Amorphous Ferromagnetic Microwires Research Articles

Tuning the giant magnetoimpedance response of a glass-coated microwire reinforced polymer by in-situ laser annealing

The ability to modify the giant magnetoimpedance (GMI) effect in amorphous glass-coated ferromagnetic Co-based microwire reinforced polymer via laser irradiation is presented. Through in-situ laser annealing of microwires embedded into a polymer matrix, a 25 % improvement in the GMI response is demonstrated after only 4.9 min of annealing. This improvement is compared to a conventional oven anneal technique, requiring an hour of oven annealing, subsequent sample cooling and polymer casting. This unique in-situ technique offers a novel and expedient path toward tailorable multi-functional composites in the areas of tunable electromagnetic shielding, structurally integrated antennas and magnetic sensors.

Measurements of Stray Magnetic Fields of Fe-Rich Amorphous Microwires Using a Scanning GMI Magnetometer

A scanning magnetometer based on a magnetoimpedance sensor with a 1 mm spatial resolution and 10 nT sensitivity was used to study stray magnetic fields of Fe74B13Si11C2 amorphous ferromagnetic microwires. Spatial magnetic images and vertical component profiles of stray magnetic fields of the studied microwires were obtained in a longitudinal homogeneous magnetic field of Helmholtz coils with a strength in the range of ±600 A/m. A magnetic calculation method is suggested that allows for using the measured magnetic fields to determine the magnitude and pattern of magnetization for the microwire. Characteristic values of the microwires’ average magnetization and width of closure domains for various values of bias fields were found.

High-Sensitivity Wireless Sensing Using Amorphous Magnetic Microwires

Glass-coated amorphous ferromagnetic microwires subjected to variations in mass loading and parallel wire arrays with 0.5–6-cm interwire spacing were found to deliver exceptional magnetomechanical and wireless giant magnetoimpedance (GMI) responses, in the kilohertz and microwave range, respectively. The microwires allow wireless quantification of microgram mass differences: the magnetomechanical resonance frequency measured in zero applied field demonstrates an approximately linear decrease of 3 Hz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{g}$ </tex-math></inline-formula> , and a sensitivity response that is ten times greater than that reported for commercial METGLAS-type amorphous magnetic ribbons of comparable length. Microwave giant magnetoimpedance data collected from planar arrays of parallel microwires show either constructive or destructive interference when compared to data obtained from a single microwire. The exceptional responsiveness of the glass-coated amorphous ferromagnetic microwires to mass loading and to geometric arrangement, along with their small diameter and ease of fabrication, highlights their promise for a wide variety of sensor applications, including biosensing, civil infrastructure monitoring, and high-throughput remote detection schemes.

Prospects for using amorphous ferromagnetic alloy microwire for reinforcement of cement mortar

Traditionally, fibers for fiber-reinforced concrete are made of metal, polypropylene, basalt or glass. На сегодняшний день для строительства актуально использование волокон с уникальными электрофизическими свойствами. The possibilities of using a microwire made of an amorphous ferromagnetic alloy based on cobalt with a shell of borosilicate glass in concrete technologies are studied in this paper. The influence of the content of fibers of different sizes (length 7 and 15 mm) on the rheological and physico-mechanical properties of the solution was established. The deterioration of the workability of mixtures and the average density of the composite with the introduction of the studied fiber is shown. It has been established that the spread diameter of the mortar mixture with a fiber content of 0.5...3.0 % by weight of Portland cement is reduced by 9.8...26.1% compared to the control composition. It is shown that the short fiber (7 mm) at the maximum content (3 %) leads to a more significant decrease in the average density (up to 9.6 %) compared to the long fiber (15 mm) of the same concentration (reduction is no more than 4 %). A positive effect on the flexural strength and crack resistance of the solution was established. The increment of flexural and compressive strength ranges from 1.11 to 1.54 and from 0.99 to 0.78 respectively with increasing fiber concentration. The presence of fiber in the composition of the solution allows you to increase the crack resistance from 0.098 to 0.164. The increase in the crack resistance coefficient for compositions with a fiber 7 mm long is 51...68 % and compositions with a fiber 15 mm long is 22...37 %. The possibility of using such microwire based on a ferromagnetic alloy for dispersed reinforcement of cement solutions opens up prospects for the creation of “smart” materials.

