Nanocrystalline Soft Magnetic Materials Research Articles

Microstructure and magnetic properties of Nanomet compacted by spark plasma sintering

Nanocrystalline soft magnetic materials with high saturation polarization and low losses have a high potential in motor applications. Thus, toroidal cores were compacted by spark plasma sintering of flakes of the melt-spun Nanomet alloy Fe-Si-B-P-Cu. The thermal properties of the ribbons were analyzed by DSC to determine the crystallization temperatures. The influence of the initial powder and of the compacting parameters such as maximum temperature and dwell time on the density and the magnetic properties in DC and AC were investigated. An optimum temperature range of approximately 50 K was determined for good soft magnetic properties. An effect of the dwell time was not recognized in the observed range. By compacting flakes of different sizes, the maximum permeability can be adjusted in the range of up to 7000. The microstructure was observed by means of XRD and TEM in order to confirm the amorphous and nanocrystalline state, respectively. Using the Lorenz mode of the TEM, it was possible to calculate the magnetic domain wall width for the samples and compare the resulting calculated magnetic properties with the experiments.

Chemical surface modification for the preparation of MgO cladding to enhance magnetic properties of Fe-Si-Nb-B-Cu nanocrystalline soft magnetic composites

This study employed chemical synthesis and decomposition techniques to fabricate MgO insulation coating on the surface of nanocrystalline soft magnetic powder. It was found that this coating effectively suppresses the time lag effect in the magnetization process of soft magnetic materials under high-frequency alternating magnetic fields, consequently reducing the overall losses of soft magnetic composite materials by mitigating the time-dependent effects during magnetization. Specifically, at an MgO content of 0.8 wt%, the power losses of nanocrystalline soft magnetic composite materials decreased from 519.13 kW/m3 and 3665.78 kW/m3 to 277.69 kW/m3 and 2718.3 kW/m3 respectively, under alternating magnetic fields with magnetic induction strengths of 20 mT and frequencies of 1 MHz and 3 MHz. The MgO insulation coating effectively mitigated the relaxation phenomenon in the dynamic hysteresis loops of nanocrystalline soft magnetic composite materials within dynamic magnetic fields, reducing the adverse effects of internal eddy currents in high-frequency alternating magnetic fields, thereby confirming the close relationship between magnetic hysteresis losses and eddy current losses in soft magnetic composite materials. Additionally, with the increase in MgO content, there was a significant improvement in the quality factor of nanocrystalline soft magnetic composite materials, showing a decreasing trend in the imaginary part of the complex permeability, which reflects the magnitude of power losses. Furthermore, the positive response of MgO coating in enhancing DC superimposition performance and reducing inductance impedance values has been validated, underscoring its crucial role in improving the stability of circuit systems.

Origin of excess core loss in amorphous and nanocrystalline soft magnetic materials

Origin of excess core loss in amorphous and nanocrystalline soft magnetic materials

Application of Amorphous and Nanocrystalline Soft Magnetic Materials in Balanced-Force-Type Electromagnetic Relay.

The magnetic properties of soft magnetic materials, including their saturation magnetic induction strength and permeability, significantly affect the dynamic characteristics of electromagnetic relays. However, the soft materials most commonly used for relays in the magnetic conductive components of electromagnetic systems, such as electrical pure iron, limit further relay design improvement and optimization to a certain extent. Thus, this paper proposes the use of amorphous and nanocrystalline soft magnetic materials with good high-frequency magnetic properties in magnetic circuits. A wavelet analysis was conducted on the high-frequency components of the coil current while the relay operated, and the corresponding magnetic materials were selected. Considering the challenges in processing amorphous and nanocrystalline materials and collecting test data for the accuracy verification of simulation methods, we prepared a scaled-up prototype for use in dynamic characteristic tests. The simulation method was improved, yielding more accurate simulation results regarding the relay's dynamic characteristics. On this basis, six replacement schemes using amorphous and nanocrystalline materials were considered. The test results proved that this application could improve the relay's dynamic characteristics. Finally, a full-size sample with an iron core consisting of nanocrystalline alloy 1K107B was prepared, and the conclusions were verified in tests.

