Soft Magnetic Behavior Research Articles

Effect of Al/Cr ratio on structure, magnetism, and corrosion resistance of FeCoNiCr1-xAlx high entropy alloys

This study investigates the microstructure, magnetic properties, and corrosion resistance of FeCoNiCr1-xAlx (x=0, 0.25, 0.5, 0.75, 1) high-entropy alloys using the combination of experimental methods and first-principles calculations. XRD results reveal the FCC-BCC phase transition as x increases, and FeCoNiCr1-xAlx exhibits a noticeable dual-phase structure when x=0.75. The partial segregation between Ni and Al elements is indicated by SEM-EDS observations. The magnetism of both FCC and BCC phases become strong with increasing x, and the BCC phase consistently exhibiting higher magnetism than the FCC phase. Potentiodynamic polarization curves show that Al0.25 has the highest corrosion potential and the lowest corrosion current density. Under open circuit potential conditions, due to the difference between the corrosion potential and the open circuit potential, the electrochemical impedance spectroscopy measurements indicate that the corrosion resistance of the alloys follows the order: Al0 > Al0.5 > Al0.75 > Al0.25 > Al1. Considering both the soft magnetic behavior and corrosion resistance, Al0.75 is a optimal choice. These findings provide valuable insights for developing magnetic high-entropy alloy materials with superior corrosion resistance.

Influence of P and C co-alloying on soft magnetic properties and crystallization behavior of FeSiBPCCu nanocrystalline alloys

In this study, multicomponent synergistic effects were adopted to enhance the glass-forming ability (GFA), processing window (PW), thermal stability, and soft magnetic properties (SMPs) of FeCuSiB nanocrystalline alloys (NAs) with high Fe and Cu contents via P and C co-alloying. The co-addition of P and C is beneficial for enhancing the GFA, expanding the PW, and increasing the crystallization resistance of the compound phases in present FeCuSiBPC alloys. Consequently, the Fe81.5Cu1.7Si3.8B9P3C1 alloy exhibited a large optimum TA window of up to 100 °C and a large tA window of 40 min for nanocrystallization. Crystallization kinetic analysis showed that the co-addition of P and C led to a high-frequency factor (v) in the precipitation of α-Fe crystals, which was related to the high nanocrystal density (Nd) of α-Fe. This result may be attributed to the nucleation of α-Fe by Cu and CuP clusters. Additionally, the co-addition of P and C increased the growth active energy (Ep) of the α-Fe crystals because of their larger atomic diffusion resistance. The high Nd and Ep values led to the formation of fine nanostructures and excellent SMPs in FeCuSiBPC alloys. Therefore, the Fe81.5Cu1.7Si3.8B9P3C1 NA obtained by annealing at 420 °C for 30 min exhibited excellent SMPs with a Bs of up to 1.78 T, a low Hc of 7.5 A/m, and a high μe of 9863 (@1kHz). This study provides technical and theoretical guidance for optimizing the composition and processability of NAs with high Fe and Cu contents, paving the way for mass production of high-performance soft magnetic NAs.

Sr4Os3O12 – A Layered Osmate(V,VI) that is Magnetic Close to Room Temperature

AbstractBlack crystals of the mixed‐valence osmate(V,VI) Sr4Os3O12 were grown via a gas phase reaction in an evacuated silica tube. The material is attracted to a permanent magnet at room temperature (295±5 K) but loses this property when heated or cooled. In this temperature interval, soft magnetic behavior with vanishing coercivity is observed, but the saturation magnetization is only 0.05 μB per formula unit. Resistivity measurements show that Sr4Os3O12 is a semiconductor with a small band gap of about 0.26 eV at room temperature. X‐ray diffraction on a single‐crystal revealed a rhombohedral structure with the space group R m and lattice parameters ar=554.64(2) pm and cr=2700.1(1) pm at 300(1) K. The compound crystallizes in the La4Ti3O12 structure type and is isostructural to Sr4CoRe2O12. The structure is a rhombohedral stack of layered blocks, each of which can be considered as a section of three layers of the cubic perovskite structure cut perpendicular to one of its threefold axes. The Os–O−Os bond angle of about 175° favors superexchange that leads to antiferromagnetic coupling between the osmium atoms with 5d3 and 5d2 configurations. Sr4Os3O12 exhibits strong lattice dynamics. One aspect is the antiferro‐rotative lattice modes of the corner‐sharing [OsO6] octahedra, which freeze upon cooling. At 100 K, an ordered, yet twinned triclinic superstructure is formed. Strong spin‐orbit coupling and other effects cause deformations of the [OsO6] octahedra that differ significantly at 300 K and 100 K, suggesting a change in the electronic configuration. Competing ground states could also explain the temperature‐dependent band gap and the magnetic fluctuations manifested in the magnetization peak at room temperature.

