Ferromagnetic Microwires Research Articles

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.

Effect of chemical ordering annealing on superelasticity of Ni–Mn–Ga–Fe ferromagnetic shape memory alloy microwires**Project supported by the National Natural Science Foundation of China (Grant Nos. 51701099, 51801044, and 51671071), the Natural Science Foundation of Heilongjiang Province of China (Grant No. LH2019E091), and Fundamental Research Funds in Heilongjiang Provincial Universities, China (Grant No. 135409320). Thanks to the help of Technology Innovation

Ni50Mn25Ga20Fe5 ferromagnetic shape memory alloy microwires with diameters of ∼ 30–50 μm and grain sizes of ∼ 2–5 μm were prepared by melt-extraction technique. A step-wise chemical ordering annealing was carried out to improve the superelasticity strain and recovery ratio which were hampered by the internal stress, compositional inhomogeneity, and high-density defects in the as-extracted Ni50Mn25Ga20Fe5 microwires. The annealed microwires exhibited enhanced atomic ordering degree, narrow thermal hysteresis, and high saturation magnetization under a low magnetic field. As a result, the annealed microwire showed decreased superelastic critical stress, improved reversibility, and a high superelastic strain (1.9%) with a large recovery ratio (> 96%). This kind of filamentous material with superior superelastic effects may be promising materials for minor-devices.

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.

A magnetic sensor using a 2D van der Waals ferromagnetic material

Two-dimensional (2D) van der Waals ferromagnetic materials are emerging as promising candidates for applications in ultra-compact spintronic nanodevices, nanosensors, and information storage. Our recent discovery of the strong room temperature ferromagnetism in single layers of VSe2 grown on graphite or MoS2 substrate has opened new opportunities to explore these ultrathin magnets for such applications. In this paper, we present a new type of magnetic sensor that utilizes the single layer VSe2 film as a highly sensitive magnetic core. The sensor relies in changes in resonance frequency of the LC circuit composed of a soft ferromagnetic microwire coil that contains the ferromagnetic VSe2 film subject to applied DC magnetic fields. We define sensitivity as the slope of the characteristic curve of our sensor, df0/dH, where f0 is the resonance frequency and H is the external magnetic field. The sensitivity of the sensor reaches a large value of 16 × 106 Hz/Oe, making it a potential candidate for a wide range of magnetic sensing applications.

Design and X-Band electromagnetic response of single negative metacomposite containing periodic curved Co-based ferromagnetic microwires

Metamaterials possess attractive electromagnetically left-handed properties yet their nature as an artificial structure rather than a material restricts their further applications. In this article we propose to use Co-based ferromagnetic microwires as periodical metamaterial units interweaved into a fabric to realize a “metacomposite” for steering wave propagation. By introducing ferromagnetic microwires in quartz fabric at three curvatures and periodic lengths, the electromagnetic response and microwave behaviors on both horizontally- and vertically-arranged directions were presented and investigated. Tensile behaviors of metacomposites with different ferromagnetic microwire morphologies were monitored by non-contact full field strain measurement system. At X band (8.2–12.4 GHz), metacomposites containing vertically-arranged ferromagnetic microwires show negative permittivity due to the dielectric resonance of microwire arrays. The dielectric response of metacomposites conformed to Lorentz-oscillator mode, behaving similarly to diluted plasma. When ferromagnetic microwires reached the lowest periodic curved length 2.5 mm with the highest curvature was obtained, the metacomposites presented the maximum microwave absorption of 34% and tensile stress of 273 MPa. The incorporation of ferromagnetic microwires exerts trivial influence on the mechanical properties yet homogenizes the strain and reduces the stress concentration on metacomposites. The metacomposite with a periodic curved length of 7.5 mm has less interweaving points and the highest surface float length, therefore achieving the maximum tensile strength of 458 MPa. The single negative metacomposites containing ferromagnetic microwires are featured with excellent structural properties and amenable microwave left-handed properties in controlling wave-propagating behavior, which is of practical engineering significance in structural health monitoring, sensing and stealth applications.

