As-prepared Microwires Research Articles

Optimization of Giant Magnetoimpedance Effect of Amorphous Microwires by Postprocessing

Magnetic microwires with amorphous structures can present a unique combination of excellent magnetic softness and giant magnetoimpedance (GMI) effects together with reduced dimensions and good mechanical properties. Such unique properties make them suitable for various technological applications. The high GMI effect, observed in as-prepared Co-rich microwires, can be further optimized by postprocessing. However, unexpected magnetic hardening and a transformation of the linear hysteresis loop into a rectangular loop with a coercivity on the order of 90 A/m were observed in several Co-rich microwires upon conventional annealing. Several routes to improve magnetic softness and GMI effect in Fe- and Co-rich magnetic microwires are provided. We observed that stress annealing could remarkably improve the magnetic softness and GMI ratio of Co-rich microwires. Thus, almost unhysteretic loops with a coercivity of 2 A/m and a magnetic anisotropy field of about 70 A/m are achieved in Co-rich microwires stress annealed at appropriate conditions. The observed change in hysteresis loops and the GMI effect is explained by stress-annealing-induced anisotropy, which is affected by the stresses applied during annealing and by the annealing temperature. While as-prepared Fe-rich amorphous microwires present a low GMI effect, appropriate postprocessing (annealing and stress annealing) allows for a remarkable GMI ratio improvement (an order of magnitude). The evaluated dependence of the maximum GMI ratio on frequency allows the identification of the optimal frequency band for the studied samples. The origin of stress-annealing-induced anisotropy and related changes in hysteresis loops and the GMI effect are discussed in terms of the relaxation of internal stresses, “back-stresses”, as well as structural anisotropy.

Optimization of Magnetoimpedance Effect and Magnetic Properties of Fe-Rich Glass-Coated Microwires by Annealing.

As-prepared Fe-rich microwires with perfectly rectangular hysteresis loops present magnetization reversal through fast domain wall propagation, while the giant magnetoimpedance (GMI) effect in Fe-rich microwires is rather low. However, the lower cost of Fe-rich microwires makes them attractive for magnetic sensors applications. We studied the effect of conventional (furnace) annealing and Joule heating on magnetic-propertied domain wall (DW) dynamics and the GMI effect in two Fe microwires with different geometries. We observed that magnetic softness, GMI effect and domain wall (DW) dynamics can be substantially improved by appropriate annealing. Observed experimental results are discussed considering the counterbalance between the internal stresses relaxation and induced magnetic anisotropy associated with the presence of an Oersted magnetic field during Joule heating.

Effect of temperature on magnetic properties and magnetoimpedance effect in Fe-rich microwires

Herein, the temperature dependence of hysteresis loops and the Giant magnetoimpedance, GMI, effect of amorphous as-prepared and stress-annealed FeSiBC microwires have been thoroughly analyzed. We observed a remarkable improvement of GMI ratio and modification of hysteresis loops from rectangular to inclined with increase in temperature for as-prepared FeSiBC microwires. Observed changes have almost completely reversible character. On the other hand, rather different behavior is observed in stress-annealed FeSiBC microwires: a substantial GMI ratio improvement is observed in stress-annealed FeSiBC microwires. However, a decrease in GMI effect is observed with temperature increasing. Observed experimental results are discussed considering relaxation of internal stresses upon heating, Hopkinson effect and modification of the thermal expansion coefficients upon heating.

