Magnetostrictive Amorphous Alloys Research Articles

Magnetoelectric effect in a Metglas–langatate ring heterostructure for current sensing

The magnetoelectric (ME) effect was observed and investigated in a planar ring-type heterostructure containing mechanically coupled rings of magnetostrictive amorphous alloy Metglas and a piezoelectric single crystal langatate. The structure was excited by a circumferential ac magnetic field in the presence of a circumferential dc bias magnetic field. Due to the absence of demagnetization and the high acoustic quality factor of the langatate, a high ME field conversion coefficient of α E ≈ 53 V (Oe cm)−1 was obtained at the frequency 221 kHz of the fundamental radial acoustic resonance mode. The structure can be used as a non-contact ac or dc current sensor. The sensitivity of the structure to the ac current was 1.6 V A−1, whereas for the dc current it reached 4.2 V A−1.

Методы увеличения магнитоэлектрического эффекта в композитных структурах: обзор

The article provides a review of various methods that can be used to increase the magnetoelectric (ME) effect in composite structures based on magnetostrictive and piezoelectric materials. It is shown that the use of adhesive technology and gradient structure, as well as thermal and thermomagnetic treatment of a magnetostrictive amorphous alloy of an ME structure make it possible to achieve a significant increase in the ME effect. To date, great efforts have been made to optimize the strain amplitude in the piezoelectric and magnetostrictive phases of multilayer ME materials. The use of various technologies in the manufacture of ME composites makes it possible, for example, to increase the sensitivity of magnetic field sensors for biomedical applications. Also, an increase in the ME effect opens up great prospects for further research.

Magnetic field spectrum analyzer using nonlinear magnetoelectric effect in composite ferromagnet - piezoelectric heterostructure

Industrial machines and mechanisms, household appliances, natural sources and biological objects generate weak magnetic fields with amplitudes of ~10 –12 – 10 –4 T in the frequency band of ~1–10 5 Hz. Analysis of the fields’ characteristics allows to get information about internal processes and performance of these sources in a non-contact way, to carry out medical diagnostics. This makes topical the development of low-frequency magnetic field spectrum analyzers. The paper describes a spectrum analyzer of a new type using nonlinear effect of magnetic field mixing in a composite ferromagnet-piezoelectric heterostructure. The main element of the analyzer is a magnetic field mixer which contains a piezoelectric langatate single-crystal sandwiched between two layers of a magnetostrictive amorphous alloy. With simultaneous action of the measured magnetic field and the excitation magnetic field on the structure and fulfillment of the frequency matching conditions, the structure generates a voltage at the electromechanical resonance frequency. Swept-tuned spectrum analysis of the measured field is carried out by tuning the frequency of the excitation field. A prototype of the analyzer is fabricated and characterized. It operates in the frequency band of 0.1–85 kHz, has a frequency resolution of ~40 Hz, a minimum detectable field of 50 nT, and a dynamic range of 35 dB. Possibilities to improve characteristics of magnetic field spectrum analyzers are discussed. • A new swept-tuned spectrum analyzer of magnetic fields is proposed. • The analyzer uses resonant magnetoelectric effect of magnetic field frequency mixing. • A prototype of the spectrum analyzer is fabricated and characterized.

Hybrid magnetoelectric converter

The article is devoted to the study of a hybrid magnetoelectric voltage converter. The article deals with the magnetoelectric structure of the converter with its design features. The measuring stand with the calculation of the converter parameters is also described and the measurement results are given. In the manufacture of the ME element, materials such as piezoelectric PZT and magnetostrictive amorphous alloy Metglas were used. ME is a layered element, which consists of a PZT plate with electrodes applied to the lateral surfaces and one or more Metglas layers. The Metglas plates are connected to the piezoelectric using an adhesive bond. In experimental studies, the number of Metglas layers varied from one to three. The article discusses the design of the converter and the choice of the most optimal of the ones under study. As a result of the study, the lowest indicators were found for a converter without a core, the more Metglas layers, the better the characteristics of the converter. The ME element at the resonant frequency converts energy much better (the conversion power was about 130 μW) than the design of a conventional converter, and also a hybrid converter based on a series switching circuit gives an even greater gain in energy conversion (the conversion power was about 180 μW).