Influence of Mo dopants on the vibrational, emission, dielectric, electrical, and magnetic properties of combustion synthesized ZnFe2O4 nanostructures for optoelectronic and spintronic applications

This report investigates the dielectric and magnetic behavior of Molybdenum (Mo)-incorporated ZnFe2O4 prepared via combustion route with different dopant concentrations (0.0, 0.1, 0.25, 0.5, 0.75, and 1.0 wt.%). XRD patterns reveal the cubic spinel structures with a slight increase in lattice constant while replacing Mo at Fe sites. Mo doped induced lattice constant increase from 8.444 to 8.469 Å coupled with a significant increase in density. Raman spectroscopy reveals a decrement in the peak broadening of the A1g mode at higher Mo concentrations, indicating longer phonon lifetimes. Scanning electron microscopy (SEM) and EDX analysis confirm the agglomerated pseudo-spherical structures with uniform elemental distribution over the surface. Further, the dielectric constant values exhibit a slightly decreasing trend with increasing frequency, and the mechanisms were discussed based on the intrinsic polarization due to the charge imbalance between Fe3+ and Fe2+ states. Further, the magnetic measurements confirm the soft magnetic behavior with saturation magnetization ranging from 13.72 to 14.61 emu/g and coercivity between 07 (Oe) to 44 (Oe). The overall findings demonstrate that Mo doping in ZnFe₂O₄ significantly modifies the dielectric and magnetic properties, making it a promising material for various technological applications.

Cr–Sc co-substituted nickel-cobalt nanospinel ferrites: An investigation of their structural, magnetic properties and hyperfine interactions

The chromium and scandium co-substituted nickel-cobalt nanospinel ferrites (NSFs) having general formula of Co0.5Ni0.5ScxCrxFe2-2xO4 (CoNiScCr) (x ≤ 0.10) have been fabricated through the sol-gel route and citric acid as fuel and characterized by X-ray diffractometry (XRD), 57Fe Mössbauer spectroscopy, vibrating sample magnetometry (VSM), and finally by scanning and transmission electron microscopy techniques (SEM and TEM, respectively). The crystallite size (Dmax) values of the products were estimated to lay between 31 and 46 nm, which was calculated by the Scherrer formula. It was observed that the doping ions’ concentration did not have a linear impact on the expansion of the lattice constant. SEM and TEM present the cubic shape of CoNiScCr NSFs. All ratios demonstrate highly agglomerated cubic particles with diverse sizes. Both XRD and EDX (Energy Dispersive X-ray Spectroscopy) analyses confirmed the absence of any impurity/phases. Through an analysis of hysteresis loops at 300 (RT = room temperature) and 20 K, along with a probe of temperature-induced alteration in magnetization M, the magnetic properties of CoNiScCr (x ≤ 0.10) NSFs have been thoroughly investigated. Notably, all products exhibited complementary soft and hard magnetic behaviors at RT and 20 K, respectively. At 20 K, the observation of squareness ratio values surpassing 0.5 exhibits a single-domain behavior at this specific temperature. Magnetic parameters, in general, exhibit fluctuations with increasing doping content. Across the entire range of materials studied, a notable trend emerges as the temperature decreases, the magnetization in the zero field cooling curves shows a non-linear decrease, eventually stabilizing in the field cooling branches. The findings suggest that the inclusion of Sc3+/Cr3+ dopants can be utilized to manipulate and achieve desired magnetic properties in Co–Ni ferrites. The spectra of Mössbauer analysis, which was utilized to establish the distribution of cations, presented four magnetic sextets for all samples. Doped ions are substituted with Fe3+ ions at the B site.

