Magnetically Soft Research Articles

Ferrites with a Minimized Secondary Electron Yield.

Ferrites are an essential material in modern industry due to their exceptional magnetic properties and high resistivity. Many applications of ferrites necessitate exposure to high energy electrons, particularly space science and particle accelerators, where charging, multipacting, and electron clouds (ECs) are major issues. ECs are of particular concern around the Ni/Zn soft ferrite kicker magnets as the large hadron collider (LHC) undergoes its high luminosity upgrade. Here, laser engineered surface structures (LESS) are used to reduce the secondary electron yield (SEY) of Ni/Zn ferrites from 2.1 to its experimentally determined minimum of 0.81, eliminating the ferrites ability to contribute to the formation of ECs. This demonstrates the applicability of LESS outside of metals and its broader applicability to reducing the SEY of technical materials.

Optimizing nanostructure and magnetic softness of Fe-Si-B-Cu nanocrystalline alloys via tailoring melt-spun structure by Al microalloying

Optimizing nanostructure and magnetic softness of Fe-Si-B-Cu nanocrystalline alloys via tailoring melt-spun structure by Al microalloying

Bilayer magnetic composite systems made of random anisotropy hexaferrite and soft metallic magnets for stealth technology

Abstract An experimental strong increase of the reflection loss (from 25 up to 35 dBs) and an extension of the absorption bandwidth up to 20% is measured in a set of novel functional bilayer systems. We focus our work on studying the samples in an anechoic chamber under far-field real radar conditions. Each layer consists of a composite material, typically a dielectric matrix filled with random anisotropy hexaferrite and soft metallic materials (powder or wires). Combining the two types of materials into a submillimetric bilayer structure has shown unprecedented improvements in microwave absorption capacities compared to the former absorption of each layer. The capacity to improve the shielding behavior is strongly related to each layer’s permittivity, permeability, and thickness leading, therefore, to a strong control over the design of novel materials for stealth applications.

Severe plastic deformation of Mn-Al permanent magnets

Manganese-aluminum permanent magnets are promising candidates to fill the cost and performance gap between lower-performance bonded ferrites and high-performance magnets based on rare-earth elements. This is due to the favorable combination of saturation magnetization and magnetocrystalline anisotropy in the Mn-Al τ phase combined with low raw material cost. However, the τ phase is metastable and prone to decomposition at high temperatures, making processing by conventional milling and sintering difficult. Severe plastic deformation (SPD) is an alternative processing route to control the microstructure of a material by applying very high amounts of strain. In this study, equal-channel angular extrusion (ECAE) and high-speed high-pressure torsion (HS-HPT) were both tested as SPD processing routes. ECAE improved magnetic energy product, (BH)max, by 220% by refining the grain size and imparting a high density of dislocations. HS-HPT enabled a rapid phase transformation from the high-temperature ε phase to the τ phase but lowered Hci, making it better suited to soft magnet processing.

Magnetic Sensor Using a Microfabricated Soft Magnet Resonator With Active Q-Factor Enhancement

Magnetic Sensor Using a Microfabricated Soft Magnet Resonator With Active Q-Factor Enhancement

Effect of multivalent ion doping on magnetic, electrical, and dielectric properties of nickel ferrite nanoparticles

The nanoscale spinel structured ferrites co-doped with multi-valence ions are of great interest and proving to be promising for numerous applications. In light of this, herein we report tetravalent titanium ions (Ti4+) and divalent zinc ions (Zn2+) co-doped nickel ferrites with generic formula of NiFe2 − 2xTixZnxO4 (x = 0.00 ≤ x ≤ 0.20 in step of 0.05). The sol gel self combustion method in assistance with citric acid as fuel was employed to prepare the samples. The X-ray diffraction (XRD) analysis with Rietveld refinement was performed to confirm the single-phase cubic spinel structure. The sphere type grain morphology of the samples was revealed by SEM images. The compositional studies carried out by EDAX showed desired formation of the composition with absence of impurities in the samples. The characteristics bands belonging to the spinel ferrites were appeared in IR spectra confirming the successive sample forming. The different surface parameters including surface area and pore volume was estimated using Brunauer-Emmett-Teller (BET) analysis. The low coercive nature with soft magnetism was observed with the co-doping as revealed by M-H plots. The electric and dielectric parameters showed decrementing behaviour with increment in Ti4+-Zn2+ co-doping. This study outcome signifies that the Ti4+-Zn2+ co-doping in nickel ferrites could be a prominent for many nanoelectronics applications.

