electromagnetic properties of polymer composites can be obtained by inverting the numerically simulated reflection S11 and transmission S21. Two composites containing amorphous glass-coated microwire Co52Cr22Ni10W7,5Fe1,5 and Fe59Cr21,5Ni7Si1Mn10 are investigated in Ku band. The results show that the imaginary part of permittivity is quite weak, and can be considered as zero, which means that there is no dielectric loss. It is shown that the decrease in the spacing between the inclusions strongly affects the magnetic response in comparison with the dielectric response of the two composites, which is characterized by a ferromagnetic resonance peak FMR. We also present an investigation related to an electromagnetic radiation absorber for a preselected frequency range between 12 and 18 GHz. With the increase of microwire spacing, the minimum reflection loss decreases firstly and then increases, and shifts towards lower frequency band.

Surface and volume waves in ferrodielectric–magnetically active material structures

The propagation of surface waves along the interface between a ferrodielectric and a material that represents an array of amorphous ferromagnetic microwires has been studied. The dispersion characteristic of a magnetically controlled TE wave has been obtained, and frequency intervals have been found in which surface or localized, partially localized, and volume waves may exist. It has been shown that a TM wave in the given structure cannot be a surface wave.

Synthesis and Characterization of Highly Elastic TiCu-Based Amorphous Micro-Wires

A series of TiCu-based quaternary amorphous wires from a deep eutectic alloy composition were prepared by arc-melting and melt-extraction methods. Continuous amorphous wires with good white luster and smooth surface were obtained in Ti25Zr15 Cu60-xNix (x = 0, 5, 10, 15 mol%) alloys. The TiCu-based amorphous wires exhibit high tensile strength exceeding 1.3 GPa and high elastic limit of over 1.4%. Good combine of mechanical properties make them viable for use in many micro mechanical systems.

Structural and magnetic transformations in amorphous ferromagnetic microwires during thermomagnetic treatment under conditions of directional crystallization

As produced glass-coated ferromagnetic microwires typically have an amorphous state and demonstrate ultra-soft magnetic properties. For many applications, microwires with strong hard magnetic properties are of interest. A giant increase in coercivity has been recently reported for microwires subjected to directed crystallization. This paper confirms the coercivity increase up to 42 kA/m for wires of composition Fe4.3Co67.7Si11B14Cr3 after magnetic-field assistant directed crystallization. To understand the effect of the directional crystallization on wire magnetic properties and to develop the reliable annealing technology the structural and mechanical transformation occurring during various stages of the annealing processes were investigated.

Mechanical properties and internal quenching stresses in Co-rich amorphous ferromagnetic microwires

Abstract The whole set of geometrical, mechanical and magnetic parameters of Co-rich amorphous ferromagnetic microwires very promising for the development of sensitive stress and Giant Magneto-Impedance sensors have been determined by means of scanning electron microscopy, selective nanoindentation and small angle magnetization rotation method. The magnetostriction constants obtained are sensitive to the true microwire compositions. The experimentally estimated amplitudes of the residual quenching stress are mainly determined by the ratio of the inner and outer wire diameters. They are found to be in good correspondence with the theoretical values calculated based on the theory of viscoelasticity.

Engineering of giant magnetoimpedance effect of amorphous and nanocrystalline microwires

We present our studies of the factors affecting soft magnetic properties and giant magnetoimpedance effect in thin amorphous and nanocrystalline microwires. We showed that the magnetoelastic anisotropy is one of the most important parameters that determine magnetic softness and GMI effect of glass-coated microwires and annealing can be very effective for manipulation the magnetic properties of amorphous ferromagnetic glass-coated microwires. Considerable magnetic softening and increasing of the GMI effect is observed in Fe-rich nanocrystalline FINEMET-type glass-coated microwires after the nanocrystallization.

Ferromagnetic glass-coated microwires with good heating properties for magnetic hyperthermia.

The heating properties of Fe71.7Si11B13.4Nb3Ni0.9 amorphous glass-coated microwires are explored for prospective applications in magnetic hyperthermia. We show that a single 5 mm long wire is able to produce a sufficient amount of heat, with the specific loss power (SLP) reaching a value as high as 521 W/g for an AC field of 700 Oe and a frequency of 310 kHz. The large SLP is attributed to the rectangular hysteresis loop resulting from a peculiar domain structure of the microwire. For an array of parallel microwires, we have observed an SLP improvement by one order of magnitude; 950 W/g for an AC field of 700 Oe. The magnetostatic interaction strength essential in the array of wires can be manipulated by varying the distance between the wires, showing a decreasing trend in SLP with increasing wire separation. The largest SLP is obtained when the wires are aligned along the direction of the AC field. The origin of the large SLP and relevant heating mechanisms are discussed.