Electrochemical deposition of cobalt phosphorus for hard magnetic micro devices and the impact on magnetic anisotropy

When fabricating magnetic components for micro-electro-mechanical systems, the intrinsic material properties as well as the magnetic anisotropy of the deposited material and the fabricated devices must be adjusted to the application. This work focuses on electrochemically deposited cobalt phosphorus layers from a sulfate-based electrolyte to be used as hard magnetic scales in position measurement systems. In preliminary tests round discs (5 mm diameter, 20 or 10 μm height) were fabricated, showing the influence of three process parameters (current density, pH-value and temperature) on the chemical composition and the magnetic behavior of the deposited cobalt phosphorus. Hereby deposition parameters to produce hard magnetic cobalt phosphorus are defined. Deposits with up to 6 wt.-% phosphorus show hard magnetic behavior, whereas deposits with more than 6 wt.-% show soft magnetic behavior. This is correlated with a transition from crystalline to amorphous structures. In further investigations arrays of micro scales (40 μm width, 10 μm height) were fabricated to show the influence of direct current and pulsed current on the properties of the deposits. Pulsed current increases coercive field strength by about 40 %, resulting in maximum values of 23 kA/m (in-plane) and 14 kA/m (out-of-plane). Remanence increases by about 30 %, resulting in maximum values of 0.40 T (in-plane) and 0.2 T (out-of-plane). Pulse plating changes preferred orientation from (110) to (100) and slightly increases grain size by about 20 %, resulting in an average grain size of 25 nm.

Integrative approach to enhance the soft magnetic properties of Co35Cr5Fe10Ni30Ti20-xAlx (x= 10, 15, 20) high entropy alloys

High Entropy Alloys (HEAs) are advanced materials having multi-functional properties. These materials have the potential to overcome the shortcomings of conventional soft magnetic alloys. In this study, an integrative approach is adopted to enhance the magnetic and electrical properties of CoCrFeNiTi-based HEA by the addition of Al in different content for Ti and annealing for different temperatures and durations. Firstly, Co35Cr5Fe10Ni30Ti20-xAlx (x= 10, 15, 20) HEAs were synthesized through mechanical alloying and investigated for phase formation and magnetic properties. Major fcc with minor bcc and intermetallic R phase has formed for Co35Cr5Fe10Ni30Ti10Al10 and Co35Cr5Fe10Ni30Ti5Al15 HEAs. However, the mixture of fcc and bcc phase with a minor fraction of σ phase has been found for Co35Cr5Fe10Ni30Al20 HEA. The value of Ms is slightly decreased for Co35Cr5Fe10Ni30Ti5Al15 HEA as compared to Co35Cr5Fe10Ni30Ti10Al10 HEA, but for Co35Cr5Fe10Ni30Al20 HEA, the value of Ms has drastically decreased when Ti completely removed for Al. Among these three synthesized HEAs, the highest value of Ms is found for Co35Cr5Fe10Ni30Ti10Al10 HEA (Ms=78 emu/g). Further, we investigated the effect of annealing at different temperatures for 2 h on phase evolution, microstructure, and their correlation with magnetic properties of Co35Cr5Fe10Ni30Ti10Al10 HEA. Among annealed HEA, 700°C annealed Co35Cr5Fe10Ni30Ti10Al10 HEA has high Ms (104 emu/g), and the value of Hc was found to be 29 Oe. The long-duration annealing is also performed at 700°C for 10 h to improve the magnetic properties of the as-synthesized Co35Cr5Fe10Ni30Ti10Al10 HEA and found good soft magnetic behaviour (Ms=103.5 emu/g and Hc=13 Oe). Moreover, the electrical resistivity of the long-duration annealed Co35Cr5Fe10Ni30Ti10Al10 HEA is also recorded in the temperature range 2–350 K, and the value of electrical resistivity at 2 K and 300 K is found to be 180.2 ×102 µΩ.cm and 200.80 ×102 µΩ.cm, respectively. The found value of electrical resistivity is the highest value of resistivity reported so far in the case of soft magnetic HEA.

Facile sol–gel synthesis of trivalent Al3+-Gd3+ ions co-doped nanoscale cobalt spinel ferrite for magneto-electronic applications