Electrodeposited NiFeCo + Tb and Dy for Enhanced Magnetostrictive Properties and Soft Magnetism

Magnetostrictive thin films have numerous applications in communications, sensors, and microelectronic devices. Such devices usually require magnetostrictive thin films with large magnetostriction and soft magnetic properties. Nickel-Iron-Cobalt alloys can be easily fabricated as thin films in addition to having excellent soft magnetic properties. Their main drawback for these sensing applications is that they have very low magnetostriction. On the other hand, Iron-Rare Earth (RE) alloys such as Fe-Tb-Dy or Fe-Ga have large magnetostriction at the cost of some soft magnetic properties. We report the development of Nickel-Iron-Cobalt thin films with incorporated rare earth elements with large magnetostriction and soft magnetic properties. The combination of these properties makes these NiFeCo thin films with added Tb and Dy excellent candidates for developing resonant frequency communication devices.

Microstructural and Magnetic Characteristics of High-Entropy FeCoNiMnTi Alloy Produced via Mechanical Alloying

In the current study, X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometer techniques were used to examine the impact of milling time on the microstructural and magnetic characteristics of Fe30Co20Ni20Mn20Ti10 (at%) produced via mechanical alloying. Results demonstrate that phase change is dependent on up to 30 h of milling. In terms of the hcp-Fe2Ti intermetallic and the BCC-FeCoNiMnTi supersaturated solid solution, the system maintains its two-phase structure at higher times. Additionally, the final average crystallite size was estimated to be approximately 10 nm, and the lattice strain was found to be between 0.95 and 1.15 %. As a function of milling time, the magnetic properties are discussed with the microstructural and crystallographic alterations. The collected powder after 100 h of milling has an Ms value of 28 emu/g and a Hc value of 25 Am−1, which is consistent with exceptional soft magnetics. This is essentially due to the Fe2Ti intermetallic and the BCC-Fe-based solid solution production, together with the refinement of the crystallite size. Furthermore, the presence of paramagnetic Ti atoms in solid solution and the development of high densities of defects and interfaces have been connected to the low value of Ms.

New solid solutions with the R-type hexaferrite structure, BaFe4-xMxM’2O11 (M = In, Sc; M’ = Ti, Sn)

Hexaferrites are a family of complex iron oxides with hexagonal structures. Novel compositions with the R-type hexaferrite structure, BaFe4-xMxM’2O11 (M = In, Sc; M’ = Ti, Sn; x = 0.0–1.8), are synthesized and characterized. Structural analyses using powder neutron diffraction reveal that trivalent iron cations are distributed among all the available M sites (octahedral and trigonal bipyramidal sites), with site preference varying with the composition. Ferrimagnetic behavior is observed for all the compounds, and the observed magnetic hysteresis loop indicates that the compounds are soft magnets. The color of the new solid solution can be tuned from dark reddish brown to reddish-orange and yellowish-orange as In or Sc substitutions increase. The origin of colors in these ferrite-based solid solutions results from the combination of ligand-to-metal charge transfer and electron-pair transitions across the face-shared octahedra, as seen in the hematite (Fe2O3). Reducing Fe content in the parent compound improves the diffuse reflectance in the near-infrared range, suggesting potential applications as cool pigments.