Method for evaluating the temperature of amorphous ferromagnetic microwires under Joule heating

The results of comparative studies of the electrically conductive properties of Co69Fe4Cr4Si12B11 glass coated amorphous microwires obtained during their heat treatment in a conventional furnace and by the Joule heating method are presented. The fully crystallized microwire dramatically changes its electrically conductive properties. We found that the crystallized microwire has a temperature coefficient of resistance, α = 315*10-6 1/ °C. The crystallized microwire was used as a reference resistance thermometer under Joule heating for determining the temperature of the microwire as a function of the applied thermal power T(P). This dependence obtained was used to determine the temperature dependence of the resistance RM(T) of other microwire samples in an amorphous or partially crystallized state of the same series. The proposed method allows to select thermal modes during Joule annealing of microwires and to compare the resistive, magnetic and structural-phase properties of microwires after thermal effects.

Influence of Joule heating on electrical resistivity in Co-rich amorphous microwires

The paper investigates the electrical resistivity of two types of the glass-coated Co-rich amorphous ferromagnetic microwires during the Joule heating by direct current. We measured the relationships between the microwire’s resistivity and the power, which applied to the samples in as-prepared and crystallized conditions. Both types of microwires were demonstrated to completely crystallize on exposure to a temperature of more than 600 °C. During heating by a power up to 2.5 W (~400 °C), the microwires with Mo-Ni content were characterized by a monotonic resistivity increase with the temperature. But the microwires with Cr content had a well-marked resistivity minimum near the temperature Tм ~ 163 °C. This minimum shifted to a temperature value of ~260 °C after annealing. The research shows that the temperature dependence of resistivity in the temperature range below Tм obeys the f(T) = -ln(T) law.

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The paper investigates the electrical resistivity of two types of the glass-coated Co-rich amorphous ferromagnetic microwires during the Joule heating by direct current. We measured the relationships between the microwire’s resistivity and the power, which applied to the samples in as-prepared and crystallized conditions. Both types of microwires were demonstrated to completely crystallize on exposure to a temperature of more than 600 °C. During heating by a power up to 2.5 W (~400 °C), the microwires with Mo-Ni content were characterized by a monotonic resistivity increase with the temperature. But the microwires with Cr content had a well-marked resistivity minimum near the temperature Tм ~ 163 °C. This minimum shifted to a temperature value of ~260 °C after annealing. The research shows that the temperature dependence of resistivity in the temperature range below Tм obeys the f(T) = -ln(T) law.

Boosting the Tunable Microwave Scattering Signature of Sensing Array Platforms Consisting of Amorphous Ferromagnetic Fe2.25Co72.75Si10B15 Microwires and Its Amplification by Intercalating Cu Microwires.

The following work addresses new configurations of sensing array platforms that are composed of Co-based amorphous ferromagnetic microwires (MWs) to obtain an enhanced modulation of the microwave scattering effects through the application of low strength DC or AC magnetic fields. An amorphous MW is an ultrasoft ferromagnetic material (coercivity ~0.2 Oe) with a circumferential magnetic anisotropy that provides a high surface sensitivity when it is subjected to an external magnetic field. Firstly, microwave scattering experiments are performed as a function of the length and number of MWs placed parallel to each other forming an array. Subsequently, three array configurations are designed, achieving high S21 scattering coefficients up to about −50 dB. The influence of DC and AC magnetic fields on S21 has been analyzed in frequency and time domains representation, respectively. In addition, the MWs sensing array has been overlapped by polymeric surfaces and the variations of their micrometric thicknesses also cause strong changes in the S21 amplitude with displacements in the frequency that are associated to the maximum scattering behavior. Finally, a new concept for amplifying microwave scattering is provided by intercalating Cu MWs into the linear Co-based arrays. The designed mixed system that is composed by Co-based and Cu MWs exhibits a higher S21 coefficient when compared to a single Co-based MW system because of higher electrical conductivity of Cu. However, the ability to modulate the resulting electromagnetic scattering is conferred by the giant magneto-impedance (GMI) effects coming from properties of the ultrasoft amorphous MWs. The mixed array platform covers a wide range of sensor applications, demonstrating the feasibility of tuning the S21 amplitude over a wide scattering range by applying AC or DC magnetic fields and tuning the resonant frequency position according to the polymeric slab thickness.