Recent advances in nanocrystalline soft magnetic materials: A critical review for way forward

In this report, shortcomings in the recent trend of alloy development in nanocrystalline soft magnetic materials are discussed critically and suggestions for further improvement of the soft magnetic properties are given. Owing to the strong power dependence of the coercivity on the mean grain size, much emphasis tends to be placed primarily on reducing the grain size. While this approach is quite effective in reducing the effect of the magnetocrystalline anisotropy (K1) and the domain wall pinning effect is suppressed, this approach may have limited impact on the domain wall damping which governs the dynamic energy dissipation. Thus, the core loss could not be reduced solely by nano-scale grain refinement. Our recent study shows that the excess loss is suppressed dramatically by reducing the saturation magnetostriction (λs) to near zero. Thus, much attention should be paid to λs in addition to the common grain refinement approach in nanocrystalline soft magnetic alloys.

Thermal Stability of Electrodeposited Fe-55wt%Ni Alloy and Effect of Low-Temperature Heat Treatment on Magnetic Properties

Electrodeposited nanocrystalline soft magnetic materials have emerged as one of the hottest research topics in the field of magnetic materials due to they are easy to implement in miniaturization, lightweight, and energy-saving of electronic devices. The thermal stability and grain growth process of electrodeposited Fe-55wt%Ni alloy were investigated. Results indicated that the grain growth was rapid at a temperature of about 678 K, while the exothermic peak appeared in DSC with an exothermic heat of about 12 ± 1 J g−1. The activation energy for grain growth was obtained through the optimized Kissinger equation and isothermal kinetics calculations, and the growth mechanism was evaluated based on the calculation results. Below 678 K, the activation energy required for grain growth was low, which implied the growth mechanism was the rearrangement of atoms at the grain boundary; Above 678 K, the growth mechanism was grain boundary diffusion. After the low-temperature heat treatment, the coercivity (H c) decreased and the saturation magnetization (M s) increased slightly, which was attributed to the reduction of internal stress and the ultra-fine nanocrystalline structure. The optimal heat treatment process was 573 K heat treatment for 5 h, where M s and H c of 160 emu g−1 and below 1 Oe, respectively.

In-situ observation of magnetic domain structures in nanocrystalline soft magnetic materials by differential-phase-contrast scanning transmission electron microscopy

In-situ observation of magnetic domain structures in nanocrystalline soft magnetic materials by differential-phase-contrast scanning transmission electron microscopy

Measurement and Simulation of Magnetic Properties of Nanocrystalline Alloys under High-Frequency Pulse Excitation

In order to broaden the application of nanocrystalline soft magnetic materials in electrical engineering under extreme conditions, nanocrystalline alloys must also have good characteristics under high-frequency and nonsinusoidal excitation. In this paper, the magnetic properties of Fe-based nanocrystalline alloys excited by high repetition frequency pulses were measured. Excitation frequency and duty cycles are two important factors in the study of magnetic properties under pulse excitation. With the amplitude of the pulse remaining constant, different local hysteresis curves were obtained by changing the frequency and duty cycle. The experimental results proved that the higher the frequency is and the smaller the duty cycle is, the narrower the local hysteresis loop is. Finally, the finite element method (FEM) was used to model the magnetic core coupling with an impulse circuit based on the measured magnetic properties. Compared with the experimental results, the simulation results showed that the field-circuit coupling analysis model can effectively reflect the influence law of the frequency and duty cycle on magnetic properties.

Magnetization controlled by crystallization in soft magnetic Fe-Si-B-P-Cu alloys.

Soft magnetic materials have low coercive fields and high permeability. Recently, nanocrystalline alloys obtained using annealing amorphous alloys have attracted much interest since nanocrystalline alloys with small grain sizes of tens of nanometers exhibit low coercive fields comparable to that of amorphous alloys. Since nanocrystalline soft magnetic materials attain remarkable soft magnetic properties by controlling the grain size, the crystal grains' microstructure has a substantial influence on the soft magnetic properties. In this research, we examined the magnetic properties of Fe-Si-B-P-Cu nanocrystalline soft magnetic alloys obtained by annealing amorphous alloys. During crystallization, the observation findings reveal the correlation between the generated microstructures and soft magnetic properties.

