Amorphous Soft Magnetic Materials Research Articles

Fabrication and magnetic properties of Cu50(Fe69Si10B16C5)50 thin microwires

In this work, we study the granular samples of mixed Cu50(Fe69Si10B16C5)50 composition where half of alloy composition is commonly used amorphous soft magnetic material and the other half-Cu. Glass covered Cu50(Fe69Si10B16C5)50 microwires were produced and their magnetic properties were studied. The evolution of the structure after the annealing was observed using X-ray diffraction with Cu Kα radiation. The as-prepared Cu50(Fe69Si10B16C5)50 microwires present a relatively low coercivity of about 5 Oe and exhibit non-regular hysteresis loop typical behavior for two-phases systems. Annealing resulted in magnetic hardening of the samples with coercivity of about 50 Oe. The variation of the coercivity and remanent magnetization with the temperature at 5–300K were obtained from those curves. Temperature dependence of magnetization at 5–300K exhibits significant difference between field-cooled and zero-field cooled behaviour. Observed dependences interpreted in terms of two-phase structure of as-prepared samples and evolution of the structure under annealing.

Soft magnetic alloys with amorphous and ultra-fine grain structure upon loading with hydrogen

Hydrogenation of amorphous and nanocrystalline iron-rich soft magnetic materials reveals markedly different thermomagnetic behaviors that can be interpreted in terms of microstructure transformations.

Universal control and measuring system for modern classic and amorphous magnetic materials single/on-line strip testers

A new universal control and measuring system for classic and amorphous soft magnetic materials single/on-line strip testing has been developed at the Czech Technical University in Prague. The measuring system allows to measure magnetization characteristic and specific power losses of different tested materials (strips) at AC magnetization of arbitrary magnetic flux density waveform at wide range of frequencies 20 Hz–20 kHz. The measuring system can be used for both single strip testing in laboratories and on-line strip testing during the production process. The measuring system is controlled by two-stage master-slave control system consisting of the external PC (master) completed by three special A/D measuring plug-in boards, and local executing control unit (slave) with one-chip microprocessor 8051, connected with PC by the RS232 serial line. The “user friendly” powerful control software implemented on the PC and the effective program code for the microprocessor give possibility for full automatic measurement with high measuring power and high measuring accuracy.

Fe-based bulk amorphous soft magnetic materials

Fe-based bulk amorphous materials have no crystal anisotropy. This is why they are good candidates for the application as soft magnetic materials, although conventional soft magnetic alloys have a higher saturation magnetization than the amorphous alloys. An Fe 65.5Cr 4Mo 4Ga 4P 12C 5B 5.5 alloy shows, together with excellent soft magnetic behaviour, a very high mechanical strength and a high resistance against corrosion which may be important for application as magnetic parts in valves, clutches, or relays. Fe 77Al 2.14Ga 0.86P 8.4C 5B 4Si 2 bulk amorphous materials were prepared by the powder-metallurgical technology. This technological route allows to prepare samples of larger dimensions. Furthermore, active powders, e.g. high magnetostrictive Fe 2Sm-powder, may be added to the powder. Thus, composites with high magnetostrictive response and high mechanical strength may be prepared profiting from the low processing temperature.

Magnetic properties and crystallization behaviour of Fe 28.75Co 28.75Ni 17.5X 8B 17 (X=Si, Ge) metallic glasses

The development of Fe- and Co-based amorphous soft magnetic materials with low critical cooling rate for glass formation has become an important topic both for fundamental and technological reasons. We have synthesized new alloys with composition Fe 28.75Co 28.75Ni 17.5X 8B 17 (X=Si or Ge) and we have studied the evolution of their magnetic and crystallographic properties when heated from room temperature to 900°C. The techniques used to measure their evolution are in situ powder neutron diffraction and Faraday magnetic torque. We observe a phase stability competition between the SC (α 2), BCC (α) or CCP (γ) forms.

Magnetic properties and crystallization behavior of Fe28.75Co28.75Ni17.5X8B17 (X=Si, Ge) metallic glasses

Abstract The development of Fe- and Co- based amorphous soft magnetic materials with low critical cooling rate for glass formation with a wide supercooled liquid region before crystallization has become an important topic for fundamental as technological reasons. We have synthesized new alloys with composition Fe 28.75 Co 28.75 Ni 17.5 X 8 B 17 (X=Si or Ge) and we have studied the evolution of their magnetic and crystallographic properties when heated from room temperature to 900°C. The techniques used to measure their evolution are in situ powder neutron diffraction and Faraday magnetic torque. As synthesized, the alloys are vitreous with a supercooled liquid region of 48°C for the Si and Ge alloys, they are ferromagnetic with ordering temperatures of 420°C and 430°C for the Si and Ge alloys, respectively. There is a phase stability competition between the cs, BCC (α) or ccp (γ) forms as a function of the substitution scheme of the 3d transition metals (Fe, Co, Ni).