An Indirect Method of Micromagnetic Structure Estimation in Microwires.

The tunable magnetic properties of amorphous ferromagnetic glass-coated microwires make them suitable for a wide range of applications. Accurate knowledge of the micromagnetic structure is highly desirable since it affects almost all magnetic properties. To select an appropriate wire-sample for a specific application, a deeper understanding of the magnetization reversal process is required, because it determines the measurable response (such as induced voltage waveform and its spectrum). However, the experimental observation of micromagnetic structure of micro-scale amorphous objects has strict size limitations. In this work we proposed a novel experimental technique for evaluating the microstructural characteristics of glass-coated microwires. The cross-sectional permeability distribution in the sample was obtained from impedance measurements at different frequencies. This distribution enables estimation of the prevailing anisotropy in the local region of the wire cross-section. The results obtained were compared with the findings of magnetostatic measurements and remanent state analysis. The advantages and limitations of the methods were discussed.

Magnetoimpedance effect in amorphous Co-rich ferromagnetic microwires and its application as low-field sensor

The magnetoimpedance in amorphous microwires with a nominal composition of Co67Fe4Si14B15 has been investigated. The measurements were carried out with an Agilent 4395A network analyzer in the frequency range from 100 kHz to 60 MHz. The experimental setup for magnetoimpedance measurements and the analysis of the results are presented. Our results show that an optimum frequency exists, where the magnetoimpedance ratio is maximum for all studied frequencies. In this frequency, the amorphous microwire is very sensitive to variations of the dc magnetic field. Therefore, we propose a possible application as a low dc field sensor.

Correlation of electrical and magnetic properties of Co-rich amorphous ferromagnetic microwires after DC Joule heating treatment

The present work describes the investigation of electrical and magnetic properties of the glass-coated Co-rich amorphous ferromagnetic microwires, having typical metallic core diameters d = 13–20 μm and tailoring by the direct current Joule heating. During this treatment, a continuous monitoring of the microwire condition was carried out, measuring its resistance by means of a DC bridge circuit. The heating of the microwire sample was provided by a direct current in the range from 20 mA to 63 mA. In this heating currents range, the microwires show a slight change in their resistivity. After annealing the resistivity of microwires may increase of about 1% with respect to as-prepared one. Depends on the heating current, the hysteresis loops of annealed microwires demonstrated the transition from a quasi linear type to a bistable one and vice versa. The maximum of the giant magnetic impedance ratio was observed in such microwires, which had a hysteresis loops describable by a near-zero anisotropy field.

Scanning magnetic microscope based on magnetoimpedance sensor for measuring of local magnetic fields

A scanning magnetic microscope based on an off-diagonal magnetoimpedance sensor is presented. As a sensor, we use a 4 mm segment of glass covered microwire, having a metallic core diameter of 13.5 μm and CoFeCrSiB composition and a pick-up coil wound around the microwire containing 70 turns. The magneto-impedance sensor is fixed perpendicular to the surface of the sample, in such a way that the distance between the tip of the microwire and the sample is about 200 μm. The relative movement of the sample and the GMI sensor is carried out using a non-magnetic X-Y positioner. Measurements are taken inside the magnetic screen. For test measurements, samples in the form of the letters IWMW – of the conference abbreviation are used. The samples were made based on thin copper wire, Fe-rich amorphous ferromagnetic microwires and printed by laser-jet printer. Clear magnetic images were obtained on all samples, which demonstrates the high practical potential of the proposed method.