Role of magnetostriction on power losses in nanocrystalline soft magnets

Soft magnetic materials are key materials for the magnetic cores used in motors and generators. To improve the energy efficiency of magnetic cores, it is important to understand the mechanism of energy loss under oscillating magnetic fields. Here, we clarify the mechanism of energy loss in nanocrystalline soft magnetic materials (NSMMs), which are candidates for energy-efficient magnetic cores. To investigate the energy loss of an NSMM, it is necessary to consider the interaction between the magnetization and the crystal lattice, i.e., magnetostriction. However, the random distributions of crystalline axes in nanocrystals hinder magnetostriction calculation. We developed a micromagnetic simulation program by formulating the effective fields due to magnetostriction in randomly oriented nanocrystallites. We performed micromagnetic simulations of NSMMs under an oscillating magnetic field and found that the magnetic energy of the moving domain wall dissipates into the elastic energy of the crystal lattice through magnetostriction. These results can enable the design of highly energy-efficient NSMMs.

Nanocrystalline soft magnetic materials produced by continuous ultra-rapid annealing (CURA)

Ultra-Rapid Annealing (URA) is an effective means of producing Fe-rich nanocrystalline soft magnetic materials with desirable soft magnetic properties. However, compared to existing annealing techniques, URA presents many unique processing challenges that have so far limited its scalability. In this study, a novel Continuous Ultra-Rapid Annealing (CURA) technique is introduced. This technique is based on a reel-to-reel process and is considered suitable for industrial-scale production. The effectiveness of CURA is evaluated by comparing the microstructural and magnetic properties of a heating-rate-sensitive nanocrystalline (Fe0.8Co0.2)86B14 alloy produced by URA and CURA. It is seen that both techniques produce comparable soft magnetic properties and that the continuous annealing process is stable after a short settling time. A proof-of-concept electric motor containing a CURA prepared nanocrystalline stator core is also demonstrated and compared to an equivalent motor with a Fe-Si steel stator core. It is shown that the CURA production process can be used to produce magnetically soft nanocrystalline materials with complex geometries and that they can deliver increased performance in existing commercial applications.

Design issues of Rotational Single Sheet Tester for Fe-Based Nanocrystalline Alloys at High Frequencies

Measuring the vector magnetic properties of nanocrystalline soft magnetic materials at high frequencies is of great significance to the optimal design and energy saving of the electrical equipment. In this paper, some key design issues are discussed for a rotational single sheet tester (RSST) to further studied the Two-Dimensional (2D) magnetic properties of nanocrystalline alloys in the kilohertz range. Firstly, the magnetization uniformity of the testing sample is analyzed and discussed considering the stray field. Secondly, the magnetizer

Nanocrystallization, magnetic properties and bending ductility of antiferromagnetic Mn-doped FeSiBCuPC alloys induced by micro-compressive stress annealing

Insufficient amorphous forming ability (AFA) and thermal instability have always been the bottleneck restricting the application of high Fe content iron-based nanocrystalline soft magnetic materials. In this work, the effects of micro-compressive stress annealing (MCSA) on microstructure, soft magnetic and mechanical properties of high Fe content FeSiBCuPCMn alloys were systematically investigated. We demonstrate that Mn doping effectively increases the AFA of the alloys and improves the thermal stability of the amorphous matrix. The change of coercivity (Hc) is closely related to the grain size, which depends on the Mn content and annealing process. It clearly shows that a small amount of Mn doping (≤3 at%) and MCSA can inhibit the excessive growth of α-Fe grains and reduce the grain size. Moreover, the low Mn-doped amorphous alloys exhibit good bending ductility even after annealing at appropriate conditions. After MCS-annealing at 420 °C for 10 min, the Mn-doped Fe85−xSi1.3B9P4Cu0.5C0.2Mnx (≤3 at%) nanocrystalline alloys exhibit comprehensive and excellent soft magnetic and mechanical properties, such as high Bs of 1.79–1.87 T, low Hc of 4.6–9.9 A/m and low Hv of 737–867.