Suppression of the magnetoelectric hysteresis in a composite langatate-metglas structure

The suppression of the magnetoelectric effect hysteresis in a composite planar structure containing mechanically coupled layers of piezoelectric langatate and magnetostrictive amorphous alloy Metglas was observed and investigated. As the pumping magnetic field with frequency ~84 kHz was increased from 0.6 Oe up to 20 Oe, the coercive fields for the 1st and 3rd voltage harmonics generated by the structure were decreased from ~0.7 Oe up to zero. The suppression of the magnetoelectric hysteresis will allow increasing of absolute accuracy of the magnetoelectric magnetic field sensors by ~2 orders of magnitude.

Voltage-Controlled Uniaxial Magnetic Anisotropy in Soft Magnetostrictive Ferromagnetic Thin Films

A push-pull type ferromagnetic (FM)/ferroelectric (FE) composite was realized with depositing soft magnetostrictive amorphous (Fe65Co35)80B20 alloy on top of the microfiber lead zirconate titanate commercial composite. The piezoelectric and magnetic hysteresis loops of the FM/FE composite were measured with different electric field polarization. We report a remarkable large converse magnetoelectric effect at room temperature including reversible tuning of the in-plane uniaxial anisotropy. The experimental results were analyzed based on strain-induced magnetization change theory. For this purpose, the applied stress to FM resulting from the piezoelectric strain of FE and the saturation magnetostriction of FM were evaluated. The results indicate a high magnetostriction constant value of 110 ppm and moderate useful applied stress of ± 50 MPa. We conclude that the combination of soft magnetostrictive FM with push-pull type piezoelectric FE is suitable for ultralow power electric field writable or tunable electronic devices.

Magneto‐elasticity in amorphous ferromagnets: Basic principles and applications

AbstractFerromagnetic metallic glasses (FMG) show a very special combination of magnetic, elastic, and magnetostrictive properties that have rocketed their most extended technological applications, mainly in the field of sensors and surveillance labels. The amorphous structure results in the cancellation of the magnetic anisotropy as a result of the averaging out of the atomic scale local anisotropy in a region of the order of the exchange correlation length. Magnetostriction, however, does not cancel out, and values similar to the corresponding crystalline alloys are displayed by the amorphous ones. The absolute values of magnetostriction are not very high, but the extremely magnetic softness of the alloys does balance the competition between stress and magnetic field. In particular, the magnetoelastic coupling coefficient can reach values as high as 0.98, the highest in any known material. Magnetoelasticity, defined as the magnetization change caused by stress, reaches outstanding values in FMGs and a number of applications do use such properties for sensing applications. We can briefly review some of them, either based on static or magnetoelastic wave resonance operation. The most widely extended application is their use as magnetoelastic resonant elements in electronic surveillance labels. New applications of FMGs are under development. Hybrid magnetoelectric (magnetostrictive/piezoelectric) materials have been devised, using highly magnetostrictive amorphous alloys working at resonance. Possible applications of such new materials are briefly discussed.

Electronic Article Surveillance Marker

A fabrication process produces markers for a magnetomechanical electronic article surveillance system. The marker includes a magnetomechanical element comprising one or more resonator strips of magnetostrictive amorphous metal alloy; a housing having a cavity sized and shaped to accommodate the resonator strips for free mechanical vibration therewithin; and a bias magnet to magnetically bias the magnetomechanical element. The process employs adaptive control of the cut length of the resonator strips, correction of the length being based on the deviation of the actual marker resonant frequency from a preselected, target marker frequency. Use of adaptive, feedback control advantageously results in a much tighter distribution of actual resonant frequencies. Also provided is a web-fed press for continuously producing such markers with adaptive control of the resonator strip length.

Rf-Mössbauer study of the magnetic properties of nanocrystalline FeNiZrB and FeNiCoZrB alloys

Magnetic properties of amorphous and nanocrystalline Fe31Ni50Zr7B12 and Fe41Ni40−xCoxZr7B12 (x=10,20) alloys are studied by an unconventional “rf-Mössbauer” technique. The introduction of Co atoms into FeNiZrB amorphous and nanocrystalline alloys leads to a large increase of anisotropy field that limits the rf-collapse effect. The rf-Mössbauer measurements are very useful for the estimation of magnetic anisotropy field. The rf sidebands vanish when the nanocrystalline structure is formed. The rf-induced crystallization effect observed in Co-containing alloys is particularly strong in magnetostrictive amorphous alloys and in nanocrystalline alloys containing significant fraction of amorphous matrix. This effect does not occur in Co-free alloy.

