Fast Domain Wall Propagation Research Articles

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.

Tuning of Magnetoimpedance Effect and Magnetic Properties of Fe-Rich Glass-Coated Microwires by Joule Heating.

The influence of Joule heating on magnetic properties, giant magnetoimpedance (GMI) effect and domain wall (DW) dynamics of Fe75B9Si12C4 glass-coated microwires was studied. A remarkable (up to an order of magnitude) increase in GMI ratio is observed in Joule heated samples in the frequency range from 10 MHz to 1 GHz. In particular, an increase in GMI ratio, from 10% up to 140% at 200 MHz is observed in Joule heated samples. Hysteresis loops of annealed samples maintain a rectangular shape, while a slight decrease in coercivity from 93 A/m to 77 A/m, after treatment, is observed. On the other hand, a modification of MOKE hysteresis loops is observed upon Joule heating. Additionally, an improvement in DW dynamics after Joule heating is documented, achieving DW propagation velocities of up to 700 m/s. GMI ratio improvement along with the change in MOKE loops and DW dynamics improvement have been discussed considering magnetic anisotropy induced by Oersted magnetic fields in the surface layer during Joule heating and internal stress relaxation. A substantial GMI ratio improvement observed in Fe-rich Joule-heated microwires with a rectangular hysteresis loop and fast DW propagation, together with the fact that Fe is a more common and less expensive metal than Co, make them suitable for use in magnetic sensors.

Vol4 num4-16 Magnetic properties and applications of glass-coated ferromagnetic microwires

The impact of post-processing on soft magnetic properties and the giant magnetoimpedance (GMI) effect of Fe- and Co-based glass-coated microwires is evaluated. A remarkable improvement of magnetic softness and GMI effect is observed in Fe-rich glass-coated microwires subjected to stress annealing. Frequency dependence of GMI ratio of stress-annealed Fe-rich microwires has been discussed considering frequency dependence of the skin penetration depth, δ, as well as magnetic anisotropy distribution within the metallic nucleus. Annealed and stress-annealed Co-rich microwires present rectangular hysteresis loop and single and fast domain wall propagation. However, Co-based stress-annealed microwires present high magnetoimpedance ratio. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses”.

Domain wall mobility engineering by a perpendicular magnetic field in microwires with a gradient of perpendicular anisotropy

Fast domain wall propagation is a typical feature of amorphous glass-coated microwires with positive magnetostriction. The high domain wall velocity can be effectively tailored either by sample postprocessing or temperature. In this work, we show that the domain wall dynamics can be engineered by a perpendicular magnetic field. We perform the domain wall mobility measurements in microwires with a varying gradient of the perpendicular magnetic anisotropy. It is shown that domain wall mobility is mainly determined by counterplay between the amplitude of perpendicular anisotropy and externally applied perpendicular field. The presence of perpendicular magnetic anisotropy is observed by Scanning electron microscopy. The relation between the maximum applied perpendicular magnetic field, and the wire dimensions are provided based on the measured data.

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.

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.

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.

AC-current-induced magnetization switching in amorphous microwires

We studied the influence of AC current flowing through microwires, on magnetization dynamics. We used a previously developed Sixtus-Tonks modified setup to evaluate the domain wall (DW) velocity within the microwire. However, instead of a magnetizing solenoid, we used a current flowing through the microwire. We observed that the AC current flowing through the annealed Co-rich microwire leads to remagnetization by fast domain wall propagation. The estimated DW velocity was approximately 4.5 km/s, which is similar to and even higher than that reported for the magnetic-field-driven domain wall propagation in Fe- and Co-rich microwires. We measured the DW velocity under tensile stress, and found that the DW velocity decreases under applied stress. An observed DW propagation induced by the current flowing through the microwire is explained considering the influence of an Oersted magnetic field on the outer domain shell. This field has a circular easy magnetization direction and magnetostatic interaction between the outer circumferentially magnetized shell and the inner axially magnetized core.

Current induced domain wall propagation in Co-rich amorphous microwires

We studied the influence of the AC current flowing through the magnetically bistable Co-rich microwire on the magnetization dynamics. We used previously developed Sixtus-Tonks modified set-up for evaluation of the domain wall (DW) velocity within the microwire, but instead of the magnetizing solenoid we used the current flowing through the microwire. We observed that the AC current flowing though the sample produces the remagnetization of the sample by fast domain wall propagation along the microwire. Estimated DW velocity is about 4.5 km/s, being similar and even higher to that reported for the magnetic field driven domain wall propagation in Fe and Co-rich microwires. Observed current induced DW propagation through the microwire we explained considering the magnetostatic interaction between the outer circumferentially magnetized shell and the inner axially magnetized core.

