Soft Ferromagnetic Materials Research Articles

Periodically spaced collinear cracks in a soft ferromagnetic material under a uniform magnetic field

This paper aims at a fundamental perspective of multiple cracks’ interaction on the fracture behavior of magnetoelastic materials. A theoretical study is performed on a soft ferromagnetic solid weakened by an array of periodic cracks under an in-plane magnetic loading. By using the conformal mapping technique and the analytic function boundary value theory, a rigorous analytical solution of the magnetic and stress fields is obtained, and the closed-form expressions for the field intensity factors are presented. Numerical examples of magnetically impermeable and permeable cracks are studied to reveal the relationship of the mode-I stress intensity factor with the period ratio of the cracks, the surrounding medium, and the applied magnetic loading. The analytical solution in this study can serve as a theoretical benchmark for the fracture problem of a magnetoelastic solid containing multiple defects.

A general nonlinear magneto-elastic coupled constitutive model for soft ferromagnetic materials

In this study, a new general nonlinear magneto-elastic coupled constitutive model was proposed for soft ferromagnetic materials under magnetic field and pre-stress. The model is based on thermodynamic theory of magnetic materials and Jiles theory on magnetomechanical effect, considering demagnetization field. This model can accurately predict the changes of magnetostrictive strain and magnetization under pre-stress; in particular, it can obviously predict the nonlinear change of magnetostrictive strain according to compressive pre-stress. In addition, this model is concise by not including the inverse function of magnetization relationship and the piecewise function of stress in its mathematical form and can be degenerated to the previous general constitutive model for giant magnetostrictive materials. The prediction result by this model is well-consistent with experimental data. In comparison with the existing constitutive models for soft ferromagnetic materials, this model was demonstrated to have obviously-improved prediction accuracy, particularly in the compressive state. In conclusion, the proposed model can fully describe the effect of pre-stress on magnetostrictive strain and magnetization and the effects of magnetic field and pre-stress on Young’s modulus and relative magnetic permeability, reflecting the effect of demagnetization field on magnetomechanical characteristics.

Modeling and numerical simulation of soft ferromagnetic materials used in electrical machinery

The soft ferromagnetic materials are usually used to conduct the magnetic induction flux in electrical devices. These materials create currents known as Foucault currents affecting the efficiency and performance of these devices: the resistivity and magnetization decrease, and magnetic losses increase. The Soft Magnetic Composite (SMC), based on the metallurgy of iron powder which are used to improve the resistivity by restricting the Foucault currents flow, and this is due to the insulation of iron particles. However, the production process of these materials creates parasitic air gaps distributed throughout the volume of the magnetic circuit leading to a significant reducing of the relative permeability of the material. In this work, we study the various factors that may affect the performance of SMC materials, and we compare these materials with other of the same category.

Magnetic and dielectric properties of solid solutions (1–x)BiFeO3–xYMnO3 multiferroics

The magnetic hysteresis loops in fields ranging from 0 to ± 2.5 kOe and the dielectric permittivity ɛ (measured at 1 kHz, 1 MHz, and 8.3 GHz) of composite multiferroic materials (1–х)BiFeO3–xYMnO3 (0 ≤ x ≤ 0,5) have been studied. Ceramic solid solution samples were prepared using nitrate technology. It was found that the (1–x)BiFeO3–xYMnO3 (0.1 < x < 0.5) compounds are magnetically soft ferromagnetic materials that are sensitive to weak magnetic fields. The coercive field Hc is ∼20–32 Oe. Maximum magnetization was observed for samples with х = 0.35. For samples with 0 ≤ x ≤ 0.4 at Т = 300 K and a frequency of 1 kHz, ɛ ∼17.6–248.6, at a frequency of 1 MHz ɛ ∼7.8–63.2, and at a frequency of 8.3 GHz, ɛ ∼4 ± 0.3.