The magnetic spinel ferrites nanomaterials simultaneously doped with multivalent cations have gained a lot of interest from many researchers during the last decade. Also, the doping of trivalent rare-earth ions in spinel ferrites is promising for many technological applications. Considering these facts, in this work we investigated the trivalent Al3+-Gd3+ ions co-doped cobalt ferrite nanoparticles with nominal composition as CoFe2-2xAlxGdxO4 (x = 0.00, 0.03, 0.05, 0.07, 0.10). The sol–gel auto ignition route assisted by citric acid as a chelating agent was utilized to synthesize the series of nanoparticles. The Rietveld refined X-ray diffraction (XRD) patterns were analyzed to ensure the single-phase formation of nanoparticles with spinel cubic structure. The spherical-shaped grain morphology of the nanoparticles was indicated by scanning electron microscopy (SEM) images. The elemental analysis obtained by energy dispersive X-ray analysis (EDAX) revealed stoichiometric formation of the samples along with high purity. The two prominent frequency modes analogous to the spinel ferrite structure were noted in the infrared spectra assuring the successful formation of all the samples. The soft magnetic behaviour with a lower coercivity of the prepared nanoparticles was confirmed by the vibrating sample magnetometer (VSM) technique. The DC electrical resistivity plots indicated that resistivity decreases with an increase in Al3+-Gd3+ co-doping. The dielectric studies of all the samples showed increasing behaviour with an increase in Al3+-Gd3+ co-doping. All the results suggest that the Al3+-Gd3+ co-doped cobalt ferrite nanoparticles can be useful for real-world applications, specifically in nanoelectronics devices.

Investigation of structural, elastic, thermal, magnetic, optical, and photocatalytic properties of nanosized Mg-Mn-Li ferrites

Nanoferrites of (Mn1-xMgx)0.8Li0.1Fe2.1O4 (x: 0–1.0, step 0.2) were synthesized by the sol–gel autocombustion method. The structural properties of the samples were characterized by X-ray diffraction, particle size analysis, transmission electron microscopy, and Fourier transform infrared spectroscopy. The X-ray diffraction patterns for the samples establish the nanoscale (38–54 nm) pure-phase spinel cubic structure (Fd-3̅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{3}$$\\end{document}m). Also, the particle size analysis results demonstrate the narrow distribution of their particle sizes, which range from 10 to 33 nm. The impact of Mg2+ ion concentration on the thermal, elastic, magnetic, and optical properties of these samples was studied. The saturation magnetization decreases from 56.9 to 31.1 emu/g, and the coercivity increases from 65.8 to 106.8G with the addition of Mg2+ ions, showing thin S-shaped hysteresis loops revealing the samples’ soft magnetic behavior. Thermal results indicate that these samples are interesting candidates for thermoelectric applications due to their noticeably lower thermal conductivity, which ranges from 0.3572 to 0.5881 W/mK. The optical band gap values determined by using ultraviolet-visible diffuse reflectance spectroscopy range from 5.11 to 5.25 eV, where quantum confinement for crystallite size triggers a larger band gap. As the concentration of Mg2+ ions increases, their ability to degrade methyl green dye under ultraviolet radiation for 100 min rises from 13.6 to 61.1% with the addition of H2O2, an indication of their photocatalytic activity. Moreover, the optimum ferrite sample, Mn0.4Mg0.4Li0.1Fe2.1O4, maintained its photocatalytic efficiency for at least six reaction cycles.Graphical The composition dependence of (a) the mexp and mth and (b) the ao and ath for the (Mn1−x Mgx)0.8Li0.1Fe2.1O4 nanosamples.

Structural, Mössbauer and magnetic study of (Mn0.2Co0.2Ni0.2Cu0.2X0.2)Fe2O4 (X=Fe, Mg) spinel high-entropy oxides fabricated via reactive flash sintering

Herein, it is reported the concomitant synthesis and sintering in a single step of (Mn0.2Co0.2Ni0.2Cu0.2X0.2)Fe2O4 (X=Fe, Mg), a spinel-structured high-entropy oxides, by the reactive flash sintering technique. A single phase, identified with a spinel crystal structure Fd3̅m, was obtained in just 30 min at a furnace temperature of 1173 K. The structural and magnetic properties of the prepared compounds were assessed by the combined use of various techniques, aiming to understand the correlations between functional properties and crystal structure. Characteristic features of the Mössbauer spectra prove the existence of different nonequivalent Fe environments . Both compositions display soft magnetic behavior, characterized by low coercive fields and saturation magnetization reached at low fields. Thus, the substitution of nonmagnetic Mg2+ for magnetic Fe2+ results in a decrease in magnetic parameters due to the weakening of the super-exchange interaction among the magnetic moments.