Nanostructure-induced functional combination of vanishing magnetostriction and magnetic softness in ferromagnetic (GaNi)xCoCrFe (x = 0.4–1.6) high-entropy alloys

Searching for high-entropy alloys with functional properties that emerge from their multi-scale structure, we have investigated the (GaNi)xCoCrFe (x = 0.4–1.6) system. We have characterized structure, microstructure, nanostructure and chemical composition of the individual phases in the multi-phase alloys and determined their magnetic, magnetostrictive and electrical properties. We found that the alloys are ferromagnetic and exhibit functional combination of magnetic softness and vanishing magnetostriction, classifying them as energy-efficient “supersilent” materials (inaudible to a human ear) for alternating-current (AC) electromagnetic applications in the audio-frequency range. The alloys develop a two-phase structure, a face-centered cubic (fcc) and a body-centered cubic (bcc), where the fcc phase fraction decreases, while the bcc fraction increases with the increasing (GaNi)x content. Ferromagnetism of the alloys originates from the highly nanostructured bcc phase, with the ferromagnetic Curie temperatures in the range TC = 750–700 K, depending on x. The fcc phase is not nanostructured and is paramagnetic at room temperature, but undergoes a spin glass transition at Tf≈6.4 K. The magnetic softness and vanishing magnetostriction of the alloys are both nanomagnetic phenomena. The magnetic-softness and magnetostriction parameters of the x = 1.3 and 1.6 alloys make them relevant for supersilent AC applications at low frequencies.

Finite element analysis and design of a magnetostrictive material based vibration energy harvester with a magnetic flux path

Abstract This work presents the development of a nonlinear 2D finite element (FE) framework for magnetostrictive material based energy harvesters of beam geometry. The FE model is developed in COMSOL Multiphysics and compared with existing literature for validation. The FE model is subsequently used to study the effect of a closed magnetic flux path, consisting of ferromagnetic components, on the harvester output. Specifically, the voltage output is obtained by performing simulations on unimorph type harvester devices with and without a closed magnetic flux path, both operating at the same natural frequency and volume of the magnetostrictive material Galfenol. The harvester design considered here consists of a magnetostrictive layer (Galfenol) bonded to a steel substrate layer, a tip mass, a pick-up coil and a magnetic flux path consisting of soft iron core and NdFeB permanent magnets. Our results demonstrate a voltage gain of around 70% for the closed flux path design. Furthermore, a proof of concept prototype of the modified flux path design is developed, tested under impulse loading, and the voltage, power output are compared with FE simulation results for validation. The simulation results match well with experimental observations at two operating frequencies for the flux path design.

A General Model for the Ductility of Intermetallics Applied to Fe-Co Alloys

The mechanical properties, specifically ductility, of high performing soft magnets such as Fe-Co alloys are a limiting factor to their broader use in a number of systems. The understanding of the mechanical robustness in these materials is currently insufficient to be able to support the growing interest in applications such as magnetic shielding or electric motors. Fe-Co alloys provide the highest commercially available magnetic saturation and high magnetic permeability but have very poor ductility. The addition of vanadium to these alloys has allowed for significant commercialization and some ductility improvements, but the fundamental reasons for the observed improvements are not well understood. In most published work on mechanical properties in these alloys, the precise chemistry of the alloys investigated, often a critical aspect of intermetallics, is not reported or controlled and thermal history is unclear. This work creates a ductility model that is sensitive to changes in chemistry and can predict relative strain to failure as well as brittle fracture mode for intermetallics and is applied to Fe-Co alloys. Through the application of density functional theory (DFT), this model identifies defect stabilities, anti-phase boundary (APB) energies, the energy necessary to cross-slip, and cleavage energies and combines them through energetic competition to determine a relative failure strain. The model correctly predicts ductility improvements with the addition of vanadium as well as the transition from intergranular to transgranular cleavage, though more precise experiments are necessary to appropriately validate the various improvements observed.