Dipolar magnetic interactions among magnetic microwires

This paper presents a brief review of experiments and simulations on dipole–dipole interacting magnetic microwires that form a linear chain. In particular, recent studies on (a) amorphous Fe 77.5Si 7.5B 15 and (b) granular Cu 45Ni 25Co 29Mn 1 microwires are discussed. Hysteresis loops were performed at room temperature for an array of N microwires ( N=1–5 for (a) and N=1–100 for (b)) and compared with Monte Carlo simulations. In the case of amorphous soft magnetic materials (a), clear steps and plateaux on the demagnetization are visible, each step corresponding to the magnetization reversal of an individual wire. In the case of CuNiCoMn microwires (b), that exhibit a granular structure and a nearly superparamagnetic behavior when isolated, it was found that the coercivity abruptly changes from 20 to 700 Oe for N around 10. Novel Monte Carlo simulations are presented, providing useful insights about the effect of long-range interactions that account for the interesting observed magnetic behaviors.

Bulk Glassy Co<SUB>43</SUB>Fe<SUB>20</SUB>Ta<SUB>5.5</SUB>B<SUB>31.5</SUB> Alloy with High Glass-Forming Ability and Good Soft Magnetic Properties

A new Co-based bulk glassy alloy Co43Fe20Ta5.5B31.5 exhibiting a large supercooled liquid region before crystallization and good soft magnetic properties was synthesized by the copper mold casting method. The glass transition temperature (Tg) is 910 K and the supercooled liquid region (ΔTx) reaches 70 K . The high thermal stability of the supercooled liquid enabled us to produce bulk glassy alloys with diameters up to 2 mm. These bulk glassy alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.5 T, very low coercivity of 0.9 A/m and very high permeability of 40000 at 1 kHz. It is noticed that the diameter of 2 mm is the largest value for Co-based bulk glassy alloys reported up to now. The success of forming the large-scale size Co-based bulk glassy alloy with high thermal stability of supercooled liquid and good soft magnetic properties is encouraging for future uses of bulk amorphous soft magnetic materials.

Thermal Stability and Soft Magnetic Properties of Co–Fe–M–B (M=Nb, Zr) Amorphous Alloys with Large Supercooled Liquid Region

A ferromagnetic amorphous phase with a large supercooled liquid region prior to crystallization and good soft magnetic properties was formed in melt-spun Co 40 Fe 22 Nb 8-x Zr x B 30 (x = 0, 2, 4, 6, and 8 at %) alloys. The glass transition temperature (T g ) increases monotonously with increasing Zr content, The crystallization temperature (T x ) also increases by the dissolution of Zr up to 2% and then decreases with further increasing Zr content. The increases is more significant for T x , resulting in a maximum ΔT x (=T x - T g ) of 98 K at 2% Zr. The Co-based amorphous alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.41 T-0.42 T, low saturated magnetostriction of 2.4 × 10 -6 -2.9 × 10 -6 , low coercivity of 1.2-2.0 A/m, and high permeability of 29000-33000 at 1 kHz over the whole Zr content range. In addition, the cylindrical Co 40 Fe 22 Nb 6 Zr 2 B 30 glassy alloy with a diameter of 1.0 mm was prepared by the copper mold casting method. With increasing the cylindrical diameter up to 1.5 mm, the structure changes to coexistent amorphous, Co 21 Nb 2 B 6 , Co 3 ZrB 2 and Co 2 B phases. It is noticed that the maximum thickness for glass formation is about 6 times larger than that for Co-based amorphous alloys reported up to date. The success of forming Co-based bulk amorphous alloys with high stability of supercooled liquid and good soft magnetic properties is encouraging further development of bulk amorphous soft magnetic materials.

Giant magnetoimpedance in crystalline Mumetal

We studied giant magnetoimpedance (GMI) effect in commercial crystalline Mumetal, with the emphasis to sample thickness dependence and annealing effects. By using appropriate heat treatment one can achieve GMI ratios as high as 310%, and field sensitivity of about 20%/Oe, which is comparable to the best GMI characteristics obtained for amorphous and nanocrystalline soft magnetic materials.

On the effectiveness of magnetotactic bacteria for visualizations of magnetic domains

In an earlier paper we demonstrated that magnetotactic bacteria (MB) can be applied for nondestructive visualizations of domain structures in soft magnetic materials. In comparison with colloid techniques, this method shows a much higher sensitivity due to a different contrast mechanism. The present paper discusses limits of practical application of this technique regarding the possible resolution of narrow domains and supplementary domains respectively. Due to Brownian motion of the cells on SiFe a visualization is in principle restricted to domains of width d > 60 μm as well as to main domains. Experiments and an analysis of the contrast mechanism in connection with results of computer simulations of the spatio-temporal MB distribution indicate that stray fields of amorphous soft magnetic materials are too weak to allow a resolution of their narrow surface structure by means of motile MB. However, it can be visualized by means of MB with lost motility.

