Search Results (18)

Fe-based amorphous and nanocrystalline alloys, such as FINEMET and its improved variants, are highly valued as green energy-saving materials due to their unique magnetic properties, including high permeability, low coercivity, and near-zero saturation magnetostriction. These characteristics have enabled their extensive use in power electronics and information technology. However, the full potential of these alloys remains unfulfilled due to insufficient understanding of their stress sensitivity. This study focuses on the development history, heat treatment, annealing processes, chemical composition, and underlying mechanisms of Fe-based amorphous and nanocrystalline alloys, aiming to provide insights into stress-induced magnetic anisotropy and guide the development of greener and more efficient soft magnetic materials. Full article

This study investigates the effects of multi-transition metals on the soft magnetic properties of Fe_73.5−xB₉Si₁₄Cu₁Nb₂.₅M_x (M = Nb, Mo, and W) nanocrystalline soft magnetic alloys. Nanocrystalline soft magnetic materials are utilized in electronic components on the basis of their permeability and low core loss. In conventional alloys such as FINEMET, Nb inhibits nanocrystal growth and promotes amorphous formation. In this research, Mo and W were used as additional transition metals to control the size of nanocrystals and explore the potential for enhancing soft magnetic properties. We confirmed that the addition of Mo and W reduced the nanocrystal size, and the activation energy for nanocrystal formation and growth showed significant benefits for nanocrystalline alloys. Consequently, the soft magnetic properties of the alloys containing Mo and W exhibited higher permeability and lower coercivity. These results suggest that multi-transition metals are effective in improving soft magnetic properties by inhibiting nanocrystal formation and growth. Full article

The choice of materials for cores of electrotechnical devices is currently related to energy saving and global warming problems. Nanocrystalline alloys are emerging as materials for cores in these devices in addition to amorphous materials already commonly used due to their better magnetic properties at high operating frequencies. The thermal stability of the magnetic properties of cores is also an important criterion. Keeping these criteria in mind, a study of microstructure and magnetic properties was carried out in this work, and FeCoNbBCu-type material was selected for use as the core of a choke operating in a DC/DC converter in interleaved topology. On the basis of the conducted studies, it was found that good magnetic properties and the best thermal stability were shown by Fe₅₈Co₂₅Nb₃B₁₃Cu₁ alloy. Using RALE software, the technical parameters of the choke core were determined and compared with the same parameters for a choke core made of FINEMET-type alloy. Full article

In this paper, a comparative investigation of the magnetic behavior and its stress dependence in the case of FINEMET glass-coated, glass-removed, and cold-drawn microwires at low and high frequencies, respectively, is presented. The experimental results show major differences between their magnetic properties depending on the preparation method and microwire diameter. The evolution of the magnetic permeability, coercivity, and magnetoimpedance responses with the applied tensile force was investigated and analyzed in correlation with the stresses induced during preparation, their relief following annealing, and the annealing-induced structural transformations. The coercivity dependence on applied force was found to show the highest sensitivity in the glass-removed microwires, while the magnetic permeability and magnetoimpedance sensitivity to force were found to be higher in the cold-drawn samples. The results of this comparative study will enable an enhanced material selection process for various applications in miniaturized magnetic and stress sensors with increased sensitivity. Full article

The absorption of waves of the centimeter and millimeter wavebands in composites with Finemet alloy particles and carbon nanotubes has been studied. It has been established that ferromagnetic resonance and antiresonance are observed in such composites. A method is proposed for calculating the effective dynamic magnetic permeability of a composite containing both a random distribution of ferromagnetic particles and a part of the particles oriented in the same way. In the approximation of effective parameters, the dependences of the transmission and reflection coefficients of microwaves are calculated. It is shown that the theoretical calculation confirms the existence of resonant features of these dependences caused by ferromagnetic resonance and antiresonance. The theory based on the introduction of effective parameters satisfactorily describes the course of the field dependence of the coefficients and the presence of resonance features in these dependences. The frequency dependence of the complex permittivity of the composite is determined. The dependence of the complex magnetic permeability on the magnetic field for millimeter-wave frequencies is calculated. Full article

The present review describes our long experience in the application of Mössbauer spectroscopy with a high velocity resolution (a high discretization of the velocity reference signal) in the studies of various nanosized and nanostructured iron-containing materials. The results reviewed discuss investigations of: (I) nanosized iron cores in: (i) extracted ferritin, (ii) ferritin in liver and spleen tissues in normal and pathological cases, (iii) ferritin in bacteria, (iv) pharmaceutical ferritin analogues; (II) nanoparticles developed for magnetic fluids for medical purposes; (III) nanoparticles and nanostructured FINEMET alloys developed for technical purposes. The results obtained demonstrate that the high velocity resolution Mössbauer spectroscopy permits to excavate more information and to extract more spectral components in the complex Mössbauer spectra with overlapped components, in comparison with those obtained by using conventional Mössbauer spectroscopy. This review also shows the advances of Mössbauer spectroscopy with a high velocity resolution in the study of various iron-based nanosized and nanostructured materials since 2005. Full article