Study of bistable behaviour in interacting Fe-based microwires by first order reversal curves

Amorphous ferromagnetic Fe-based microwires (MWs) have a magnetic structure consisting mainly of a single longitudinal domain and small closure domains at both ends. A rectangular hysteresis loop is then observed according to the fast domain wall propagation along the microwire. This type of material is a good physical example of the idea of a magnetic relay hysteron as described in Preisach model of hysteresis. The hysteron was defined as a mathematical operator acting on the field and producing rectangular loops whose superposition gives out the hysteresis loop. The hysteron idealization is frequently used to describe and interpret FORC (First Order Reversal Curve) diagrams by comparison with Preisach plane. The central idea of this work is to study the FORCs of a real physical sample that behaves closely to the ideal hysteron, both isolated and interacting with a twofold aim. On one hand, providing a better understanding of FORC measurements, and, on the other, analyzing the magnetization reversal processes in microwires with rectangular hysteresis loops. While for a single microwire the behaviour is that expected for a hysteron, both in the hysteresis loop and in the FORC diagram, the magnetostatic interaction between two microwires breaks with the ideal behaviour due to the change in the domain wall mobility at the end of the wires.

Tunable domain wall dynamics in amorphous ferromagnetic microwires

Abstract In this work, we show the possibility of tuning the domain wall dynamics in amorphous ferromagnetic microwires by means of thermal annealing. We investigate the effect of annealing time and temperature on the field dependence of the domain wall velocity in magnetically bistable Fe- and CoFeNi-based microwires. We demonstrate that the magnitude of the magnetostriction coefficient determines the tendency of the domain wall mobility and velocity change and we relate the magnetostriction coefficient to the stress relaxation upon annealing. Thus, in the case of Fe-based microwires with large positive magnetostriction ∼10−6 the stress relaxation caused by the annealing leads to an increase of the velocity and mobility of the domain wall, while the same parameters of the domain wall dynamics for CoFeNi-based microwires with nearly zero magnetostriction coefficient ∼10−7-10−8 significantly decrease. Growth of the minimum magnetic field for domain wall propagation upon annealing is observed in CoFeNi microwires with vanishing magnetostriction coefficient. This influence of annealing on the domain wall dynamics of CoFeNi microwires is explained by considering domain wall stabilization due to pair ordering. The opposite tendency observed for Fe-based microwires with only one transition metal is associated with the stress relaxation upon annealing.

Structure of head-to-head domain wall in cylindrical amorphous ferromagnetic microwire and a method of anisotropy coefficient estimation

A model of head-to-head domain wall in the cylindrical amorphous ferromagnetic microwire is proposed by treating a class of exact particular solutions of Landau-Lifshitz-Gilbert equation in cylindrical coordinates, which are obtained for appropriate boundary conditions. It is shown that both the magnetic anisotropy coefficient value in the center of cross-section and the rate of its value change along the radius directly determine the domain wall structure. A flexural planar domain wall is visualized and analyzed under the influence of various parameters of the microwire. A method of anisotropy coefficient estimation is developed: the derived formula for mobility is used to evaluate values of anisotropy coefficient of the wire near its symmetry axis, the length of the head-to-head domain wall can be used for evaluation of radial dependence of anisotropy coefficient. For extraction of anisotropy coefficient the dynamic properties of the head-to-head domain wall propagation are investigated experimentally for microwires with different anisotropy coefficients: in stressed state and after partially stress removed state. The theory fit the measurements with linear dependence of the velocity on the magnetic field. The particular case of planar domain wall, corresponding to radial independent anisotropy coefficient, is also shown for a comparison.