The cryogenic treatment effect on the magneto-impedance properties of the Co- and Fe-based amorphous ribbons

The influence of the cryogenic treatment and following annealing on the magneto-impedance properties in Co-based (Co 66 Fe 4 B 15 Si 15 ) with near-zero magnetostriction and Fe-based (Fe 60.8 Co 20.2 Si 5 B 14 ) with positive magnetostriction amorphous alloys were investigated. The magneto-impedance measurements were made in frequency range from 100 kHz up to 10 MHz. It was found that the cryogenic treatment increases the magneto-impedance effect up to 60-70%. The Co-based alloys with cryogenic treatment kept larger value of the magneto-impedance ratio after annealing.

Peculiarities of the Low Magnetostrictive Amorphous Ribbons Crystallization Under Laser Heating

The crystallization of the low magnetostrictive amorphous metallic alloy Co 68 Fe 4 Cr 4 Si 13 B 11 obtained by melt-spinning after bulk annealing (BA) and surface laser heating (LH) has been investigated by X-ray powder diffraction method. As shown, both at volume and laser heating the first phase to crystallize was cobalt. Increase in BA temperature led to the formation and decomposition of a great number of metastable phases. Stable phases Co and (Co,Si) 2 B appeared as final products of crystallization. The number of simultaneously coexisting crystalline phases was smaller after LH. The final products of crystallization under LH in the most permissible regimes (those not leading to the sample decay) were the phases Co, (Co,Si) 3 B and (Co,Si) 2 B (under pulse LH) and Co, (Co,Si)B and (Co,Si) 2 B (under continuous CO 2 LH). A sandwich structure was observed in the cross section of the ribbon after some regimes of LH. The ribbon was crystalline at the side of the treated surface and amorphous at the side of the opposite surface. X-ray analysis revealed that the high rates of laser heating and cooling lead to a change in crystallization reaction: from the primary crystallization observed at BA to the eutectic crystallization at LH.

Development of a pinned wall sensor using cobalt-rich, near-zero magnetostrictive amorphous alloys

A novel type of a harmonic sensor that is based on the concept of the domain wall pinning is described. Two-step annealing of the cobalt-rich amorphous precursors gives rise to the unique signature, which is attributable to the hysteresis loop with a step change in flux. The first annealing under a magnetic field causes a field-induced uniaxial anisotropy in M-H loop whose origin is believed to be due to structural inhomogeneities produced by internal segregation of oxygen atoms on cobalt {111} lattice planes. Subsequent annealing without magnetic field gives rise to the pinned wall stepped hysteresis characteristic, which is indicative of the useful markers. During annealing, it is observed that the surface and bulk of the amorphous material undergo substantial oxidation and crystallization. Consequently, microstructural features affect tag performance significantly. Those features, including (1) crystal structure of the cobalt layer (fcc or hcp), (2) oxygen faulting in cobalt layer, (3) surface oxide, and (4) magnetic state of the cobalt layer, are discussed. In addition, a surface wall pinning model is suggested since we are convinced that wall pinning is most effectively achieved at the interface between the amorphous and its semihard cobalt layer. It is also observed that there is a good correlation between domain wall pinning field and thickness of crystalline Co layer.

Hydrogen induced anisotropy in magnetic amorphous ribbons

A study about induced anisotropy by hydrogen charging has been performed in both, positive and negative magnetostrictive amorphous alloys. A strong perpendicular to surface anisotropy at the sample surface in every hydrogenated sample has been observed from Bitter pattern and from hysteresis loops obtained by magnetooptical Kerr effect. This perpendicular anisotropy is only in the volume fraction near to sample surface, as it is inferred from hysteresis loops and magnetization curves measured by induction. A model assuming that the large perpendicular induced anisotropy is due to the mechanical stresses produced by the change of volume of the hydrogenated zones has been developed. From this model, by fitting experimental results, anisotropy energy, internal stresses, and hydrogen charged volume have been calculated.

Complex permeability after-effects in an annealed Co-based amorphous alloy

We have investigated the magnetic after-effects (MAEs) of the real and imaginary parts of the ac inverse permeability r [r(t) ≡ 1/μ = r1(t) + jr2(t)]. For a near-zero magnetostrictive CoFeCrSiB amorphous alloy, it was found that r1(t) after demagnetization increases, whereas r2(t) mostly decreases. The activation energy spectra which control the MAE1 and MAE2 of r1(t) and r2(t), respectively, show different distributions p1(Q) and p2(Q) in the range 0.72–1.1 eV, with maxima at 0.78 eV (τ0 = 3.6 × 10−14 s).