Outstanding intrinsic two-way shape memory effect of the Ni54.71Mn22.14Ga23.15 oligocrystalline shape memory microwire

The shape memory effect of the Ni54.71Mn22.14Ga23.15 oligocrystalline microwire was investigated. The microwire was expected to exhibit an outstanding two-way shape memory effect due to the directional internal stress induced in the preparation. The results show that the microstructure of the as-prepared Ni54.71Mn22.14Ga23.15 microwire was mainly oriented martensites at room temperature. An intrinsic two-way shape memory strain of 8.8% (±0.2%) in the as-prepared microwire was acquired in the process of cooling and heating with no applied stress. A shape memory strain of 14.4% (±0.2%) was obtained under the constant stress of 10 MPa. The isothermal tensile tests were carried out on the microwire in the temperature range of 383–463 K and the recoverable tensile strains were over 13%. The microwire after superelastic training maintained a two-way shape memory strain of 7.3% (±0.2%) and a work output of 31 J/cm3. The shape memory effect of the microwire in this work displays prominent advantages in the reported shape memory alloys, mainly in the aspects of larger intrinsic shape memory strain and higher work output under relatively lower stress with the operating window around room temperature.

Development of Magnetically Soft Amorphous Microwires for Technological Applications

Amorphous magnetic microwires can be suitable for a variety of technological applications due to their excellent magnetic softness and giant magnetoimpedance (GMI) effect. Several approaches for optimization of soft magnetic properties and GMI effect of magnetic microwires covered with an insulating, flexible, and biocompatible glass coating with tunable magnetic properties are overviewed. The high GMI effect and soft magnetic properties, achieved even in as-prepared Co-rich microwires with a vanishing magnetostriction coefficient, can be further improved by appropriate heat treatment (including stress-annealing and Joule heating). Although as-prepared Fe-rich amorphous microwires exhibit low GMI ratio and rectangular hysteresis loops, stress-annealing, Joule heating, and combined stress-annealed followed by conventional furnace annealing can substantially improve the GMI effect (by more than an order of magnitude).

Wavelength tunable single-mode lasing from cesium lead halide perovskite microwires

Cesium lead halide perovskites have shown great potential applications in photoelectric devices because of their high quantum efficiency, good stability, and tunable bandgap. Herein, we prepared CsPbBr3 microwires with a high crystal quality, smooth surface, and rectangular cross section via the solution method. The as-prepared microwires presented a high quality whispering gallery mode lasing with a low threshold of 9.1 μJ cm−2 and a high quality factor of ∼3000. Furthermore, we obtained the alloys of CsPbClxBr3−x (0 < x < 2) microwires through the gas-phase anion exchange method and realized the wavelength tunable single-mode lasing emission ranging from ∼546.8 nm to ∼468.0 nm. This work will expand the practical application of lead halide perovskites in spectrograph, optical communication, and in-chip photoelectric devices.

Cylindrical micro and nanowires: Fabrication, properties and applications

The state of the art in cylindrical nano and micro wires is reviewed with particular emphasis on the latest research trends. We analyze some of the key properties for prospective applications including magnetic anisotropy and micromagnetic structure, spin-caloritronics, domain wall dynamics and its control by transverse magnetic field and induced anisotropy, high frequency impedance and magnetic control of the electric polarizability, shape-memory and magnetocaloric effects in Heusler alloys wires. Cylindrical nanowires present specific magnetic domain configurations as complex vortex and transverse domains while the magnetization reversal typically involves propagation of Bloch-point domain walls. Such magnetic behavior offers new perspectives for applications in advanced technologies including spintronics, logic devices and novel magnetic recording media, functionalization and bioengineering and sensor devises. In particular, rapidly solidified glass-coated amorphous nanowires and submicron wires which constitute a novel class of ultrathin soft magnetic materials are attractive for future micro and nano sensors.Amorphous and nanocrystalline microwires prepared by rapid quenching from the melt can present quite peculiar magnetic properties, like spontaneous magnetic bistability associated with single and large Barkhausen jump and magnetoimpedance effect. Magnetic properties of amorphous microwires are related to the value and sign of the magnetostriction constant since the magnetoelastic anisotropy is one of the main sources of the magnetic anisotropy. As-prepared microwires with positive magnetostriction constant show generally rectangular hysteresis loops and fast domain wall propagation. In the case of low and negative magnetostriction, the wires demonstrate inclined hysteresis loops and large magnetoimpedance. To refine the magnetic structure, the easy anisotropy can be adjusted by annealing in the presence of a magnetic field and/or mechanical stress. Thus, the magnetic bistability in negative magnetostriction wires can be induced by annealing. Minimizing the magnetoelastic anisotropy either by adjusting the chemical composition with a low magnetostriction coefficient or by heat treatment is an appropriate route for enhancing the domain wall velocity. Tailoring the magnetic anisotropy by stress-annealing is also a promising method of the optimization of the domain wall dynamics in magnetic microwires.Soft magnetic properties and tunable magnetic structure of amorphous microwires are responsible for the magnetoimpedance effect, which preserves a high sensitivity up to GHz frequencies. This opens up novel applications based on the electric polarization of a finite-length microwire depending on the wire surface impedance near the antenna resonance, including embedded wireless sensing elements, self-sensing composites and selective microwave materials.Heusler alloys demonstrate the huge variety of physical properties that can be obtained by simple change in composition. Naturally, the efforts have been made to produce Heusler-based nano and micro wires to take advantage of variety of their physical properties in a miniature form. In this review, the emphasis is made on Heusler alloy glass-coated microwires.