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.

Macroscopic Modeling of Magnetic Microwires for Finite Element Simulations of Inductive Components

New compound magnetic material based on parallel continuous ferromagnetic microwires (e.g., based on cobalt) embedded in a body made of polymeric material can potentially offer significant mechanical advantages over well-known fragile ferrite in some applications where the magnetic material has to withstand mechanical vibrations. The diameter of the magnetic microwires is minimal (3–60 $\mu$ m) compared to the rest of the dimensions (80–300 mm) and the number of microwires is in the order of 1000 s. It requires extremely fine meshes, then brute force simulation by the finite element method is not possible. In this article, a method to overcome this limitation is proposed, which is based on the substitution of the original material by a homogenous material that behaves, in a macroscopic sense, as the compound material. The physical properties of the homogeneous material are obtained in different spatial directions, due to the inherent anisotropy of the compounded magnetic component, through analytical equations.

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.

Protective shielding fabric materials on the base of ferromagnetic microwire

The article presents the protective and operational characteristics of the developed protective fabric from electromagnetic radiation. The article proposes a technological scheme for the production of tissue that protects against electromagnetic radiation. At the heart of this fabric, it is proposed to use a nanostructured ferromagnetic microwire in a glass shell. It is determined that the protective characteristics of the fabric (screening and reflection coefficients, surface resistance) will depend on the following main factors: chemical composition of the microwire; diameter of the microwire; the number of cores of a microwire in a complex thread; the number of complex threads in the warp and weft systems.

Measurement of the Parameters of Ferromagnetic Microwires in a Frequency Range from 0.1 to 20 GHz

Ferromagnetic microwires are widely applied in the ultrahigh frequency engineering. In this work, a system on the basis of a ZVA-67 vector network analyzer which makes it possible to measure the parameters of ferromagnetic resonance of microwires in a frequency range from 0.1 to 14 GHz is proposed. The impedance of FeCoNi/CuBe and CoFeSiB microwires is approximated using the values of the components of the main diagonal of the magnetic susceptibility tensor. The proposed method makes it possible to find interesting characteristic features of the electromagnetic properties of microwires in the regions of frequencies and magnetic fields where ferromagnetic resonance is observed.

Ferromagnetic Glass-Coated Microwires for Electromagnetic Shielding for Medical Application

Ferromagnetic Glass-Coated Microwires for Electromagnetic Shielding for Medical Application

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.

Core-shell ferromagnetic microwires extracted from PrDyFeCoB and GdPrDy(FeCo)B melts

The α-Fe core/PrDy-FeCo-B(48 at.%)α-Fe(52 at.%) shell and GdPrDy(FeCo)B microwires were grown by pendant drop melt (PDM) extraction technique. Single core–shell microwires of ~80–100 μm diameter and 2–20 mm length manifest rectangular hysteresis loops corresponding to ~100 Oe switching magnetic fields. Bistability of the microwires relates to single domain state of the α-Fe inner core revealed by scanning electron microscopy (SEM). Rare-earth amorphous PrDy-FeCo-B shell of the microwire scanned by magnetic force microscope (MFM) possesses magnetization reversal nuclei corresponding to the α-Fe inclusions. Interwire magnetic dipole interaction and scattering of microwire size change shape of the magnetic hysteresis loop and increase coercive field up to 983 Oe, in chaotic ensembles of the core–shell microwires. The GdPrDy(FeCo)B microwires of the same sizes with no Fe core possess “butterfly” type of the hysteresis loop of high coercivity ~20 kOe.