A magnetoelastic study of a transverse creep-induced magnetic anisotropy in an FeNb-based amorphous alloy

The hard ribbon axis anisotropy induced in the magnetostrictive amorphous alloy Fe 74.7Nb 3Si 12.8B 9.5 by stress annealing at temperatures 633–693 K and under tensile stresses up to 204 MPa has been studied by several experimental methods (measurement of dc hysteresis loops, field dependence of engineering magnetostriction λ e and Young's modulus E, and domain structure observations). The experimental data are discussed in terms of the phenomenological model developed earlier by Squire. The most significant improvement in the magnetoelastic response was found for the highest annealing temperature T a = 693 K. The maximum ΔE effect (27%) observed is much lower than the maximum estimated theoretical value (87%). The λ e and domain studies suggest that this difference is most probably due to the dispersion of easy axes and/or anisotropy values. Even though the phenomenological model does not take into account local variations in the anisotropy, it gives a reasonable quantitative description of a slightly perturbed hard ribbon axis case.

The relationship between microstructure and magnetoelastic response in the magneto strictive amorphous alloy Co 47.4Fe 31.6Si 2B 19 after magnetic field annealing

Activation of the magnetostrictive sensors is achieved by magnetization of the ferromagnetic biasing element. This bias field causes the magneto strictive element to operate near the so-called “knee” of its M-H curve. However, magnetic biasing element complicates the mechanical design and adds cost to the marker structure. It is, therefore, of primary concern to provide a magnetomechanical marker which avoids the need to use a separate biasing element. In order to make a “self-biased” sensor, two-step magnetic annealing of the magnetostrictive amorphous alloy with Co 47.4Fe 31.6Si 2B 19 composition was devised. After annealing, the surface was fully crystallized and formation of α-iron crystallites was observed in the bulk of the amorphous ribbon. With this surface layer and the low density of α-iron particles in the bulk of the ribbon, a reasonably long ring-down time was achieved. The low acoustic and eddy current loss appear to be attributable to the low density of α-iron particles in the bulk of the ribbon. It appears that this crystallized surface layer can replace a bias magnet since the semi-hard surface layer fixes the magnetic domain configuration which is necessary for the operation of the sensor material. It was also found that microstructural changes during magnetic field annealing appear to be critical to the tag performance.

Experimental evidence of slow dynamics in amorphous metal using fiber-optic interferometry

New results on the study of slow dynamics in ferromagnetic amorphous alloys are presented. Experimental evidence has been obtained of low-frequency relaxation phenomena in highly magnetostrictive amorphous alloys submitted to various anneal treatments. Dynamics of the amplitude and phase of intrinsic magnetic noise in the metallic glass Metglas 2605S-2 have been measured with a fiber-optic interferometer.

Induced transverse magnetic anisotropy in Co-based amorphous alloys with different values of the saturation induction

The magnetic properties and domain structure of three near-zero magnetostrictive amorphous alloys: Co 71.5Fe 2.5Mn 2Mo 1B 14Si 9, Co 76Fe 2Mn 4B 12Si 6 and Co 68Fe 4Mo 1.5B 13Si 13 (at%), with different values of the saturation induction, were investigated as functions of two-step magnetic annealing parameters: preannealing time t a and strength of transverse magnetic field H T applied during cooling.

Creep-induced magnetic anisotropy in Co-57Fe-Ni-Si-B amorphous alloys

The effect of creep annealing on the57Fe enriched Co-rich low magnetostriction amorphous alloys will be reported. Contrary to the Fe-B-base alloys, after creep annealing of the57Fe5Co57Ni10Si11B17 the ribbon axis becomes the hard direction. Both Mossbauer spectroscopy and direct magnetic domain observations by SEM confirmed an enhanced volume with magnetization oriented in transversal and normal directions to the ribbon axis. Relaxation of the creep-induced state at a temperature slightly below that of the creep annealing leads to the enhancement of the fraction of domains magnetized in the longitudinal direction.

On the theoretical understanding of nanocrystalline soft magnetic materials

Nanocrystalline structures offer a new opportunity for tailoring soft magnetic materials. The most prominent examples are devitrified glassy FeCuNbSiB alloys, which exhibit a homogeneous ultrafine grain structure of bcc FeSi, with grain sizes of typically 10 to 15 nm and random texture. Due to the small grain size, the local magnetocrystalline anisotropy is randomly averaged out by exchange interactions so that there is only a small anisotropy net effect on the magnetization process. Moreover, the structural phases present lead to low or vanishing saturation magnetostriction. Both the suppressed magnetocrystalline anisotropy and the low magnetostriction provide the basis for the superior soft magnetic properties comparable to those of Permalloys or near-zero magnetostrictive Co-base amorphous alloys, but at a higher saturation induction.