Giant high temperature superelasticity in Ni53Mn24Ga21Co1Cu1 microwires

Ni-Mn-Ga is commonly used as a room temperature shape memory alloy. With the doping of Co and Cu, its phase transformation temperature increased to around 500 K, which can be used as high temperature shape memory alloys, and the superelasticity and shape memory strains are improved as well. Here, giant recoverable strain 16.3% is reported in a Heusler type Ni53Mn24Ga21Co1Cu1 microwire, prepared by rapid solidification via the Taylor-Ulitovsky method, with a diameter of 140 μm. Within a 150 K temperature range, the microwire maintains superelastic property of more than 10%. It has high cycle stability and the superelasticity remains almost unchanged after 100 cycles test at 523.15 K. It was also found that the energy loss density of the heat treated microwire is about twice than that of as-prepared microwire.

Stress-induced magnetic anisotropy enabling engineering of magnetic softness of Fe-rich amorphous microwires

Stress-annealing allows considerably modify magnetic properties of Fe-rich glass-coated microwires. Varying the stress-annealing conditions (temperature, time and stress applied during the annealing) we can observe either remarkable improvement of magnetic softness and giant magnetoimpedance (GMI) effect. Observed changes have been attributed to the transverse magnetic anisotropy. An improvement of the circumferential permeability in the surface layer of metallic nucleus is evidenced from observed magnetic softening and remarkable GMI effect rising. We assumed that stress-annealing leads to an increase in the outer domain sheath with transverse magnetic anisotropy rise in expense of inner axially magnetized core typically existing in as-prepared Fe-rich microwires. Consequently, stress annealing enabled us to design the magnetic anisotropy distribution beneficial for optimization of the GMI effect and magnetic softness of Fe-rich magnetic microwires.

Controlling the domain wall dynamics in Fe-, Ni- and Co-based magnetic microwires

Abstract We studied influence of post-processing (annealing and stress-annealing) on domain wall dynamics in Fe-, Ni- and Co-based magnetic microwires with spontaneous and induced magnetic bistability. As-prepared Co-based microwires with low and negative magnetostriction present linear hysteresis loops. Magnetic bistability in Co-based microwires has been induced by annealing. Minimizing magnetoelastic anisotropy either by adjusting the chemical composition with a low magnetostriction coefficient or by heat treatment is an appropriate route for the domain wall dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of domain wall velocity and hence is a promising method allowing optimization of the DW dynamics in magnetic microwires. The beneficial influence of stress-annealing on the DW dynamics is explained considering an increase in the volume of outer domain shell with transverse magnetization orientation in expense of decrease in the radius of the inner axially magnetized core. Such transverse magnetic anisotropy can affect the DW dynamics in similar way as the applied transverse magnetic field and hence is beneficial for the DW dynamics optimization. Thus, stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Co-rich microwires with magnetic bistability induced by annealing present a considerable enhancement in the DW velocity upon applied tensile stress: exactly the opposite to the case of magnetic microwires with spontaneous magnetic bistability. Observed dependence has been explained considering decrease in the magnetostriction coefficient under effect of the applied stress.