Finite-Element Formulations for Systems With High-Temperature Superconductors

In this article, we consider finite-element models for high-temperature superconductors and compare two dual formulations, either magnetic-field conforming or magnetic-flux-density conforming. The electrical resistivity of superconductors is described by a power law and is strongly nonlinear. We compare the accuracy and the efficiency of the dual formulations by starting from simple considerations on the concavity/convexity of the constitutive law involved in each case. We then study the numerical behavior of each formulation in one-, two-, and three-dimensional problems and compare their results against benchmarks. We draw general recommendations for the choice of a formulation, an iteration scheme for treating the corresponding linearized constitutive law, and a time-stepping extrapolation scheme. This approach is extended to soft ferromagnetic materials with a saturation law. Since the outcome of our analysis shows that recommended formulations for treating ferromagnets are just the opposite of those for treating superconductors, we suggest a coupled formulation for systems where both types of materials are present. The coupled formulation is shown to be accurate and more efficient than single formulations applied indistinctly to all materials.

Phase evolution and magnetic properties of Dy3Fe5+xO12−x nanocrystalline powders: A choice of fuel approach

Garnet based Dy3Fe5O12 nanostructured materials have gained considerable attention in recent years due to their potential technological applications. Garnet type structured Dy3Fe5+xO12−x nanocrystalline powders were synthesized via propellant chemistry route. Single and mixed-fuel approaches were employed in the solution combustion process. Annealing the combusted powders at 1000 °C for 6 h resulted in nanocrystalline powders which are about 95% by weight garnet type and 5% orthorhombic DyFeO3. This was confirmed from powder X-ray diffraction studies through Rietveld analysis. The solution combustion mechanisms involved in the formation of Dy3Fe5+xO12−x nanocrystalline powders are briefly discussed. Scanning electron microscopy and energy dispersive X-ray spectroscopy studies revealed that the choice of fuel approach in the synthesis process affected the morphology and elemental composition. Raman spectroscopic studies revealed the existence of two magnon and two phonon scattering peaks rarely observed for garnet based Dy3Fe5O12. The synthesized Dy3Fe5+xO12−x nanocrystalline powders displayed ferromagnetic behavior. The saturation and remanent magnetization varied between 2.67-8.29 and 1.08–2.64 emu/g respectively, while the corecivities were in the order of few hundreds oersteds, characteristic of a soft ferromagnetic material. It is suggested that Dy3Fe5+xO12−x nanocrystalline powders with different magnetic properties could be tailored for different requirements.

Design and Analysis of a Novel CPT System with Soft Ferromagnetic Material Cores and Electromagnetic Resonant Coupling for Evs

This paper describes a novel contactless power transfer (CPT) system with geometrically improved H-shape ferromagnetic cores and electromagnetically prospective modelling analysis methods for wireless power transmitting (WPT) applications of electric vehicles (EVs). A CPT prototype, using optimized H-shaped magnetic couplers and series-to-series (SS) compensation, is proposed to address and ensure the maximization of system efficiency, power transfer ratings, and air gaps of coupling coils. By focusing on the main factors such as various system operating frequencies, different geometric designs of coils, changeable inductive coupling distances, electromagnetic field performances and actual phase angle deviations when the inductive coupling system tends to be stable with its waveforms, this small-sized H-shape CPT system has been analytically considered and modelled in a finite-element method (FEM) environment, resulting in a maximum system efficiency of 59.5%, a coil transmitting efficiency of 83.8% and a maximum power output of 42.81 kW on the load end when the resonant coupling of CPT system tends to occur within a range of calculated resonant frequencies, with an air gap of 10 mm. Moreover, the system efficiency and coil transmitting efficiency can reach 47.75% and 77.22%, respectively, and the highest RMS real power to load can achieve 31.95 kW with an air gap of 20 mm. Besides, with an air gap of 30mm, this H-shape CPT system is measured to output 20.39-kW RMS power, along with the maximum system efficiency and coil efficiency of 41.78% and 63.23%, respectively. Furthermore, the improvements of flux linkage, magnetic flux density regarding the actual electromagnetic performance produced and the issues on the calculated natural resonant frequencies have been studied by result analysis and comparison of electromagnetic field parameters generated. In addition, the current limitations and further design considerations have been discussed in this paper.

Experimental Observation of Exchange-Driven Chiral Effects in Curvilinear Magnetism.

The main origin of the chiral symmetry breaking and, thus, for the magnetochiral effects in magnetic materials is associated with an antisymmetric exchange interaction, the intrinsic Dzyaloshinskii-Moriya interaction (DMI). Recently, numerous inspiring theoretical works predict that the bending of a thin film to a curved surface is often sufficient to induce similar chiral effects. However, these originate from the exchange or magnetostatic interactions and can stabilize noncollinear magnetic structures or influence spin-wave propagation. Here, we demonstrate that curvature-induced chiral effects are experimentally observable rather than theoretical abstraction and are present even in conventional soft ferromagnetic materials. We show that, by measuring the depinning field of domain walls in the simplest possible curve, aflat parabolic stripe, the effective exchange-driven DMI interaction constant can be quantified. Remarkably, its value can be as high as the interfacial DMI constant for thin films and can be tuned by the parabola's curvature.