⁵⁷Fe transmission and conversion electron Mössbauer spectroscopy as well as XRD were used to study the effect of swift heavy ion irradiation on stress-annealed FINEMET samples with a composition of Fe_73.5Si_13.5Nb₃B₉Cu₁. The XRD of the samples indicated changes neither in the crystal structure nor in the texture of irradiated ribbons as compared to those of non-irradiated ones. However, changes in the magnetic anisotropy both in the bulk as well as at the surface of the FINEMET alloy ribbons irradiated by 160 MeV ¹³²Xe ions with a fluence of 10¹³ ion cm⁻² were revealed via the decrease in relative areas of the second and fifth lines of the magnetic sextets in the corresponding Mössbauer spectra. The irradiation-induced change in the magnetic anisotropy in the bulk was found to be similar or somewhat higher than that at the surface. The results are discussed in terms of the defects produced by irradiation and corresponding changes in the orientation of spins depending on the direction of the stress generated around these defects. Full article

In this experiment, the rare earth Gd element was added to Finemet alloy to observe the microstructure and soft magnetic properties. The experimental results showed that the samples with the addition of 0.5% Gd and 1.0% Gd can be quenched and cast normally, and the M_S of Fe₇₃Cu₁Nb₃Si_13.5B₉Gd_0.5 alloy was 10.41% higher than that of Finemet. After annealing, crystal grains of about 10 nm were formed. The μ_i and μ_m values of Fe₇₃Cu₁Nb₃Si_13.5B₉Gd_0.5 alloy were 25.51% and 22.23% higher, respectively, and the coercivity H_C was reduced by 12.19% compared to Finemet. At 1 kHz, the μ_e value of Fe₇₃Cu₁Nb₃Si_13.5B₉Gd_0.5 alloy at room temperature was 14.57% higher than that of Finemet, while the μ_e reached 162.34 k and 142.42 k at 90 °C and 150 °C (24% and 29.51% higher, respectively). The Fe_72.5Cu₁Nb₃Si_13.5B₉Gd_1.0 alloy had the best performance at 100 kHz, with higher μ_e values than Finemet across the ambient temperature range of 30 °C to 150 °C. After tension annealing, the μ_e values of Fe_72.5Cu₁Nb₃Si_13.5B₉Gd_1.0 alloy were 20–30% higher than those of Finemet. Full article

Soft magnetic materials are at the core of electromagnetic devices. Planar transformers are essential pieces of equipment working at high frequency. Usually, their magnetic core is made of various types of ferrites or iron-based alloys. An upcoming alternative might be the replacement the ferrites with FINEMET-type alloys, of nominal composition of Fe_73.5Si_13.5B₉Cu₃Nb₁ (at. %). FINEMET is a nanocrystalline material exhibiting excellent magnetic properties at high frequencies, a soft magnetic alloy that has been in the focus of interest in the last years thanks to its high saturation magnetization, high permeability, and low core loss. Here, we present and discuss the measured and modelled properties of this material. Owing to the limits of the experimental set-up, an estimate of the total magnetic losses within this magnetic material is made, for values greater than the measurement limits of the magnetic flux density and frequency, with reasonable results for potential applications of FINMET-type alloys and thin films in high frequency planar transformer cores. Full article

Propagation of microwaves is studied in a composite material containing flakes of Fe-Si-Nb-Cu-B alloy placed into an epoxyamine matrix. The theory is worked out, which permits to calculate the coefficients of the dynamic magnetic permeability tensor and the effective magnetic permeability of the transversely magnetized composite. The measurements of magnetic field dependences of the transmission and reflection coefficients were carried out at frequencies from 12 to 38 GHz. Comparison between calculated and measured coefficients were conducted, which show that the calculation reproduces all main features of the resonance variations caused by ferromagnetic resonance and antiresonance. The dissipation of microwave power was calculated and measured. It is shown that the penetration depth of the electromagnetic field increases under antiresonance condition and decreases under resonance. Full article