Direct Magnetoelectric Effect in a Sandwich Structure of PZT and Magnetostrictive Amorphous Microwires.

The magnetoelectric (ME) response in a trilayer structure consisting of magnetostrictive Fe77.5B15Si17.5 amorphous microwires between two piezoelectric PZT (PbZr0.53Ti0.47O3) layers was investigated. Soft magnetic properties of wires make it possible to operate under weak bias magnetic fields below 400 A/m. Enhanced ME voltage coefficients were found when the microwires were excited by ac magnetic field of a frequency of 50–60 kHz, which corresponded to the frequency of electromechanical resonance. The as-prepared microwires were in a glass coat creating a large thermoelastic stress and forming a uniaxial magnetic anisotropy. The effect of glass-coat removal and wire annealing on ME coupling was investigated. The glass coat not only affects the wire magnetic structure but also prevents the interfacial bonding between the electric and magnetic subsystems. However, after its removal, the ME coefficient increased slightly less than 10%. Refining the micromagnetic structure and increasing the magnetostriction by stress release during wire annealing (before or after glass removal) strongly increases the ME response up to 100 mV/(cm × Oe) and reduces the characteristic DC magnetic field down to 240 A/m. Although the achieved ME coefficient is smaller than reported values for multilayered films with layers of PZT and soft magnetic alloys as Metglass, the proposed system is promising considering a small volume proportion of microwires.

Routes for optimization of giant magnetoimpedance effect in magnetic microwires

The objective of this report is to present the route of development of magnetically soft thin wires for applications in magnetic sensors. We present our experimental study of the Giant magnetoimpedance (GMI) effect of magnetic microwires prepared using the Taylor-Ulitovsky technique. We observed that the GMI effect and magnetic softness of microwires can be tailored either by controlling magnetoelastic anisotropy of as-prepared microwires or by controlling their internal stresses and structure with heat treatment. High GMI effect has been observed and discussed.

Soft magnetic microwires for sensor applications

We provide an overview of the routes allowing the optimization of magnetic softness, giant magnetoimpedance (GMI) effect and domain wall dynamics in one of the families of magnetic microwires: glass –coated microwires prepared using Taylor-Ulitovsky method. The magnetic properties of as-prepared microwires are determined mostly by the magnetoelastic anisotropy. Conventional annealing allows a considerable improvement of the domain wall dynamics in Fe-rich microwires and a slight decrease of the coercivity, however, remarkable magnetic hardening is observed after conventional furnace annealing of Co-rich microwires. Stress annealing of Fe-rich microwires allows a considerable magnetic softening and GMI effect enhancement and even more remarkable improvement of the domain wall dynamics. In Co-rich microwires stress-annealing allows the improvement of GMI effect and even the induction of transverse magnetic anisotropy at high enough annealing temperature. However, the highest GMI effect is observed for stress-annealed Co-rich microwires which present rectangular hysteresis loops. Consequently, annealed Co-rich microwires can present both, fast domain wall propagation and GMI effect.Observed induced anisotropy and related changes of the magnetic properties are discussed considering the internal stresses relaxation, “back-stresses” and circumferential magnetic field during proposed post-processing.Consequently, correctly designed post-processing enabled us to design the magnetic anisotropy distribution beneficial for the optimization of the GMI effect and the domain wall dynamics in magnetic microwires.

Development of Magnetic Microwires for Magnetic Sensor Applications.