Visualization of the Rolling Contact Fatigue Cracks in Rail Tracks with a Magnetooptical Sensor

The rolling contact fatigue cracks (RCF), produced at the surface of the rail tracks, can be detected using a magnetooptical (MO) sensor. Rail tracks are carbon steels with pearlite microstructure. This microstructure has a lamellar texture composed of alternating layers of ferrite and cementite. Both phases are soft ferromagnetic materials at room temperature. If an external magnetic field is applied on the surface of a rail track, the reduced magnetic permeability causes a magnetic leakage field above the cracks. When the external magnetic field is removed, in most cases, a residual stray magnetic field remains above the cracks. When a MO sensor is placed on the surface of the rail track, the sudden change of the stray remanent magnetic field near a crack, yields a significant rotation of the polarization plane of the reflected light, resulting in high MO contrast, exactly above the cracks. Using a polished surface and a cross-section from the head of the rail track, we succeeded in visualizing the RCF cracks in the laboratory. The RCF cracks can also be detected on the surface of the rail track, in field measurements, using a portable commercial polarized light microscope equipped with a MO sensor. Finally, we use computer vision methods, to automatically detect the RCF cracks, using video recorded by displacing the portable microscopy with the MO sensor, on the surface of the rail tracks. We tested an unsupervised automatic crack detection algorithm, which exploits the tubular contrast of the RCF cracks to pinpoint the pixels that correspond to them.

Influence of Al doping on the structure and properties of Fe2O3 thin films: high transparency, wide band gap, ferromagnetic behavior

This paper presents a detailed study of structural, morphological, optical, transport and magnetic properties of aluminum (Al) doped ferric oxide (Fe2O3) thin films deposited onto glass substrates at 350 °C by spray pyrolysis technique. Al concentration was varied from 0 to 10 atomic percentages (at%). The x-ray diffraction patterns of Al doped Fe2O3 thin films showed the corundum structure with the predominant (104) peak. In scanning electron micrographs, the surfaces of the Al doped Fe2O3 thin films were observed to be formed of nanoparticles. Al doped Fe2O3 thin films were transparent in the visible to near infrared region. Transmittance and optical band gap of Al doped Fe2O3 thin films increased with the rise of Al concentration up to 6 at% and then decreased for the 8 and 10 at% Al concentrations. Al doped Fe2O3 thin films showed n-type electrical conductivity with high mobility and Hall coefficient. Electrical resistivity of Al doped Fe2O3 thin films varied from 5.67 × 105 to 8.92 × 105 Ω-cm and carrier concentration was found between 1.56 × 1017 and 8.64 × 1017 cm−3. Hysteresis loops of Al doped Fe2O3 thin films recorded at room temperature matched with the nature of soft ferromagnetic materials and the saturation magnetization decreased with Al concentration in Fe2O3 thin films.

Magnetic and electrical properties of Fe90Ta10 thin films

Abstract Fe 90 Ta 10 (Fe-Ta) thin films, deposited using a pulsed laser deposition (PLD) method, have been found to exhibit characteristics of a soft ferromagnetic material with very low coercivities (1-10 mT) and saturation magnetization ∼ 16 × 10 5 A/m. Our temperature dependent magnetization data at several fields (0.1 – 3 T) have conclusively detected the anharmonic term in the magnon dispersion relation. Moreover, the rigid-band model for metallic alloys can predict correctly the magnetic moment of ∼ 2 µ B as found by us from the above magnetization data of Fe 90 Ta 10 . We have also observed an Extraordinary Hall Effect (EHE) in these films. The extrinsic quantum mechanical side-jump mechanism as well as the intrinsic mechanism (due to the Berry phase curvatures) are responsible for the EHE varying here as the square of the electrical resistivity. Thus, our interpretation of the data at every stage is backed by theoretical considerations.