Dynamics of Domain Walls in a Cylindrical Amorphous Ferromagnetic Microwire with Magnetic Inhomogeneities

Dynamics of Domain Walls in a Cylindrical Amorphous Ferromagnetic Microwire with Magnetic Inhomogeneities

Dynamics of domain walls in a cylindrical amorphous ferromagnetic microwire with magnetic inhomogeneities

Исследована динамика доменной стенки в магнитном сердечнике тонких аморфных бистабильных микропроводов круглого сечения в стеклянной оболочке, содержащих продольные неоднородности. Используется системный аналитический подход к задаче поиска частных решений непрерывной модели Гейзенберга, для чего используются уравнения Ландау-Лифшица-Гильберта. Установлена связь между структурой материала с дефектами и подвижностью доменной стенки, которая объясняет некоторые экспериментальные данные. Для заданного распределения дефектов в продольном направлении изучается влияние дефектов на распространение доменных стенок в бистабильных микропроводах в стеклянной оболочке. Получены новые ключевые формулы для скорости и ускорения доменной стенки на основе учета усредненного распределения дефектов.

Ferromagnetic Microwire Systems as a High-Gradient Magnetic Field Source for Magnetophoresis

The use of amorphous ferromagnetic microwires has potential for applications in biomedicine and biophysics. Microwire arrays create magnetic fields that are characterized by strong spatial gradients. A system of ferromagnetic microwires with magnetizations across the diameter may efficiently accumulate paramagnetic particles along the wire due to forced diffusion. For typical system parameters, the particles concentration at the wire surface increases more than twice for a characteristic time of 30 s. A pair of closely spaced microwires with diametric magnetizations (referred to as a dipole pair) yields a unique potential landscape with a two-dimensional minimum. The possibility of levitation of diamagnetic particles just above the dipole pair array was numerically demonstrated.

Measurement of the Stiffness of Spin Waves in Amorphous Ferromagnetic Microwires by the Small-Angle Neutron Scattering Method

The spin-wave stiffness of a ferromagnetic microwire in the form of an amorphous Fe77.5Si5.5B15 strand with a diameter of 10 μm in a glass shell has been measured by the method of small-angle scattering of polarized neutrons. According to the quadratic dispersion relation for the ferromagnet, neutron scattering by spin waves is concentrated inside a cone with a cutoff angle θC. The cutoff angle θC has been determined by comparing the antisymmetric contribution to the intensity of scattering of polarized neutrons and a model function for a magnetic field H varied from 3.40 to 41 mT. The cutoff angle θC decreases according to the formula $$\theta _C^2(H) = \theta _C^2 - \left( {g{\mu _B}H + \Delta } \right){\theta _0}/{E_i},\,\;\;{\rm{where}}\,\,{\theta _0} = \,{\hbar^2}/(2A{m_n})$$. The stiffness of spin waves and the energy gap in the spectrum of spin waves in the Fe77.5Si5.5B15 ferromagnetic microwire at room temperature determined from the field dependence are meV $$\theta _C^2(H)$$ are A =82(3) meV A2 and Δ=0.048(2) meV, respectively. It has been shown that this method for the measurement of the stiffness of spin waves can be successfully used in compact (with low and moderate fluxes) pulsed neutron sources based on accelerators.

Magnetic Anisotropy and Super-Sensitive Stress-Magnetoimpedance in Microwires with Positive Magnetostriction

In glass-coated Co71Fe5B11Si10Cr3 amorphous ferromagnetic microwires subjected to current annealing, a record sensitivity of the magnetoimpedance (MI) to mechanical tensile stresses (stress MI) up to 100% at 100 MPa in the absence of additional magnetic bias fields is achieved. The current annealing, combining the effect of Joule heating and a circular magnetic field, induces a specific helicoidal/circular-type magnetic anisotropy and, thus, allows one to control the behavior of the MI and stress MI, making the wires more suitable for use in sensor devices. As a result of changing the direction of the easy anisotropy axis, external mechanical stresses lead to a change in the direction of the static magnetization, which causes an increase in the sensitivity of stress MI.