Simultaneous Detection of Giant Magnetoimpedance and Fast Domain Wall Propagation in Co-Based Glass-Coated Microwires

The magnetic properties of as-prepared and annealed amorphous $\text{Co}_{{50}.{69}}{{\text {Fe}}_{{8}.{13}}}{{\text {Ni}}_{{17}.{55}}}{{\text {B}}_{{13}.{29}}}{{\text {Si}}_{{10}.{34}}}$ and glass-coated microwires produced by the Taylor–Ulitovsky technique are investigated systematically. Magnetic-field frequency dependences of magnetoimpedance (MI), domain-wall (DW) velocity, and hysteresis loops were measured. At certain annealing conditions, high MI and fast DW propagation simultaneously coexist. The results suggest criteria for the selection of materials for high-performance magnetic sensors.

Grain size refinement in nanocrystalline Hitperm-type glass-coated microwires

We present a new-Fe38.5Co38.5B18Mo4Cu1 Hitperm glass-coated microwires obtained by Taylor-Ulitovsky technique with nanocrystalline structure consisting of about 23nm of BCC α-FeCo and an amorphous precursors in as-prepared samples. Annealing resulted in a considerable decrease of such nano-grains down to (11nm). Obtained results are discussed in terms of the stress diffusion of limited crystalline growth and the chemical composition. Rectangular hysteresis loops have been observed on all annealed samples that are necessary conditions to obtain fast domain wall propagation. An enhancement of the domain wall velocity as well as mobility after annealing has been obtained due to the structural relaxation of such grains with positive magnetostriction. These structure benefits found in the nanocrystalline Hitperm glass-coated microwires are promising for developing optimal magnetic properties.

Effect of annealing on magnetic properties of nanocrystalline Hitperm-type glass-coated microwires

We studied magnetic properties of Fe38.5Co38.5B18Mo4Cu1 Hitperm-like glass-coated microwires obtained by Taylor-Ulitovsky technique with nanocrystalline structure consisting of about 20–30 nm BCC α-FeCo and an amorphous precursor in as-prepared samples. We observed a considerable decrease of the average grain size (from about 23 to 11 nm) after annealing. As-prepared and annealed Fe38.5Co38.5B18Mo4Cu1 Hitperm-like glass-coated microwires present rectangular hysteresis loops and fast domain wall propagation. We measured and analyzed the frequency dependence of the switching field dependence and domain wall dynamics in as-prepared and annealed Hitperm-type microwires. Obtained results are discussed in terms of the microstructural relaxation, grains refinement and internal stresses relaxation. An enhancement of the domain wall velocity as well as mobility after annealing has been attributed to the structural relaxation of such grains with positive magnetostriction.

Giant magnetoimpedance effect and domain wall dynamics in Co-rich amorphous microwires

The giant magnetoimpedance (GMI) effect, as well as the magnetic and magneto-optical properties, of Co69.2Fe4.1B11.8Si13.8C1.1 and Fe73.8Cu1Nb3.1B9.1Si13 amorphous microwires is studied. It is observed that the magnetic properties and the GMI effect of the Co-rich microwire can be tuned by heat treatment. A high GMI effect has been observed in as-prepared Co-rich microwires. After appropriate annealing of the Co-rich microwires, fast domain wall propagation and a GMI effect can be simultaneously observed in the same sample, and annealing is seen to affect both the diagonal and off-diagonal GMI components. Using complementary studies of the bulk and surface magnetic properties, an attempt is made to explain the great difference observed in the GMI properties of Co- and Fe-based microwires exhibiting very similar bulk hysteresis loops.