Correlation of microstructure and magnetic softness of Si-microalloying FeNiBCuSi nanocrystalline alloy revealed by nanoindentation

Abstract Compared to the commercial soft-magnetic alloys, the high saturation magnetic flux density (B s) and low coercivity (H c) of post-developed novel nanocrystalline alloys tend to realize the miniaturization and lightweight of electronic products, thus attracting great attention. In this work, we designed a new FeNiBCuSi formulation with a novel atomic ratio, and the microstructure evolution and magnetic softness were investigated. Microstructure analysis revealed that the amount of Si prompted the differential chemical fluctuations of Cu element, favoring the different nucleation and growth processes of α-Fe nanocrystals. Furthermore, microstructural defects associated with chemical heterogeneities were unveiled using the Maxwell–Voigt model with two Kelvin units and one Maxwell unit based on creeping analysis by nanoindentation. The defect, with a long relaxation time in relaxation spectra, was more likely to induce the formation of crystal nuclei that ultimately evolved into the α-Fe nanocrystals. As a result, Fe84Ni2B12.5Cu1Si0.5 alloy with refined uniform nanocrystalline microstructure exhibited excellent magnetic softness, including a high B s of 1.79 T and very low H c of 2.8 A/m. Our finding offers new insight into the influence of activated defects associated with chemical heterogeneities on the microstructures of nanocrystalline alloy with excellent magnetic softness.

Composition and microstructure engineering of Fe–Si–Co soft magnetic alloys with enhanced performance

The growing demand for high-efficiency and low-loss energy conversion and transportation techniques urges the development of advanced Fe–Si based soft magnet alloys. Simultaneous achievement of low coercivity (Hc) and large saturation magnetization (Ms) however, remains challenging. In this study, soft magnetic alloys with the composition Fe82–xSi18Cox (x = 0 at.%, 4 at.%, 8 at.%, 12 at.%, 16 at.%, and 20 at.%) have been designed followed by microstructural tuning. The Co incorporation results in initially decreased Hc followed by increment due to reduced magnetocrystalline anisotropy and increased saturation magnetostriction from negative to positive values of the alloys. Meanwhile, the Ms raises with subsequent reduction, which origins from competitive mechanisms of increased average moment of Fe atoms and decreased average moment of Co atoms according to first principles calculations. Microstructural evolution during annealing of the Fe70Si18Co12 with synergistically optimized Hc and Ms has been revealed that after elevated-temperature annealing, the DO3 phase is predominately transformed from the B2 phase accompanied by an increase in the degree of ordering. The growth of the DO3 phase deteriorates the Hc due to the aggravating pinning effect on the domain wall movement, which arises from the inhomogeneous magnetization distribution caused by increasing antiphase boundaries.

Research on Magnetic-Thermal Coupling of High-Permeability Soft Magnets in SynRMs

Research on Magnetic-Thermal Coupling of High-Permeability Soft Magnets in SynRMs

Untethered soft magnetic pump for microfluidics-based Marangoni surfer

Microfluidics has enabled the miniaturization of fluidic systems for various biomedical and industrial applications, including small-scale robotic propulsion. One mechanism for generating propulsive force through microfluidics is by exploiting the solutal Marangoni effect via releasing surfactant on the air-water interface. Surfactants locally reduce the surface tension, which leads to a surface stress that can propel the floating robot, called Marangoni surfer. However, so far the release of the surfactant is not controllable. In this study, we combine microfluidics-based Marangoni propulsion with a novel untethered magnetic pumping mechanism to enhance its controllability. The proposed magnetic micropump capitalizes on the interaction force between two soft magnets, which can generate a pumping force of 4.64 mN to actuate a membrane, and achieve a deformation of 450 μm. Net flow is achieved using a nozzle/diffuser flow rectifier whose efficacy as a function of the channel geometry is numerically studied. We investigate the flow rate of the pump with regard to the actuation frequency. Finally, we demonstrate its ability to control the motion of the Marangoni surfer.