Enhancement of the Critical Current of Bi-2223 Superconducting Coil by Using of Soft Ferromagnetic Material

The effects of soft ferromagnetic material placed nearby the high-Tc Bi-2223 coil is analyzed. Electro-magnetic simulation have been carried out to find the distributions of the magnetic field of the Bi-2223 coil. The used soft ferromagnetic material could change the distribution of the Bi-2223 coil’s magnetic field, and the transport capability of the Bi-2223 coil changes consequently. According to the simulation results, the thickness of the soft ferromagnetic material plate shows a notable effect on the coil, and the position and width of the plate could present negative effects. Experimental result of a Bi-2223 coil with B30P105 silicon steel plate is consistent with the simulation conclusions, and the critical current of the developed Bi-2223 coil could achieve an improvement of 15% by using of a piece of silicon steel plate with a thickness of 0.3 mm.

De-embedding zero-field signal in high-frequency magneto-impedance measurements of soft ferromagnetic materials

Abstract Devices based on soft ferromagnetic materials are promising for high-frequency flexible electronics. Especially, wide-range tunable ferromagnetic resonance response of ferromagnetic microwires and ribbons can be functionalized in the form of magneto-impedance sensors in stretchable, bendable and twistable environments. A vector network analyzer calibrated by standard techniques is required to characterize the high-frequency properties of such devices. However, most of the calibration techniques necessitate calculations, computer simulations, and/or fabricating calibration kits in the shape of various test fixtures. Here, we employ a fixture calibration method for high-frequency (up to 4 GHz) impedance measurements of CoFeSiB microwires and melt-spun ribbons taking zero applied magnetic field as the reference. This method is based on a virtual de-embedding procedure, in which a reference signal is subtracted from all the subsequent measurements, which reduces the time for the total calibration procedure down to few minutes. Applications of the method are not limited to the cases where applied magnetic field varies. Any external parameter (strain, temperature, pressure etc.) that can change the impedance is allowed by this method.

Mагнитные и диэлектрические свойства мультиферроиков (1-x)BiFeO-=SUB=-3-=/SUB=--xYMnO-=SUB=-3-=/SUB=-

AbstractMagnetic hysteresis loops obtained in the fields from 0 to ±2.5 kOe and dielectric permittivity ε (at 1 kHz, 1 MHz, and 8.3 GHz) of (1 – x )BiFeO_3– x YMnO_3 composite multiferroics (0 ≤ x ≤ 0.5) were studied. Ceramic samples of solid solutions were made by the nitrate process. Compositions (1 – x )BiFeO_3– x YMnO_3 with 0.1 ≤ x ≤ 0.5 were found to be soft ferromagnetic materials sensitive to weak magnetic fields. Coercive field H _ c is about 20–32 Oe for these samples. The maximal magnetization was observed in the sample having x = 0.35. For the samples with 0 ≤ x ≤ 0.4 at T = 300 K, the permittivity was ε ~ 17.6–248.6 at the frequency of 1 kHz, 7.8–63.2 at 1 MHz, and 4 ± 0.3 at 8.3 GHz.

Spin-orbit torques acting upon a perpendicularly magnetized Py layer

We show that Py, a commonly used soft ferromagnetic material with weak anisotropy, can become perpendicularly magnetized while depositing on a Ta buffer layer with Hf or Zr insertion layers (ILs) and an MgO capping layer. By using two different approaches, namely, harmonic voltage measurement and hysteresis loop shift measurement, the dampinglike spin-orbit torque (DL-SOT) efficiencies from Ta/IL/Py/IL/MgO magnetic heterostructures with perpendicular magnetic anisotropy are characterized. We find that though Ta has a significant spin Hall effect, the DL-SOT efficiencies are small in systems with the Ta/Py interface compared to that obtained from the control sample with the traditional Ta/CoFeB interface. Our results indicate that the spin transparency for the Ta/Py interface is much less than that for the Ta/CoFeB interface, which might be related to the variation of spin mixing conductance for different interfaces.