Thin magnetic wires can present excellent soft magnetic properties (with coercivities up to 4 A/m), Giant Magneto-impedance effect, GMI, or rectangular hysteresis loops combined with quite fast domain wall, DW, propagation. In this paper we overview the magnetic properties of thin magnetic wires and post-processing allowing optimization of their magnetic properties for magnetic sensor applications. We concluded that the GMI effect, magnetic softness or DW dynamics of microwires can be tailored by controlling the magnetoelastic anisotropy of as-prepared microwires or controlling their internal stresses and domain structure by appropriate thermal treatment.

The effect of heat treatment on magnetic and thermal properties of Finemet-type ribbons and microwires

Abstract We studied the influence of annealing conditions on magnetic and thermal properties of Finemet-type alloys. The evolution of the Curie temperature, Tc, and the change of heat capacity in the vicinity of this magnetic transformation, ΔCpTc, were investigated using Differential Scanning Calorimetry, DSC. Relaxation of atomic structure of amorphous phase during the annealing was accompanied by an increase in Tc and decrease in ΔCpTc. Two relaxation processes with different mechanisms take place in amorphous state: topological ordering and chemical ordering. The study of the kinetics of relaxation process allows to estimate the apparent values of activation energy of both relaxation processes: 29 and 87 kJ/mol for ribbon, 37 and 112 kJ/mol for microwire. Precipitation of α-Fe nanocrystallites in amorphous phase leads to gradual degradation of the Tc peak. The Tc peak reduction is correlated to decrease of the amorphous phase as well as lowering of its magnetostriction. The influence of internal stress on the position and shape of the Curie peak was determined by comparing data for the ribbon-shaped alloys and glass coated microwires. Considerable magnetic softening and giant magnetoimpedance effect under heat treatment is observed in the studied Finemet-type microwires. Changes in magnetic properties after heating are associated with devitrification and stresses relaxation. We also study the influence of internal stresses induced by glass coating on the magnetic properties of as-prepared and annealed microwires. The results confirm the previously made conclusion that changes in the thermal and magnetic properties of Finemet-type alloys during heating are interrelated, since they are reflections of the fundamental characteristics of the material.

High frequency giant magnetoimpedance effect of a stress-annealed Fe-rich glass-coated microwire

Processing by stress-annealing (450 MPa, 300 °C, 1 h) the glass-coated microwire of Fe75B9Si12C4 composition a macroscopic magnetic anisotropy with a circular component is developed. This anisotropy very significantly improves the giant magnetoimpedance (GMI) effect with respect to the observed in the as-prepared microwire. The analysis of the GMI response as a function of the frequency (10–1000 MHz) opens new lights to understand the distribution of the magnetic anisotropy inside the glass-coated microwire.We have investigated the GMI response of the stress-annealed Fe75B9Si12C4 glass-coated microwire. From the frequency dependence of the GMI we have analyzed the distribution of the magnetic anisotropy inside the metallic nucleus obtaining good agreement with the average value of the anisotropy field deduced from the hysteresis loop of the bulk.From measured magnetic field dependences of GMI ratio we evaluated the frequency and magnetic field dependences of the penetration depth. We found that the minimum penetration depth of Fe75B9Si12C4 microwire decreases from about 1.5 μm down to 0.8 μm after stress annealing.Obtained dependences demonstrate that the minimum penetration depth value as well as the frequency and magnetic field dependences are considerably affected by the stress-annealing.

Stress dependence of the magnetic properties of glass-coated amorphous microwires

