Showing papers on "Saturation (magnetic) published in 2021"

Exploration of crystal structure, magnetic and dielectric properties of titanium-barium hexaferrites

Abstract: The BaFe12-xTixO19 hexaferrites up to x = 3.00 were extended. XRD patterns were Rietveld fitted for P63/mmc (no. 194) space group and the unit cell parameters were defined. The a parameter and V volume of unit cell change non-monotonically with × while the c parameter has linear behavior. The Ti4+ cations substitute the Fe3+ cations in the 2a, 4fVI and 12 k octahedral positions. This is confirmed by the Mossbauer spectroscopy. Ms spontaneous magnetization was determined with the law of approach to saturation from field magnetization at 5 K and 300 K. The e/ real part of the permittivity increases constantly with increasing temperature and decreases with frequency. The main objective of this study is an interpretation of the magnetic and dielectric properties of the titanium-barium hexaferrites which has performed in frame of breakdown of Fe3+ - O2– - Fe3+/2+(Ti4+) indirect superexchange interactions taking into account the positions occupation.

Research on Novel Flexible High-Saturation Nanocrystalline Cores for Wireless Charging Systems of Electric Vehicles

Abstract: The ferrite core plays an essential role in coupling enhancement and magnetic shielding for the wireless power transfer of electric vehicles. However, ferrite has apparent defects, such as a low saturation and brittleness, especially at the vehicle side. Therefore, a novel flexible nanocrystalline core is proposed in this article, which has high flexibility and high saturation limits. However, the nanocrystalline core has a large eddy current under 85-kHz excitation, so the refinement crushing process and alternating seamless stitching process are adopted to reduce the eddy loss. The feasibility of the improvement process is preliminarily verified via finite element simulations, and four nanocrystalline cores with different permeabilities are obtained. Through static parameter measurements and 7.7-kW loading tests, the modified nanocrystalline cores achieve excellent results. Based on the above, the nanocrystalline core with the best performance is further selected for an anti-saturation test and leakage measurement at 11 kW. Even when the thickness is reduced to 2 mm, the ac–ac efficiency remains 97.408%. The maximum core temperature is only 80.9 °C, and the flux leakage completely satisfies the limit requirements of ICNIRP 2010. In contrast, the ferrite core cannot withstand the impact of a strong alternating field and fails.

Effects of Topological Defect on the Energy Spectra and Thermo-magnetic Properties of CO Diatomic Molecule

Abstract: Confinement effects of Aharonov–Bohm (AB) flux and magnetic fields with topological defect on $$CO$$ diatomic molecule modeled by screened modified Kratzer potential is investigated in this paper. The all-encompassing effects of the fields and topological defect result in a strongly repulsive system. We discover that the collective effect of the fields and defect is more intense than the lone and dual effect and consequently there is a substantial shift in the bound state energy of the system. We also find that to sustain a low-energy medium for the molecule modeled by SMKP, the topological defect and weak AB field are required, whereas the magnetic field can be used as a control parameter or enhancer. The effects of the topological defect and magnetic and AB fields on the thermal and magnetic properties of the system are duly analyzed. We observe that the system tends to exhibit both a paramagnetic and diamagnetic behavior for weak and intense magnetic field, respectively, and some sort of saturation at high magnetic field. To further validate our findings, we map our result to 3D and a comparison of our results with what one obtains in literature reveals an excellent agreement.

Large and sensitive magnetostriction in ferromagnetic composites with nanodispersive precipitates