Domain Wall Propagation in Co-Based Glass-Coated Microwires: Effect of Stress Annealing and Tensile Applied Stresses

RECENTLY, domain wall (DW) propagation in magnetic wires has been recognized as one of the important lines of research due to its potential use in magnetic devices [1]–[7]. The DW speed and the possibilities for the DW dynamics manipulation are quite relevant for these applications. Extremely fast DW propagation has been reported for amorphous magnetically bistable microwires with positive magnetostriction constant λs and circular cross section (usually, exceeding 1000 m/s) [3], [4]. On the other hand, ferromagnetic glass-coated microwires have attracted growing attention in the last few years, mostly owing to their outstanding soft magnetic properties (magnetic bistability, enhanced magnetic softness, Giant magnetoimpedance (GMI) effect, and fast DW propagation) [5]–[7]. These microwires have a composite character consisting of a cylindrical metallic nucleus of (1–30 μm) and glass coating (with thickness of 1–20 μm). These microwires can be prepared by the modified Taylor–Ulitvosky technique, which involves simultaneous rapid quenching and drawing of the metallic nucleus inside a glass capillary [6], [7]. Thus, strong stresses are introduced in the metallic nucleus arising from the drawing and quenching, as well as from the different thermal expansion coefficient between the glass sheath and the metallic nucleus [5], [6], [8]–[10]. Therefore, the magnetoelastic anisotropy induced by the internal stresses plays an important role in controlling their magnetic properties [4], [5], [7]–[9]. Fe-rich microwires with positive magnetostriction coefficient, λs , present magnetic bistability related to a large and single axially magnetized inner core. Therefore, one can observe quite fast magnetization switching within the single magnetic domain related with fast DW propagation. In particular, these materials are unique for studying the DW propagation since they can exhibit a very fast DW velocity [2]–[4], [6], [11]. On the other hand, it is well known that the DW dynamics in glasscoated microwires is strongly dependent to external parameters

Tailoring of magnetic properties and GMI effect of Co-rich amorphous microwires by heat treatment

We studied effect of annealing on Giant magnetoimpedance (GMI) effect and magnetic properties of amorphous Fe and Co-rich microwires. High GMI effect has been observed in as-prepared Co-rich microwires. We observed that changing the annealing conditions we can obtain a great variety of properties in Co-rich microwire. High domain wall (DW) velocity and rectangular hysteresis loops we observed in heat treated Co-rich microwires. We observed increasing of the DW velocity under stress and coexistence of the GMI effect and fast DW propagation in the Co-rich microwires annealed at certain conditions. Fe-rich microwires with similar bulk hysteresis loop do not present considerable GMI effect. We assume that the outer domain shall of the annealed Co-rich microwire exhibiting both fast DW propagation and GMI effect has high circumferential magnetic permeability. Observed fast DW propagation in both kind of microwires is related to the fast magnetization switching within the single domain axially magnetized inner core, i.e. related to the remagnetization process of the inner part of the microwire.

Imaging the Surface Domain Structure of Amorphous Glass-Coated Microwires by Bitter Colloid

The fast domain wall dynamics of amorphous glass-coated microwires can be changed drastically by properly selected annealing temperature. Here, the e ect of thermal annealing on the surface domain structure of microwires is examined. Imaging the surface domain structure by Bitter colloid revealed the periodic pattern in each studied sample. Thermal annealing of microwires results in the ve times increase of the domain wall velocity, as compared to the as-cast state. In uence of the surface domain structure on the fast domain wall propagation in microwires is discussed.

Fast Magnetization Switching in Amorphous Microwires

We studied the magnetization switching in magnetically bistable amorphous ferromagnetic microwires. We observed quite fast domain wall propagation along the microwires and a correlation between the magnetoelastic anisotropy, distribution of the local nucleation eld along the length of microwire and the domain wall dynamics. We observed that both DW velocity and the range of elds, limiting single DW dynamics, can be manipulated by internal or applied stresses and by annealing. We also observed that under certain conditions a controllable domain wall (DW) collision can be realized in di erent parts of the wire, and that it is possible to manipulate the DW dynamics in a eld-driven regime.

Magnetic properties and domain wall propagation in FeNiSiB glass-coated microwires

We studied magnetic properties and domain wall propagation in Fe77.5−xNixSi7.5B15 (0 ≤ x ≤ 77.5) microwires considering effect of applied and internal stresses. We observed rectangular hysteresis loops and fast domain wall propagation for the Fe77.5−xNixSi7.5B15 (0 ≤ x ≤ 38.75) microwires. We measured dependences of domain wall velocity on applied magnetic field for the Fe77.5−xNixSi7.5B15 microwires with x ≤ 38.75. In Fe77.5Si7.5B15 and Fe62Ni15.5Si7.5B15 samples, we observed domain wall velocities up to 2.5 km/s. In all studied samples exhibiting fast domain wall propagation, we observed reduction of domain wall velocity under application of tensile stresses.