Enhanced dipole-interaction in Nd-Dy-Fe-Co-B/Fe composite thick stacked trilayer

It is crucial to better understand the magnetization reversal process between soft and hard magnets and to achieve a high maximum energy product in thick composite multilayers. In this study, we find that the exchange interactions dominate in soft–hard-magnetic composite bilayers, while dipole interactions are predominant in soft–hard-magnetic composite trilayers. Based on the first-order reversal curve, magnetization reversal models are developed for both the thick composite bilayer and trilayer. Dipole interactions play an important role in the long range, resulting in higher coercivity and remanence in the thick trilayer. A multilayer in a stacked trilayer structure is achieved, which is composed of thick films with a perpendicular magnetic anisotropy at a thickness of up to 16 μm. The enhanced dipole interactions lead to a remanent polarization of 1 T and a maximum energy product of 22.5 MGOe. This work contributes to the preparation of thick films with a high maximum energy product for applications in magnetic microelectromechanical systems.

Magnetic properties of hard-soft MnBi/FeNi@C exchange coupled nanostructures via cryo-milling

The extremely important permanent magnets encounter uncertainty and cost variations due to utilization of rare earths as prime components. Hence, the exchange coupled magnets comprised of hard and soft magnets in different proportions are explored to optimize the magnetic properties and cost. In this line, we prepared exchange coupled magnets of MnBi with FeNi@C nanoparticles (varying compositions = 10, 15 and 20 wt %) via cryogenic ball milling route. Out of these, the nanocomposite with MnBi and 15 wt% FeNi@C provided a coercivity value of 7.9 kOe with saturation magnetization and remanance values of 63 and 38 emu/g respectively. This exchange coupled magnet shown improvement in the MS, HC and Mr values by 53, 18 and 90 % respectively as compared to MnBi alone. The carbon layer over FeNi@C phase (MS = 147 emu/g) as well as cryomilling facilitated the formation of its exchange coupled magnet with MnBi.

Magnetic interaction in Sr0.7La0.3Fe11.75Co0.25O19–CoFe2O4 composite system: observation, evidence, and influence

(100-x) Sr0.7La0.3Fe11.75Co0.25O19–(x) CoFe2O4 composites were synthesized by the one pot sol–gel auto-combustion method. The individual phase purity, morphology, and magnetic hysteresis loop of the composite magnet were analyzed by x-ray powder diffraction, field emission scanning electron microscopy and vibrating sample magnetometer, respectively. The apparent observation of the room temperature hysteresis loop indicates the existence of interfacial exchange interactions. Nevertheless, saturation magnetization (Ms ) follows the trend of Vegard’s law. The nature of magnetic interaction and its dependency on the amount of each phase were analyzed by employing the Thamm–Hesse plot. The critical size of the soft phase particle did not corroborate with the results of ΔM vs H plot. However, this synthesis method is found to be successful in obtaining single-step magnetization reversal in hard–soft composite magnets. The deviation from ideal non-interacting Stoner–Wohlfarth particles puts the single hard phase into the limelight. The (BH)max in the range of 1.07–0.98 MGOe has been obtained for the synthesized composite magnet.

Ultrathin Ternary FeCoNi Alloy Nanoarrays in BaTiO3 Matrix for Room-Temperature Multiferroic and Hyperbolic Metamaterial.

Multifunctional vertically aligned nanocomposite (VAN) thin films exhibit considerable potential in diverse fields. Here, a BaTiO3-FeCoNi alloy (BTO-FCN) system featuring an ultrathin ternary FCN alloy nanopillar array embedded in the BTO matrix has been developed with tailorable nanopillar size and interpillar distance. The magnetic alloy nanopillars combined with a ferroelectric oxide matrix present intriguing multifunctionality and coupling properties. The room-temperature magnetic response proves the soft magnet nature of the BTO-FCN films with magnetic anisotropy has been demonstrated. Furthermore, the anisotropic nature of the dielectric-metal alloy VAN renders it an ideal candidate for hyperbolic metamaterial (HMM), and the epsilon-near-zero (ENZ) wavelength, where the real part of permittivity (ε') turns to negative, can be tailored from ∼700 nm to ∼1050 nm. Lastly, room-temperature multiferroicity has been demonstrated via interfacial coupling between the magnetic nanopillars and ferroelectric matrix.