Mineral oil based CuO nanofluid-immersed transformers analysis concerning the efficacy of nanocrystalline alloy core in reduction of losses and HST

Electromagnetic and thermal evaluation of transformers are required for better acquaintance with detailed and complex behaviors of the system components as well as accurate description of the corresponding magnetic and thermal performances. Hence, this paper is devoted to a comprehensive study of the impact of CuO nanoparticles on cooling performance enhancement of a three-phase transformer. Besides, as determination of proper values for heat generation rate of the transformer core is indispensable for thermal modeling, the core losses are acquired through electromagnetic modeling as an essential step. The results derived from the transformer with silicon steel core are compared with the case in which a type of nanocrystalline soft magnetic core material, Finemet, is used. In this paper, 3D simulations are performed for electromagnetic and heat transfer analysis of the transformer. The results gained for nanocrystalline core indicate its superior efficiency in lessening the core losses due to the drastic improvement found in its magnetic and thermal characteristics compared to conventional cores used in previous works. It also becomes apparent that the use of CuO nanoparticles in the pure oil as a novel approach leads to lower hotspot temperature accompanied by notable decrease in the average and maximum temperatures of the fluid. Mean heat transfer coefficients of the oil with and without nanoparticles are finally checked against experimental values to show the simulation results preciousness.

Nanocrystalline Soft Magnetic Iron-Based Materials from Liquid State to Ready Product.

The review is devoted to the analysis of physical processes occurring at different stages of production and application of nanocrystalline soft magnetic materials based on Fe–Si–B doped with various chemical elements. The temperature dependences of the kinematic viscosity showed that above a critical temperature, the viscosity of multicomponent melts at the cooling stage does not coincide with the viscosity at the heating stage. Above the critical temperature, the structure of the melt is more homogeneous, the amorphous precursor from such a melt has greater plasticity and enthalpy of crystallization and, after nanocrystallization, the material has a higher permeability. The most effective inhibitor elements are insoluble in α-Fe and form a smoothed peak of heat release during crystallization. On the other hand, the finest nanograins and the highest permeability are achieved at a narrow high-temperature peak of heat release. The cluster magnetic structure of a nanocrystalline material is the cause of magnetic inhomogeneity, which affects the shape of the magnetic hysteresis loop and core losses.

Heating rate dependence of coercivity and microstructure of Fe–B–P–Cu nanocrystalline soft magnetic materials

The nanocrystalline structure and soft magnetic properties of melt-spun Fe–B–P–Cu ribbons are largely influenced by heating rates for crystallization of amorphous precursors. In this study, we investigated the structure and soft magnetic properties of Fe84.8B4.9P9.5Cu0.8 (P-rich) and Fe84.8B10.9P3.5Cu0.8 (B-rich) melt-spun ribbons crystallized at two different heating rates, 0.67 K/s and 6.7 K/s, using transmission electron microscopy (TEM) and atom probe tomography (APT). The P-rich ribbon shows smaller coercivity regardless of the heating rates, while the B-rich ribbon shows large heating rate dependence of the coercivity. APT analyses have revealed that the size of Cu clusters in the P-rich nanocrystalline ribbon is larger than that in the B-rich nanocrystalline ribbon while their number densities are nearly the same. Also, the high heating rate led to a larger size and higher Cu concentration of the Cu clusters in both samples, indicating that the Cu clusters are effective as nuclei for α-Fe only when they are larger than a critical size. The solute partitioning behaviors between α-Fe and residual amorphous phase determined by APT analyses are consistent with the tie-lines between α-Fe and liquid phase in a calculated Fe–P–B ternary phase diagram. P was found to segregate at amorphous/α-Fe interface, suggesting the grain growth is controlled by the volume diffusion of P in the amorphous phase during their crystallization process.

Effect of latent heat during primary crystallization on the nanostructural formation process in nanocrystalline soft magnetic materials

Nanocrystalline soft magnetic materials are known to be prepared by primary crystallization of Fe-based amorphous precursors. Since the crystallization reaction is exothermic, the amorphous precursor may experience a temporary rise in its temperature relative to its surroundings during the process of nanocrystallization. Given the typical latent heat of primary crystallization (∼ 100 kJ/kg), this temperature rise may exceed hundreds of degrees if not adequately controlled and thus, lead to the formation of unwanted magnetically hard compounds. This effect is generally small for isolated ribbons annealed with a moderate heating rate. However, the recent adoption of high heating rates and short annealing times has caused the self-heating effect to become relevant even for small sample sizes. In this work, the effect of self-heating on the microstructure and magnetic properties of nanocrystalline Fe86B14 is investigated. It is found that magnetically hard Fe-B compounds cannot be avoided when annealing under vacuum in an infrared furnace with a heating rate ≥3 K/s due to the self-heating effect. However, the high thermal conductivity of the copper blocks used by the ultra-rapid annealing process can successfully prevent a self-heating induced temperature rise during annealing, avoiding unwanted compound formation. Finite Element Analysis is also used for predicting the extent of self-heating during infrared annealing.