Abstract: Large and sensitive magnetostriction (large strain induced by small magnetic fields) is highly desired for applications of magnetostrictive materials. However, it is difficult to simultaneously improve magnetostriction and reduce the switching field because magnetostriction and the switching field are both proportional to the magnetocrystalline anisotropy. To solve this fundamental challenge, we report that introducing tetragonal nanoprecipitates into a cubic matrix can facilitate large and sensitive magnetostriction even in random polycrystals. As exhibited in a proof-of-principle reference, Fe–Ga alloys, the figure of merit—defined by the saturation magnetostriction over the magnetocrystalline anisotropy constant—can be enhanced by over 5-fold through optimum aging of the solution-treated precursor. On the one hand, the aging-induced nanodispersive face-centered tetragonal (FCT) precipitates create local tetragonal distortion of the body-centered cubic (BCC) matrix, substantially enhancing the saturation magnetostriction to be comparable to that of single crystal materials. On the other hand, these precipitates randomly couple with the matrix at the nanoscale, resulting in the collapse of net magnetocrystalline anisotropy. Our findings not only provide a simple and feasible approach to enhance the magnetostriction performance of random polycrystalline ferromagnets but also provide important insights toward understanding the mechanism of heterogeneous magnetostriction. The performance of materials that convert magnetic to mechanical energy and vice versa has been improved by introducing nanoprecipitates into their structure. Magnetostrictive materials can expand or contract under the influence of an external magnetic field. This property makes them useful for low-power sensors and energy harvesting. Simultaneously optimizing both the size of the magnetostrictive effect and the material’s sensitivity to small magnetic fields is difficult because increasing one effect tends to decrease the other. Tianyu Ma, Xi’an Jiaotong University, China, and Xiaobing Ren, National Institute for Materials Science, Tsukuba, Japan, and co-workers developed an approach to solve this problem by introducing tiny imperfections into a ferromagnetic alloy. By changing the atomic structure of small regions within the alloy iron−gallium, the researchers were able to achieve a five-fold improvement in the material’s magnetostrictive performance. a Aging-time dependent saturation magnetostriction for Fe73Ga27 random polycrystals. Bright-field images for the b 1373 K-quenched, c 1 h-aged and d 12 h-aged Fe73Ga27 random polycrystals. e Figure of merit as a function of aging time for Fe81Ga19 random polycrystals. f Comparison of saturation magnetostriction among our optimally aged Fe–Ga random polycrystals, the quenched random polycrystals doped with a third element and the single crystals.

Recent advances on Nickel Nano-ferrite: A review on processing techniques, properties and diverse applications

Abstract: Ferrites belong to the wonder class of materials which are known for their wide application range. Among ferrites, spinel ferrites belong to the most promising soft magnetic materials with excellent properties like engineered band gap, high saturation magnetization, coercivity, and better thermal and electrical properties. Among spinel ferrites, Nickel ferrites: a soft, highly magnetic material that exhibit excellent electrical, magnetic, and optical characteristics. Nickel ferrites find their space in a variety of applications because of their unique properties when compared to other ferrite family members. These properties include high saturation magnetisation, less coercivity, high resistivity and permeability. In addition, nanometric Ni ferrites are unique in several properties with modified applications, such as high frequency applications, electronic devices with low loss, biomedical applications, and environmental remedial applications also. This review aim to explore possible synthesis routes, unique properties and diverse applications of Ni ferrite.

Cellular autofluorescence is magnetic field sensitive

Abstract: We demonstrate, by direct, single-cell imaging kinetic measurements, that endogenous autofluorescence in HeLa cells is sensitive to the application of external magnetic fields of 25 mT and less. We provide spectroscopic and mechanistic evidence that our findings can be explained in terms of magnetic field effects on photoinduced electron transfer reactions to flavins, through the radical pair mechanism. The observed magnetic field dependence is consistent with a triplet-born radical pair and a B1/2 value of 18.0 mT with a saturation value of 3.7%.

Pressure-Tuned Intralayer Exchange in Superlattice-Like MnBi2Te4/(Bi2Te3)n Topological Insulators.