We studied the effect of applied tensile stresses on magnetic properties of Fe- and Co-rich amorphous glass-coated microwires. Rising of magnetic anisotropy field upon tensile stress in Co-rich glass-coated microwires is described by a linear dependence. Furthermore, decrease of magnetic susceptibility upon tensile stress is observed in Co-rich microwires. A monotonous increase in the coercivity and the switching field upon tensile applied stress is observed for as-prepared Fe-rich microwire. Stress induced magnetic bistability consisting of transformation of hysteresis and onset of rectangular hysteresis loop upon tensile stress, σ, of about 22.5 MPa is observed in stress-annealed Fe-rich microwires. Such stress-induced magnetic bistability results in considerable growing of coercivity and remanent magnetization in stress-annealed Fe-rich microwires. The rising in the coercivity and the switching field upon applied tensile stresses in stress-annealed Fe-rich microwires with stress induced magnetic bistability (at σ > 22.5 MPa) is roughly described by the σ½ dependence, as previously reported for the wires with spontaneous magnetic bistability. Consequently, stress-annealing of Fe-rich microwire allows beneficial enhancement of the stress dependence of coercivity. Observed dependencies are discussed considering stress dependence of the magnetostriction coefficient in Co-rich glass-coated microwires, internal stresses redistribution and domain structure rearrangement in stress-annealed Fe-rich microwires upon applied tensile stresses.

Magnetic properties of “thick” glass-coated Fe-rich microwires

We report on preparation and magnetic properties of Fe71.7B13.4Si11Nb3Ni0.9 glass-coated microwire with metallic nucleus diameter d = 103 μm and total diameter D = 158 μm prepared by Taylor-Ulitovsky method. Amorphous structure of as-prepared microwires is confirmed by X-ray diffraction. As-prepared glass-coated microwires present relatively high GMI effect (about 50%) and relatively low coercivity (about 25 A/m). Additionally, as-prepared sample present rectangular hysteresis loop and fast single domain wall propagation with domain wall mobility of about 11,9 m2/As. After annealing we observed considerable improvement of the GMI ratio (from 50% up to 100%). Observed GMI effect improvement has been attributed to the stresses relaxation. From aforementioned studies we can conclude that the Taylor-Ulitovsky technique allows us to obtain thick ferromagnetic microwires with good magnetic properties and GMI effect suitable for industrial applications.

Fabrication of morphology-controlled and highly-crystallized perovskite microwires for long-term stable photodetectors

In this work, highly crystallized and lengths up to a centimeter organic-inorganic hybrid perovskite CH3NH3PbI3 (MAPbI3) microwires (MWs) have been prepared via a solution-based blade coating and slow solvent evaporation method. And a two-step growth mechanism was proposed to explain the formation and growth of the MAPbI3 MWs. Further, the as-prepared MWs were used to fabricate photodetectors and their photoresponse characteristics were tested and detailedly analyzed. The results reveal that the devices presented stable and repeatable photocurrent responses. A high on/off photocurrent ratio of 0.84 × 104, a photoresponsivity of 0.04 A/W, a specific detectivity of 0.6 × 1012 Jones, and a fast response speed of 178/173 μs were realized in the prepared MAPbI3 photodetectors. More importantly, even without encapsulation, the proposed photodetectors demonstrate remarkable operation stability, above 80% of the photocurrent has been retained after a long running time (50,000 s, 45–55% humidity). After 60 days storage without encapsulation in air ambient, the proposed photodetectors can be efficiently sustained, demonstrating a strong ability to resist the water and oxygen degradation, greatly superior to reference photodetectors constructed with MAPbI3 thin films. This work opens up an exciting opportunity for using MAPbI3 MWs for high-performance and low-cost photodetectors applications.

Engineering of Magnetic Properties of Co- and Fe-Rich Microwires

We present our experimental results on optimization of the magnetic softness, domain wall (DW) dynamics, and giant magnetoimpedance (GMI) effect of Fe- and Co-rich microwires. It is found that the as-prepared Co-rich microwires possess much higher GMI effects and linear hysteresis loop. On the other hand, the magnetic softness and GMI effect of Fe-rich microwires can be improved by stress annealing. In addition, the DW velocity of the microwires can be considerably improved by annealing. The single DW propagation can also be observed in properly annealed Co-rich microwires. These observed dependencies can be attributed to the relaxation of internal stresses after annealing and the interplay of compressive stresses and axial internal stresses after stress annealing.