Tensile Strength Reliability Analysis of Cu48Zr48Al4 Amorphous Microwires

Uniform Cu48Zr48Al4 amorphous microwires with a high surface quality are fabricated by a melt extraction technique. The mechanical property of microwires is evaluated via tensile tests. To estimate the strength scattering, statistical analysis of fracture strengths is conducted using logarithmic normal distribution, and two- and three-parameter Weibull analysis, severally. The results show that the tensile strengths of Cu48Zr48Al4 amorphous microwires range from 1724 to 1937 MPa with the arithmetical average value of 1836 MPa, and the arithmetical standard deviation of 56.4 MPa. The geometric mean of fracture strength is 1840 MPa using logarithmic normal distribution statistical analysis. Using two- and three-parameter Weibull analysis, the Weibull modulus and fracture threshold value are respectively calculated for 34.8 and 1483 MPa, which shows the excellent tensile mechanical properties with a high predictability of Cu48Zr48Al4 amorphous microwires and further indicates the great potential of application.

Frequency and Magnetic Field Dependence of the Skin Depth in Co-rich Soft Magnetic Microwires

We studied giant magnetoimpedance (GMI) effect in magnetically soft amorphous Co-rich microwires in the extended frequency range. From obtained experimentally dependences of GMI ratio on magnetic field and different frequencies we estimated the penetration depth and its dependence on applied magnetic field and frequency

Validation of the Fixation of Amorphous Magnetic Glass-coated Magnetic for Biomedical Applications

Sufficient control of the mechanical stress and temperature at the tissue-implant interface after the process of implantation is an important part of validation of the implantation and acceptance of the implant by the internal environment of the body. For this purpose being able to measure these values without contact and with the smallest possible interference in the implant is important. For these measurements the use of amorphous magnetic glass-coated microwires (AMGCM) is very promising.In comparisons with the sensors which are currently used in intelligent implantations, e.g. RFID sensors, which have dimensions on the order of tens of cm and are relatively expensive, AMGCM have a great advantage in sizes (less than 50 μm in diameter and for a functional sensor a length of 5 mm is minimally necessary) and their manufacture is very inexpensive.This work is focused on the control of fixation of an AMGCM in a sample of the manufacturing technology Direct Metal Laser Sintering. In addition to the metal magnetic core itself, the fixation of an AMGCM has, due to the magneto-elastic effect, an important influence on the magnetic characteristics of the microwire used. The volume of the fixation material and thus also the working force on the microwire influences the sensitivity of the microwire and influences its Curie temperature (TC), which is an important variable in preparation of the composition of the metal core of the microwire.

Current controlled switching of impedance in magnetic conductor with tilted anisotropy easy axis and its applications.

We present a concept and prototype of a memory element based on current driven magneto-impedance (MI) effect that stores the binary data (0, 1) as the orientation of the magnetization. The magnetization orientation in the surface layer with tilted anisotropy easy axis can be switched controllably between two stable states by applying current pulses of the appropriate sign, and can be detected by sensing the impedance. We demonstrated the functioning of a non-volatile magnetic memory with a read speed performance up to and above 2 GHz. A prototype of a memory element was realized on a short piece of amorphous microwire, as this material exhibits the highest MI effect, and the required anisotropy can be quite easily obtained. Nevertheless, this concept can be extended to other materials and geometries exhibiting MI effect and possessing a required magnetic anisotropy.

Improving mechanical and magnetocaloric responses of amorphous melt-extracted Gd-based microwires via nanocrystallization

We report on the structural, mechanical, and magnetocaloric properties of annealed melt-extracted Gd53Al24Co20Zr3 amorphous microwires of ∼70 μm diameter. During heat treatment small islands of nanocrystallities are generated and isolated in the amorphous region for the wires. The size of the nanocrystallities ranges from 5 nm to 10 nm. The observed lattice distortion from the nanocrystallities causes changes in the magnetic properties of the wires. The annealing temperature of 100 °C has the largest strength (1845 MPa) as compared to wires annealed at other temperatures. This is likely to trigger nanophase transformation in the amorphous region and these nanocrystals have been preserved through the increase of annealing temperature. The formulation of the nanocrystalline islands is also verified by the selected-area electron diffraction (SAED). The microwires exhibit a large and reversible magnetocaloric effect (MCE), with the maximum isothermal magnetic entropy change (−ΔSM) and refrigerant capacity (RC) values of 9.5 J/kg K and 689 J/kg respectively for the microwire annealed at 100 °C. This RC is about 35%, 67%, and 91% larger than those of bulk Gd53Al24Co20Zr3 (∼509 J/kg), Gd (∼410 J/kg), and Gd5Si2Ge1.9Fe0.1 (∼360 J/kg) regardless of their ordering temperatures. These results demonstrate the ability to tune the mechanical and magnetic properties of the microwires by thermal annealing.