Abstract: The magnetic structures of MnBi2Te4(Bi2Te3)n can be manipulated by tuning the interlayer coupling via the number of Bi2Te3 spacer layers n, while the intralayer ferromagnetic (FM) exchange coupling is considered too robust to control. By applying hydrostatic pressure up to 3.5 GPa, we discover opposite responses of magnetic properties for n = 1 and 2. MnBi4Te7 stays at A-type antiferromagnetic (AFM) phase with a decreasing Neel temperature and an increasing saturation field. In sharp contrast, MnBi6Te10 experiences a phase transition from A-type AFM to a quasi-two-dimensional FM state with a suppressed saturation field under pressure. First-principles calculations reveal the essential role of intralayer exchange coupling from lattice compression in determining these magnetic properties. Such magnetic phase transition is also observed in 20% Sb-doped MnBi6Te10 because of the in-plane lattice compression.

Highly Efficient 11.1-kW Wireless Power Transfer Utilizing Nanocrystalline Ribbon Cores

Abstract: Nanocrystalline alloys have been recently considered as an alternative to ferrite as the magnetic cores in inductive power transfer systems due to their superior properties such as higher saturation flux density and permeability. They are also less brittle, more stable to temperature variations, and have a higher thermal conductivity. To take advantage of these properties, a dedicated design approach is required, different from the one used for ferrite cores. In this article, special considerations and methods for the design of nanocrystalline ribbon cores are presented. An 11.1-kW pad is designed and compared with one with identical ferrite cores. Results show that IPT pads with nanocrystalline ribbon cores yield superior magnetic performance in terms of inductances and coupling factors. Higher efficiency and power density were also achieved with the proposed design. Furthermore, compared to ferrite-based pads, they showed lower leakage flux and a superior stability to temperature variations.

Laser Additive Manufacturing of Fe-Based Magnetic Amorphous Alloys

Abstract: Fe-based amorphous materials offer new opportunities for magnetic sensors, actuators, and magnetostrictive transducers due to their high saturation magnetostriction (λs = 20–40 ppm) and low coercive field compared with polycrystalline Fe-based alloys, which have high magnetostriction but large coercive fields and Co-based amorphous alloys with small magnetostriction (λs = −3 to −5 ppm) Additive layer manufacturing (ALM) offers a new fabrication technique for more complex net-shaping designs This paper reviews the two different ALM techniques that have been used to fabricate Fe-based amorphous magnetic materials, including the structural and magnetic properties Selective laser melting (SLM)—a powder-bed fusion technique—and laser-engineered net shaping (LENS)—a directed energy deposition method—have both been utilised to fabricate amorphous alloys, owing to their high availability and low cost within the literature Two different scanning strategies have been introduced by using the SLM technique The first strategy is a double-scanning strategy, which gives rise to maximum relative density of 96% and corresponding magnetic saturation of 122 T It also improved the glassy phase content by an order of magnitude of 47%, as well as improving magnetic properties (decreasing coercivity to 15915 A/m and increasing magnetic permeability to around 100 at 100 Hz) The second is a novel scanning strategy, which involves two-step melting: preliminary laser melting and short pulse amorphisation This increased the amorphous phase fraction to a value of up to 896%, and relative density up to 941%, and lowered coercivity to 238 A/m On the other hand, the LENS technique has not been utilised as much as SLM in the production of amorphous alloys owing to its lower geometric accuracy (025 mm) and lower surface quality, despite its benefits such as providing superior mechanical properties, controlled composition and microstructure As a result, it has been commonly used for large parts with low complexity and for repairing them, limiting the production of amorphous alloys because of the size limitation This paper provides a comprehensive review of these techniques for Fe-based amorphous magnetic materials

Improving the glass formation ability and magnetic properties by Nb in Fe-Si-B-P-Cu-Nb nanocrystalline alloys

Abstract: Fe-based nanocrystalline alloys with high saturation flux density (Bs) are highly desired for the miniaturization of electronic devices. However, the glass forming ability (GFA) and the temperature window of annealing processing of the high Fe content nanocrystalline alloys need to be improved to satisfy the industrial production. In this work, the influence of Nb on the GFA, crystalline behavior, soft magnetic properties of melt-spun Fe86.3-xSi1.3B8.9P3Cu0.5Nbx (0 ≤ x ≤ 4) alloys have been comprehensively investigated. It has been found that full amorphous structure can be obtained when the content of Nb is more than 3 at. %, and Nb may play a critical role in the optimization of crystalline processing. It has been also demonstrated that α-Fe (Si) grains were obviously refined by Nb so as to result in the decease of coercivity (Hc). In this work, Fe82.3Si1.3B8.9P3Cu0.5Nb4 ribbon exhibits an Hc of 4.2 A/m after relaxation, and a Bs of 1.54 T after annealed at 500℃, respectively, which are comparable to those of NANOPERM alloys.