A Circumferential Coupled Dipole-Coil Magnetic Coupler for Autonomous Underwater Vehicles Wireless Charging Applications

Inductive power transfer is a practical approach to recharging the autonomous underwater vehicles (AUVs). The performance of the magnetic coupler determines the system transfer capacity. The annular magnetic coupler is widely utilized in the underwater wireless charging system. However, this magnetic coupler has limitations on magnetic field distribution. The flux linkage occupies the center of the AUV, and hence, the electronics inside the AUV are susceptible to electromagnetic interference. Additionally, the weight of the annular magnetic coupler greatly increases the burden on AUV power supply. In this paper, the magnetic coupler structure evolution is analyzed and a dipole-coil-based magnetic coupler with a novel circumferential coupling manner is presented. The magnetic flux is perfectly confined by the coupling manner, and the magnetic coupler weight is reduced by dimension optimization. To implement the magnetic coupler, the Fe-based nanocrystalline soft magnetic material is taken into consideration. To validate the proposal, a wireless charging system is built. Experimental results show that the system transfers 630W under water with a DC-DC efficiency of 89.7%.

Polarization analysis in small-angle neutron scattering with a transportable neutron spin filter based on polarized protons

We present the status of development of a novel neutron spin filter based on the strong spin dependence of the neutron scattering on protons. Using photo-excited triplet states for the dynamic nuclear polarization (DNP) process, proton polarization values of 80% can now be achieved in pentacene doped single crystals of naphthalene at a field of 0.36 T in a simple helium flow cryostat. Careful sample preparation lead to extremely long polarization decay times under moderate conditions that allowed us to develop a transportable device. The filter is polarized in the lab under well controlled conditions and is then transferred to the neutron beam line where it can be operated during several days with almost constant polarization while requiring only a minimum of equipment. We describe briefly the main features of the spin filter and its use as a spin analyzer in a small-angle neutron scattering (SANS) experiment probing the magnetic structure of a nanocrystalline soft magnetic material. Furthermore the procedure for performing the background and spin leakage corrections of the neutron data is outlined in detail.

Magnetoimpedance Effect in the Ribbon-Based Patterned Soft Ferromagnetic Meander-Shaped Elements for Sensor Application.

Amorphous and nanocrystalline soft magnetic materials have attracted much attention in the area of sensor applications. In this work, the magnetoimpedance (MI) effect of patterned soft ferromagnetic meander-shaped sensor elements has been investigated. They were fabricated starting from the cobalt-based amorphous ribbon using the lithography technique and chemical etching. Three-turn (S1: spacing s = 50 μm, width w = 300 μm, length l = 5 mm; S2: spacing s = 50 μm, width w = 400 μm, length l = 5 mm) and six-turn (S3: s = 40 μm, w = 250 μm, length l = 5 mm; S4: s = 40 μm, w = 250 μm and l = 8 mm) meanders were designed. The ‘n’ shaped meander part was denominated as “one turn”. The S4 meander possesses a maximum MI ratio calculated for the total impedance ΔZ/Z ≈ 250% with a sensitivity of about 36%/Oe (for the frequency of about 45 MHz), and an MI ratio calculated for the real part of the total impedance ΔR/R ≈ 250% with the sensitivity of about 32%/Oe (for the frequency of 50 MHz). Chemical etching and the length of the samples had a strong impact on the surface magnetic properties and the magnetoimpedance. A comparative analysis of the surface magnetic properties obtained by the magneto-optical Kerr technique and MI data shows that the designed ferromagnetic meander-shaped sensor elements can be recommended for high frequency sensor applications focused on the large drop analysis. Here we understand a single large drop as the water-based sample to analyze, placed onto the surface of the MI sensor element either by microsyringe (volue range 0.5–500 μL) or automatic dispenser (volume range 0.1–50 mL).