Depth selective analysis of phases and spin textures in amorphous, nanocrystalline and crystalline ribbons treated with an excimer laser

Iron-based amorphous alloys have attracted technological and scientific interest due to their soft magnetic properties. Recently it was found that amorphous alloys like Fe73.5Cu1Nb3Si13.5B9 undergo a transition to the nanocrystalline state after proper annealing, thus exhibiting excellent magnetic properties. Laser surface treatment of amorphous soft magnetic materials is known to have a strong influence on their spin texture. Laser treatment of crystalline alloys can induce changes in their phase structure, as for example the amorphization of surface layers. In this study, the authors report on the reaction of both Fe- and Co-based amorphous alloys as well as nanocrystalline and crystalline Fe73.5Cu1Nb3Si13.5B9 on excimer laser treatment. Simultaneous triple radiation Mossbauer spectroscopy (STRMS) is a powerful tool for the study of these phenomena. In order to estimate the depths of origin of the spectral information, simple analytical expressions for the depth profiles of the involved techniques are calculated.

Investigations of Bloch wall mobility in crystalline and amorphous soft magnetic material

For interpretation of iron losses in crystalline soft magnetic materials various models of domain wall motion have been applied in the past. This paper presents experimental studies of Bloch wall mobility in grain-oriented 3% SiFe and amorphous material. Measurements were performed by means of a video-camera equipped conventional Kerr-effect system and a newly developed laser scanning Kerr-effect sensor, respectively. Effects of wall pinning and symmetry of wall motion are discussed.

Main domains and surface domains in amorphous soft magnetic materials

Contrary to domain structures typical for extremely anisotropic crystalline materials, amorphous materials show a basically different set-up. At least in the case of pre-annealed samples, the inner structure of 180° bulk domains of some millimetres width is accompanied by irregular surface maze domain patterns with typical width of some 10 μm. The paper presents a comparison of both inner and surface domain structures of Fe-, Co- and FeNi-based types of amorphous ribbons received from the magnetotactic bacteria method, the zero-field colloid technique and the destruction-free laser scanning procedure.

Amorphous soft magnetic materials and their application

This paper reports on the amorphous soft magnetic alloys produced in Russia. There are about 20 sorts of alloys - Fe and Co-based, their magnetic properties are described, data on the application of amorphous alloys in various equipment are cited.

Novel Solid State Powder Processing for Amorphous Soft Magnetic Materials

Novel Solid State Powder Processing for Amorphous Soft Magnetic Materials

Amorphous soft magnetic materials: magnetostriction and induced anisotropies

The following characteristics of the magnetic behavior of Co based amorphous ferromagnets are reviewed: 1) macroscopic anisotropy as a result of random orientation of local easy axes; 2) macroscopic magnetostriction, its thermal, compositional, annealing conditions, and stress dependence, and 3) stress and field induced anisotropies. Recent experiments carried out by using EXAFS on the series (Co 1- x Fe x ) 75Si 15B 10 have shown that some type of short range order appears at the neighborhood of Fe atoms in the low Fe content region. That suggests that in the range from x=0 to x=0.5 probably two amorphous phases coexist. The influence of this structure on the magnetostriction and anisotropy is discussed.

Problems of loss separation for crystalline and consolidated amorphous soft magnetic materials

Losses were measured as a function of magnetization frequency f/sub d/ for two advanced soft magnetic alloys: laser-scribed 0.23-mm HI-B steel ZDKH (designated HB) and consolidated amorphous Powercore (designated PC). Although domain observations on HB yielded distinct domain refinements due to the laser treatment, anomalous losses W/sub a/ still proved to be higher than the classical ones. A further refinement resulted from increasing f/sub d/. Thus, anomalous eddy current losses were reduced while hysteresis losses were increased. As a consequence, it is suggested to separate W/sub a/ into an eddy current component and a hysteresis component, which arises in addition to the classical hysteresis loss. With increasing f/sub d/, especially wide domains were refined. Results of loss measurements performed at high f after demagnetization with low f/sub d/ indicated similar bar-type domain structures in HB and PC, the domain widths of the latter exceeding those of HB, however, by one order of magnitude. A Kerr-effect scanning technique confirmed the existence of an inner bar-type domain structure with domain widths of some millimeters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Domain walls and a wall-pinning effect in amorphous magnetic materials

The wall thickness and the initial susceptibility as well as the coercivity of amorphous magnetic material were calculated on a simple theory concerned with the micro-structure-magnetic anisotropies in it. It is indicated that for amorphous materials the domain patterns observed by Bitter method can be incomplete. It is pointed out that the complication and irregularity of domain configurations and the inhomogeneity of anisotropies in as-prepared amorphous materials are two important reasons for their initial susceptibility to be rather low. It is expected that some of amorphous magnetic materials do not have a clear Hopkinson phenomenon. It is shown that the wall-pinning effect by the gradient of microstructure-magnetic anisotropies is a main mechanism forming the coercivity of amorphous soft-magnetic material, the effects of thermal treatments on the technical magnetic properties of amorphous material are distinct. All the results presented show agreement with experimental data.

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