Structural and magnetic evaluations of rare-earths (Tb, Pr, Ce, Gd, Y)-doped spinel ferrites for high frequency and switching applications

Abstract: NiZn nanoferrites doped with rare-earth cations having stoichiometric composition such as Ni0.5Zn0.5R0.02Fe1.98O4 (R = Tb, Pr, Ce, Gd, Y) were prepared by sol–gel technique. The same amount of Ni and Zn with constant ratio of different rare-earths ions were doped to investigate the variations in the properties. X-ray diffraction (XRD), Field emission electron microscope (FESEM), and vibrating sample magnetometer (VSM) were used to investigate the structure, morphology, and magnetic properties of rare-earth doped NiZn nanoferrites, respectively. X-ray density, bulk density, and porosity were also calculated. Phase, crystallite size, structure, d-spacing, lattice parameter, micro strain, and cell volume are also calculated. XRD patterns were refined using Rietveld refinement method. The refinement was implemented by materials analysis using diffraction (MAUD). Bertaut method was used to evaluate the bond lengths, site radii, and shared and unshared edges. Single phase for all rare-earth-doped NiZn nanoferrites was confirmed from refined patterns. GOF (goodness of fit) was in the range which verifies the good matching of patterns with the standard patterns. The micrographs depicted the different morphologies of the rare-earths-doped NiZn ferrites which confirms the behavior of rare-earth ions in NiZn ferrites. Saturation, initial permeability, anisotropy (Ka), coercivity, Y-K angles, remanence, and magnetic moments were measured from magnetic loops using VSM. Y- and Gd-doped NiZn nanoferrites demonstrated better magnetic properties as compared to other rare-earth-doped NiZn ferrites. Switching field distribution response from the prepared nanoferrites was also investigated. High-frequency response depicted the use of these nanoferrites in microwave frequency regions such as S, X, and Ku band because of their strong magnetization response.

An Overview of Saturable Inductors: Applications to Power Supplies

Abstract: This article presents an overview of saturable inductors that are intentionally saturated by the load current and their applications to power supplies. After introducing the fundamentals of magnetization and nonlinear inductance, three types of saturable inductors are differentiated. They are based on the way nonlinearity of the core material is used. The partial saturation, the saturation of swinging inductors and the full saturation. Subsequently, this article focuses on the application to power supplies: it identifies the main reasons for using saturable inductors, like improving the efficiency or reducing the size of the magnetic component by using stepped air-gaps or partial saturation and gives an overview on this topic and its main publications. Afterwards some concepts and circuits taking advantage of saturable inductors are presented in more detail, especially improving the light load efficiency of a point of load buck converter, ensuring zero voltage switching over a wide load range in a phase-shifted full bridge circuit, a nonlinear commutation circuit, and a passive and active power factor correction.

Topologically driven linear magnetoresistance in helimagnetic FeP

Abstract: The helimagnet FeP is part of a family of binary pnictide materials with the MnP-type structure, which share a nonsymmorphic crystal symmetry that preserves generic band structure characteristics through changes in elemental composition. It shows many similarities, including in its magnetic order, to isostructural CrAs and MnP, two compounds that are driven to superconductivity under applied pressure. Here we present a series of high magnetic field experiments on high-quality single crystals of FeP, showing that the resistance not only increases without saturation by up to several hundred times its zero-field value by 35 T, but that it also exhibits an anomalously linear field dependence over the entire range when the field is aligned precisely along the crystallographic c-axis. A close comparison of quantum oscillation frequencies to electronic structure calculations links this orientation to a semi-Dirac point in the band structure, which disperses linearly in a single direction in the plane perpendicular to field, a symmetry-protected feature of this entire material family. We show that the two striking features of magnetoresistance—large amplitude and linear field dependence—arise separately in this system, with the latter likely due to a combination of ordered magnetism and topological band structure.