The microwave properties of a composite material containing flakes of finemet-type nanocrystalline alloy placed in the epoxy matrix have been investigated. Two compositions have been studied: with 15% and 30% flakes. Frequency dependences of transmission and reflection coefficients are measured in the frequency range from 12 to 38 GHz. The dielectric permittivity and magnetic permeability are obtained, and the microwave losses are calculated. The dependences of transmission and reflection coefficients have been drawn as functions of wave frequency and thickness of the composite material, taking into account the frequency dependences of permittivity and permeability. The regions of maximal and minimal microwave absorption have been defined. The influence of wave interference on the frequency dependence of microwave absorption is studied. Full article

To increase the saturation magnetization (M_s) of commercially available soft magnetic Finemet alloys to the level comparable to that of Si-steel and Fe-based nanocrystalline alloys such as Nanoperm, Nanomet, the B or Si content in combination with annealing heat treatment was tailored. The ribbons of Fe_95−xSi₁B_xNb₃Cu₁ (x = 11, 12, 13) and Fe_87−xSi_xB₉Nb₃Cu₁ (x = 6, 8, 10) were prepared by melt-spinning and annealed at different temperatures to develop nanocrystalline microstructure optimizing the soft magnetic properties. The magnetic properties of the as-spun and annealed ribbons were measured using a vibrating sample magnetometer and AC B-H loop tracer to acquire M_s of above 1.4 T in all as-spun ribbons. Among the alloys, Fe₈₄Si₁B₁₁Nb₃Cu₁ annealed at 545 °C showed the highest M_s of 2 T, which exceeds that of the conventional Finemet and other Fe-based nanocrystalline alloys. Full article

A survey of the cluster formation tendency and mechanism in transition metal-based glassy alloys is made with an emphasis on their manifestation in various physical properties. The cluster formation is partially inherited from the supercooling of the melt. However, it also develops due to the interaction between dissolved hydrogen and the frozen glassy structure. The glassy state as “cluster assembly” is regarded as a structural background for the interpretation of several anomalous concentration dependences of thermal and magnetic properties in these glasses. We will focus on the manifestation of alloying effects, the relation between irreversible and reversible structural relaxations both in the high, and low temperature range (observed near to the glass transition or after low temperature storage). The development of the cluster assembly is the consequence of the co-existence of various bonding types between the alloy components. These are brought together in the melt, ensuring sufficient glass-forming ability. The nucleation mechanism of the amorphous-nanocrystalline transformation is also explained as a cluster phenomenon, which significantly contributes to the evolution of magnetic ultra-softness in FINEMET-type alloys. Finally, the role of the quenched-in cluster structure in the mechanism of reversible and irreversible H-absorption is discussed. Irreversible H-induced structural rearrangements can appear as microphase separation in multicomponent systems, governed by the affinity difference between the metallic components and the absorbed hydrogen. This kind of H-induced reordering is responsible for the “volume activation” of amorphous H-storage alloys and it also causes the gradual breakdown of storage capacity during cyclic absorption–desorption steps. This article mainly focuses on the cluster phenomena in Fe-based glasses because of its unique combination of high mechanical strength, strong corrosion resistance, good thermal stability and excellent magnetic properties. Full article

This paper analyzes the dynamic magneto-mechanical response in magnetization-graded ferromagnetic materials (MGFM) comprised of high-permeability Finemet and traditional magnetostrictive materials. The theoretical modeling of the piezomagnetic coefficient that depends on the bias magnetic field of MGFM is proposed by using the nonlinear constitutive model of a piezomagnetic material, the magnetoelectric equivalent circuit method, and the simulation software Ansoft. The theoretical variation of piezomagnetic coefficients of MGFM on the bias magnetic field is in good agreement with the experiment. Using the piezomagnetic coefficient in the magnetoelectric voltage model, the theoretical longitudinal resonant magnetoelectric voltage coefficients have also been calculated, which are consistent with the experimental values. This theoretical analysis is beneficial to comprehensively understand the self-biased piezomagnetic response of MGFM, and to design magnetoelectric devices with MGFM. Full article

Applying tensile stresses on straight soft magnetic ribbons before core fabrication is a routine method of inducing magnetic anisotropy, while methods of stress annealing of ribbons after core winding are seldom explored. In this study, we utilize a novel approach to induce magnetic anisotropy by applying radial stresses on tape-wound cores of Fe_73.5Si_13.5B₉Cu₃Nb₁ (at. %) ribbon during crystallization heat treatment. The results show that while stress annealing does not change the structural characteristics of annealed samples, the magnetic anisotropies induced can increase to values ~3–5 times larger than the sample annealed in the absence of external stress. This increase in magnetic anisotropy energy is associated with ~25–50% decrease of magnetic inductance in the treated cores. These results suggest that the magnetic properties of nanocrystalline soft magnetic alloys can be effectively tuned by applying radial stresses. Full article