The stress components effect on the Fe-based microwires magnetostatic and magnetostrictive properties

For glass-coated amorphous ferromagnetic Fe-based microwires both joint and separate effect of metallic nucleus diameter, d, and the ratio of metallic nucleus diameter to the total diameter of microwire in glass shell, d/D, on magnetic properties is investigated. Thereby the contribution of both shell-induced stresses, associated with the ratio of diameters, and internal nucleus stresses (residual, quenching), associated with the diameter of the nucleus are estimated. A strong and non-monotonic effect of the metallic nucleus diameter and metallic nucleus diameter/total microwire diameter ratio on magnetostatic and magnetostrictive properties was established. For analysis, we considered magnetically bi-stable microwires of “classic” Fe77.5Si7.5B15 alloy with positive magnetostriction coefficient.

Estimation of the frequency and magnetic field dependence of the skin depth in Co-rich magnetic microwires from GMI experiments

Abstract We studied giant magnetoimpedance (GMI) effect in magnetically soft amorphous Co-rich microwires in the extended frequency range. From obtained experimentally dependences of the GMI ratio on magnetic field at different frequencies we estimated the penetration depth and its dependence on applied magnetic field and frequency.

Engineering of Giant Magnetoimpedance Effect of Amorphous and Nanocrystalline Microwires

We present an overview of the factors affecting soft magnetic properties and giant magnetoimpedance (GMI) effect of thin amorphous wires. Low coercivity and high GMI effect have been observed in as-prepared Co-rich microwires. We showed that the magnetoelastic anisotropy is one of the most important parameters that determines the magnetic softness and GMI effect of glass-coated microwires, and annealing can be very effective for manipulation of the magnetic properties of amorphous ferromagnetic glass-coated microwires. After annealing of Co-rich microwires, we can observe the transformation of inclined hysteresis loops to rectangle and coexistence of fast magnetization switching and GMI effect in the same sample. We demonstrated that the switching field value of microwires can be tailored by annealing in the range from 4 to 200 A/m. On the other hand in Fe-rich FeCuNbSiB microwires after appropriate annealing, we observed considerable magnetic softening and GMI effect enhancement.

Features of Amorphous Microwires With Spontaneous and Induced Magnetic Bistability

We demonstrate that in Co-rich amorphous microwires with vanishing magnetostriction coefficient, a conventional annealing is quite an efficient method for tailoring of magnetic properties. We observed induced magnetic bistability allowing the observation of fast domain-wall (DW) propagation and giant magnetoimpedance effect simultaneously in the same sample. Moreover, DW dynamics in microwires with induced magnetic bistability presents unusual dependence on applied stress, exhibiting a subsequent growth of DW velocity. For interpretation of these observed changes of hysteresis loops by annealing, we consider stress dependence of the magnetostriction.

A high-sensitivity scanning magnetometer based on the giant magneto-impedance effect for measuring local magnetic fields of corrosion currents

The design, main characteristics, and specific features of a new high-sensitivity magnetometer based on the giant magneto-impedance (GMI) effect in amorphous ferromagnetic microwires are considered. It is shown that, in addition to measuring homogeneous fields, the device is capable of detecting weak local magnetic fields of conduction currents and ion currents involved in corrosion processes. Results of in situ magnetic measurements of corrosion processes in the model system of copper–zinc in a sulfuric acid solution qualitatively agree with the data of direct corrosion tests employing the standard gravimetric method.

Tailoring of Magnetic Properties and Magnetoimpedance Effect in Thin Amorphous Wires

We have studied the effect of annealing conditions on magnetic properties of amorphous CoFeNi-based glasscoated microwires. We show that annealing can be very effective for manipulation the magnetic properties of amorphous ferromagnetic glass-coated microwires. Low coercivity and high giant magnetoimpedance (GMI) effect have been observed in as-prepared Co-rich microwires. After annealing of Co-rich microwires we can observe transformation of inclined hysteresis loops into rectangular and coexistence of fast magnetization switching and GMI effect in the same sample. We demonstrate that the switching field value of microwires can be tailored by annealing in the range from 4 to 200 A/m.