Manipulation of fast magnetization switching in magnetically bistable microwires through the magnetoelastic anisotropy

IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, SpainWe studied effect of magnetoelastic anisotropy and role of defects on domain wall (DW) dynamics andremagnetization process of magnetically-bistable microwires. We manipulated the magnetoelastic anisotropychanging the ratio between the metallic nucleus diameter and glass coating thickness and applying the tensilestresses. Application of stresses resulted in increase of the switching field and decrease of the DW velocity, v. Therole of defects existing in magnetically bistable microwires is related with nucleation of new reversed domains.Abrupt jumps on v(H) dependences correlate with defects existing in microwires. Annealing allows considerablyincrease DW velocity, enhances the magnetic field range of single DW propagation regime and domain wall mobility.Key words: amorphous microwires, domain wall dynamics, magnetic anisotropy1. IntroductionStudies of domain wall (DW) propagation in thinmagnetic wires prepared by different methods attractedgrowing attention during last few years [1, 2]. Maintechnological interest is related with proposedapplications involving the information storage,magnetic sensors and logics. For aforementionedapplications the DW speed and the ways for the DWdynamics manipulation are essentially relevant.Reported DWs propagation can be driven by themagnetic field as well as by the electric current flowingthrough the sample. The DW velocity is determined bythe magnetic field value as well as by the shape anddimensions of the wires [1, 3-6]. Thus, for amorphousmicrometric wires with circular cross section fastest DWvelocity (exceeding 1000 m/s) have been reported [7,8].Additionally the DW velocity, v, depends on themagnetoelastic anisotropy depending on themagnetostriction constant value as well as on theinternal or applied stress [9]. On the other hand, forcontrolling the DWs dynamics in thin wires (either withrectangular or cylindrical cross-section), fewmechanisms involving the DW injection, creation ofartificial defects and inhomogeneities, controllable DWcollision etc have been reported [9, 10].Studies of glass-coated microwires withferromagnetic nucleus attracted considerable attentionwithin last few years owing to their reduced dimensionsand unusual soft magnetic properties such asspontaneous magnetic bistability, Giantmagnetoimpedance effect and high magneticpermeability. Magnetic bistability is related with largeand single Barkhausen jump observed in amorphousmicrowires with positive magnetostriction constant isparticularly interesting for studies of the DWpropagation within the inner core of microwire [5-7, 11].On the other hand giant magneto-impedance, GMI,effect and extremely soft magnetic properties can beuseful for magnetic sensors applications [12, 13].Abovementioned magnetic bistability observed inamorphous glass-coated microwires with positivemagnetostriction constant is related with fastmagnetization switching of a large single axiallymagnetized domain by fast DW propagation of a singleDW [5-8, 11, 13]. Therefore these microwires are uniquematerial allowing studying the magnetization dynamicsof a single DW in a cylindrical micrometric wire.Appearance of such peculiar domain structureconsisting of a large single axially magnetized domainsurrounded by outer radially magnetized shell isdetermined by the stresses arising during rapidsolidification of composite thin wire [5, 13-17]. Thestrength of these stresses originated from the differencein thermal expansion coefficients of the metal and glassis determined by the volumes of metallic nucleus andglass coating [14-16]. Consequently the magneticsoftness of glass-coated microwires is determined by themagnetoelastic anisotropy originated from thecomposite character being also depending on themetallic nucleus composition and ratio between themetallic nucleus diameter, and total microwirediameter.Consequently fast magnetization switching ofmicrowires is related with the propagation of the singlehead-to head DW along the wire.Recently we reported, that the samplesinhomogeneities, observed through the measurementsof the distribution of the local nucleation fields, H

Manipulation of domain wall dynamics in amorphous microwires through the magnetoelastic anisotropy

We studied the effect of magnetoelastic anisotropy on domain wall (DW) dynamics and remagnetization process of magnetically bistable Fe-Co-rich microwires with metallic nucleus diameters (from 1.4 to 22 μm). We manipulated the magnetoelastic anisotropy applying the tensile stresses and changing the magnetostriction constant and strength of the internal stresses. Microwires of the same composition of metallic nucleus but with different geometries exhibit different magnetic field dependence of DW velocity with different slopes. Application of stresses resulted in decrease of the DW velocity, v, and DW mobility, S. Quite fast DW propagation (v until 2,500 m/s at H about 30 A/m) has been observed in low magnetostrictive magnetically bistable Co56Fe8Ni10Si10B16 microwires. Consequently, we observed certain correlation between the magnetoelastic energy and DW dynamics in microwires: decreasing the magnetoelastic energy, Kme, DW velocity increases.