Effect of Uniaxial Anisotropy and Demagnetizing Effects on the Magnetic Behavior of Polycrystalline Gadolinium

Gadolinium (Gd) is a soft ferromagnetic material with uniaxial magnetic anisotropy. The anisotropy is responsible for some magnetic features that are quite different from those observed in most common ferromagnetic materials. Polycrystalline Gd exhibits thermal hysteresis in which the memory of past magnetic history is stored in the buildup of magnetic charge density around grain boundaries on cooling in magnetic fields from above the spin-reorientation temperature $T_{\text {SR}} \sim 235$ K, in the range where the uniaxial anisotropy is positive. This has the effect of narrowing domain walls (DWs) that interact more strongly with defects, such as grain boundaries. Below $T_{\text {SR}}$ , where the negative uniaxial anisotropy is increasing in magnitude with decreasing T, the magnetic susceptibility increases by orders of magnitude. Negative uniaxial anisotropy makes it easier for DWs to move past defects, such as grain boundaries, because wider Neel walls are favored over narrower Bloch walls. Magneto-thermal measurement protocols are used to study the effect of cooling in a field $\mu _{0}H = -50$ mT to 5 K and then measuring at lower constant fields, typically $\mu _{0}H = 3.5$ mT, from 5 to 380 K. The protocols permit the extraction of the temperature dependencies of the susceptibility, which depends on anisotropy, and of the frozen fraction of the magnetization, which consists of two parts. One part freezes upon field cooling below $T = 100$ K, and a harder one freezes above 250 K. On first warming, the former unfreezes below 100 K, while the latter unfreezes above 250 K.

Integrated Compensation and Rotation Alignment for Three-Axis Magnetic Sensors Array

The differential magnetic gradient tensor system is usually constructed from the three-axis magnetic sensor array, thus making the misalignment error between the sensors become the main source of the measurement error. In addition, the sensor axial biases, scale factors, non-orthogonality, and external magnetic distortion fields severely affect the tensor measurement accuracy simultaneously when the system is applied as a strapdown device. Considering the systematic error and the magnetic interferences, the integrated error coefficient matrix and the integrated bias vector is constructed according to the magnetic field mathematical model of the hard and soft ferromagnetic material, and the integrated compensation model of the sensor is established based on the least-squares (LS) ellipsoid fitting. The rotation matrixes of the roll, pitch and yaw conversion of the sensors are constructed, and the misalignment error calibration model of the sensor array is obtained. The two linear equations that rotate only about one axis are extracted and the misaligned angles are estimated by the LS method to calibrate the tensor system. Simulation and experimental results show that the proposed method compensates the integrated error of magnetic sensor effectively, and requires only a few measurement data to align the sensor array accurately, which efficiently improves the measurement accuracy of the magnetic gradient tensor system.

High-Temperature Magnetic Characterization Using an Adapted Epstein Frame

The most common method for the electrical steel sheet characterization uses the Epstein frame. However, in the case of high-temperature characterization, the standard Epstein frame is not adapted to high temperature measurements. This paper deals with the design of an Epstein frame adapted for high temperature measurements, up to 600 °C. In a first step, the results at ambient temperature obtained between the normalized Epstein frame and the high-temperature device for different frequencies are compared in order to validate the new frame. The second step is dedicated to the characterization of soft ferromagnetic materials in high temperature, up to 600 °C and for different frequencies. Moreover, the effect of sheet thickness on their behavior has been studied at high temperatures. The obtained measurement results confirm the strong influence of both temperature and thickness on power losses.

Asymptotic Derivation of a Linear Plate Model for Soft Ferromagnetic Materials

We apply the asymptotic expansion method by P.G. Ciarlet to obtain a Kirchhoff-Love-type plate model for a linear soft ferromagnetic material. We also give a mathematical justification of the obtained model by means of a strong convergence result .

Dynamic properties of micro-magnetic noise in soft ferromagnetic materials

Dynamic response of magnetic hysteresis, magnetic Barkhausen noise and magneto-acoustic emission in a soft ribbon and electrical steels was studied comprehensively. The measurements were performed under controllable magnetization conditions: sinusoidal/triangular waveforms of the magnetic induction and a triangular waveform of the magnetic field. Magnetizing frequency was varied in a wide range: fmag=0.5–500 and 0.5–100 Hz for the ribbon and the electrical steels, respectively. Magnetization amplitude was fixed on a near-saturation level Hmax≃100 A/m. Barkhausen noise signal was detected by a sample-wrapping/surface-mounted coil and differently filtered. It was found that intensity of the Barkhausen noise rises approximately as a square root function of the magnetizing frequency. Whereas, level of the magneto-acoustic emission follows the hysteresis loss trend with an additional linear term (classical loss component).