Synthesis and structural, optical, and magnetic properties of Mn-doped CdS quantum dots prepared by chemical precipitation method

Abstract: Mn-doped CdS nanoparticles were successfully prepared by the chemical precipitation method. The effect of Mn doping on the structure, optical, and magnetic properties of the prepared samples was studied. Cubic CdS is indicated by XRD investigation and no change in CdS crystal structure was noted by Mn doping due to the low concentration of Mn doping. The morphology of the pure and 0.07% doped samples was investigated by a high-resolution transmission electron microscope (TEM). TEM images revealed mosaic-shaped grains with a size range of 7–8 nm. The thermal behavior and stability of the pure sample were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) in the argon atmosphere. The whole weight loss over the temperature range of 25–700 °C was about 17.4% which reveals the thermal stability of the prepared compound. The optical properties of the prepared samples were studied through diffuse reflection (DR). The transition energy increases only by the initial addition of Mn and then did not get affected by more Mn. The impact of doping on the energy bandgap, refractive index, and dielectric constant was discussed. Magnetic properties of Mn-doped CdS were investigated by a vibrating-sample magnetometer at room temperature. The results indicated an anti-ferromagnetic property with weak ferromagnetic behavior with no saturation.

Analytical Calculation of Active Magnetic Bearing Based on Distributed Magnetic Circuit Method

Abstract: To solve the problem that coupled magnetic flux and saturation of active magnetic bearing (AMB) cannot be taken into account in the traditional magnetic circuit calculation method together, this paper proposes a novel analytical calculation method based on distributed magnetic circuit method (DMCM). First, a magnetic circuit model with multiple magnetic circuits is built, we can obtain the initial flux density of each section by magnetic circuit calculation. Next, the magnetomotive force (MMF) of each magnetic circuit is calculated by the B-H curve of the ferromagnetic material. Then, the air-gap flux density under each magnetic pole center is obtained by further iterative calculations according to the magnetic potential error. On the basis, the flux density distribution along the air-gap circumference is obtained by one-dimensional (1D) relative permeance function, and thus the bearing capacity is derived and a loss calculation method is introduced. Finally, the finite element method (FEM) and experimental results show that the proposed method is feasible and effective.

Yb delafossites: Unique exchange frustration of 4 f spin-1/2 moments on a perfect triangular lattice

Abstract: While the Heisenberg model for magnetic Mott insulators on planar lattice structures is comparatively well understood in the case of transition metal ions, the intrinsic spin-orbit entanglement of $4f$ magnetic ions on such lattices shows fascinating new physics largely due to corresponding strong anisotropies both in their single-ion and their exchange properties. We show here that the Yb delafossites, containing perfect magnetic ${\mathrm{Yb}}^{3+}$ triangular lattice planes with pseudospin $s=\frac{1}{2}$ at low temperatures, are an ideal platform to study these phenomena. Competing frustrated interactions may lead to an absence of magnetic order associated to a gapless spin liquid ground state with a huge linear specific heat exceeding that of many heavy fermions, whereas the application of a magnetic field induces anisotropic magnetic order with successive transitions into different long-range ordered structures. In this comparative study, we discuss our experimental findings in terms of a unified crystal-field and exchange model. We combine electron paramagnetic resonance (EPR) experiments and results from neutron scattering with measurements of the magnetic susceptibility, isothermal magnetization up to full polarization, and specific heat to determine the relevant model parameters. The impact of the crystal field is discussed as well as the symmetry-compatible form of the exchange tensor, and we give explicit expressions for the anisotropic $g$ factor, the temperature dependence of the susceptibility, the exchange-narrowed EPR linewidth, and the saturation field.