Microstructure investigation of r.f. current annealed FINEMET cold drawn microwires by UHR-TEM

The microstructure of FINEMET (Fe73.5Nb3Cu1Si13.5B9, at %) ferromagnetic microwires with diameters of 30 µm obtained by cold drawn of 120 µm thicker conventional amorphous microwires followed by radio frequency current annealing has been investigated by ultra-high resolution transmission electron (UHR-TEM) microscopy. The cold drawn microwires (CDWs) were annealed by radio frequency current of 375 mA@10MHz and 750 mA@10MHz, respectively, for 10 minutes to achieve cold drawn microwires with nano-crystalline structure. The specimens for UHR-TEM investigation were prepared in the shape of lamella using Focus Ion Beam microscope. For each annealed CDNWs were obtained two lamella one from the edge of microwire and another one from the center of the wire. Each specimen has been examined by transmission electron microscopy (TEM) using a Libra200MC microscope operated at 200kV through the bright-field and dark-field TEM, HR-TEM, HAADF STEM and EDX method. Electron diffraction patterns are interpreted using the computer programs SingleCrystal® and JEMS®. Mean grain size is measured using ImageJ software and making a geometrical correction for film thickness. The cold drawn microwires annealed at 350mA are largely amorphous, although containing occasional Fe3Si regions of short-range order as presented in Figure 1 (a). The cold drawn microwires annealed at 750mA present a nano-crystalline structures, with all nano-grains appearing to be of the bcc α-Fe(Si) structure as shown in Figure 1 (b). The estimated number density of nano-grains is 4.8 x 1023, which corresponds to an estimated phase fraction of 25 vol.% for a nano-grain radius of 5 nm. Line-scan EDX shows no particularly striking deviation from a homogenous distribution of elements for nanocrystalline sample, while a clustering behavior of elements for amorphous sample was observed.

Textile structured metacomposites with tailorable negative permittivity under X and Ku band

The metacomposites with tailorable negative permittivity including periodic interweaving ferromagnetic mircowires were fabricated by weaving and resin transfer molding methods. By manipulating the alignment direction, periodic curved length, spacing between ferromagnetic microwires for adjusting complex permittivity and permeability, the electromagnetic wave propagation of as-prepared metacomposites under X and Ku bands were evaluated and investigated by experiment and simulation. For metacomposites composed of vertically arranged microwires, for both 1 mm and 0.5 mm spacing, the permittivity turned to negative in certain frequency bands. The simultaneous existence of short periodic curved length and spacing benefits the broadening of frequency band under which metacomposites exhibits single-negative behavior. Significant transmission windows are observed due to negative permittivity occurring at plasma frequency. The simulation results show major loss for the textile structured metacomposites under X and Ku bands derives from electric loss, and small periodic curved length tends to form uniform power loss distribution.

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.

Erratum to: Matrices of Ferromagnetic Microwires for the Control of Cellular Dynamics and Localized Delivery of Medicines

Erratum to: Matrices of Ferromagnetic Microwires for the Control of Cellular Dynamics and Localized Delivery of Medicines

Scattering of Microwaves by a Passive Array Antenna Based on Amorphous Ferromagnetic Microwires for Wireless Sensors with Biomedical Applications.

Co-based amorphous microwires presenting the giant magnetoimpedance effect are proposed as sensing elements for high sensitivity biosensors. In this work we report an experimental method for contactless detection of stress, temperature, and liquid concentration with application in medical sensors using the giant magnetoimpedance effect on microwires in the GHz range. The method is based on the scattering of electromagnetic microwaves by FeCoSiB amorphous metallic microwires. A modulation of the scattering parameter is achieved by applying a magnetic bias field that tunes the magnetic permeability of the ferromagnetic microwires. We demonstrate that the OFF/ON switching of the bias activates or cancels the amorphous ferromagnetic microwires (AFMW) antenna behavior. We show the advantages of measuring the performing time dependent frequency sweeps. In this case, the AC-bias modulation of the scattering coefficient versus frequency may be clearly appreciated. Furthermore, this modulation is enhanced by using arrays of microwires with an increasing number of individual microwires according to the antenna radiation theory. Transmission spectra show significant changes in the range of 3 dB for a relatively weak magnetic field of 15 Oe. A demonstration of the possibilities of the method for biomedical applications is shown by means of wireless temperature detector from 0 to 100 °C.