Relating laser powder bed fusion process parameters to (micro)structure and to soft magnetic behaviour in a Fe-based bulk metallic glass

This work aims to establish fundamental processing-(micro)structure-property links in a commercial Fe-based Kuamet6B2 bulk metallic glass (BMG) processed by laser powder bed fusion (LPBF). With that purpose, amorphous powders were processed using a pulsed-wave system and a simple meander strategy. The laser power, the scan speed, and the hatch distance were varied over wide intervals within the conduction regime. The processability window leading to samples with good dimensional accuracy and mechanical stability was determined. Within this window, the manufactured samples were crystalline/amorphous composites and the crystalline regions were formed by equiaxed ultrafine and nanograins with random orientations. Processing parameters yielding the densest prints caused severe crystallization while, conversely, parameter sets allowing the material to retain a high amorphous fraction led to significant lack-of-fusion defects and residual cracking along directions perpendicular to crystalline/amorphous interfaces. Comparatively, for a fixed hatch distance, the scanning speed had a stronger effect than the laser power in the resulting amorphous fraction due to its stronger influence on the melt pool size and, in turn, on the corresponding HAZ volume. The saturation magnetization and the coercive field were inversely related to the amorphous fraction. This work allows to derive fundamental guidelines for the successful additive manufacturing of soft magnetic Fe-based bulk metallic glasses (BMGs) by laser powder bed fusion (LPBF).

Magnetic properties and coupled spin‒phonon behavior of M‒type Sr1-xSmxFe12O19 (0 ≤ x ≤ 0.15) nanoparticles

We thoroughly investigated the effects of Sm³⁺ doping on the magnetic, structural, hyperfine, and vibrational properties of Sr1-xSmxFe12O19 (0 ≤ x ≤ 0.15) nanoparticles, which were synthesized using the proteic sol-gel process. The Rietveld refined XRD patterns confirmed the presence of M-type SrFe12O19, alongside a minor fraction of α-Fe2O3. As Sm³⁺ doping increased, the unit cell volume fluctuated, decreasing from 691.73 ų at x = 0 to 690.67 ų at x = 0.10 and slightly rising thereafter. The incorporation of Sm³⁺ induced a conversion of Fe3+ to Fe2+, affecting lattice parameters and crystallinity. At x = 0.10, maximum crystallite size (56.48 nm) and X-ray density (4.83 g/cm³) were attained, alongside decreased microstrain, indicating improved crystallinity and reduced defects. However, at x = 0.15, an increase in microstrain suggested lattice instability. FTIR confirmed that bands in the range 400–600 cm⁻1 might be due to the stretching vibration of oxygen and metal (Fe–O) ions, confirming the formation of hexaferrite. Temperature-dependent Raman spectroscopy studies confirmed the presence of spin-phonon coupling in all samples in the ferrimagnetic transition at ∼725-735 K. Mössbauer spectroscopy elucidated that the substitution of Sr2+ by Sm3+ induced the most pronounced effect on the 12k, 4f2, and 2a sites, corroborating the evolution of the lattice constants and the fact that these three sites have Sr sites in their close vicinity. The room-temperature hysteresis loops exhibited narrow features, indicative of soft magnetic behavior. Saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) varied with Sm3+ doping content (x). Ms initially decreased from 62.62 emu/g and 22.03 emu/g at x = 0.00 to 54.96 emu/g and 19.63 emu/g at x = 0.10, respectively, and then increase to 59.77 emu/g and 21.86 emu/g at x = 0.15. Conversely, Mr and Hc showed a non-monotonic trend with x, suggesting complex interactions between dopant concentration and magnetic properties.

Effect of Nb doping on the magnetic properties and its fluxgate behavior of CoFeNbSiB amorphous ribbons

Co-based amorphous alloys are often utilized as magnetic core for fluxgate sensor due to their excellent comprehensive performance with eminent permeability and insignificant coercivity. Herein, we investigated the effects of Nb doping on the phase composition, amorphous formation, magnetic domain structure and soft-magnetic characteristics of (Co0.7Fe0.5Si0.15B0.1)100-xNbx (x = 0, 1, 3, 5, 7) alloy ribbons and its fluxgate performance. Additionally, related magnetic parameters as magnetic permeability μi and coercivity Hc of the ribbon under zero magnetic-field annealing (ZFA) as well as longitudinal magnetic-field annealing (LFA) and fluxgate sensitivity and noise value were also tested. It is verified that the Nb doping is well able to optimize their amorphization, thermostability and soft magnetic properties. When x = 3, the ribbon presents the most well-distributed magnetic domain structure and the inferior soft magnetic properties, with an initial permeability μi of 8900 and a coercivity Hc of 1.51 A/m. Compared with ZFA, LFA is more effective on improving the soft magnetic and fluxgate behavior. The highest μi of 24,520 and the lowest Hc of 0.18 A/m are obtained at x = 3 for the LFA sample, where the fluxgate sensitivity is up to 44.15 mV/μT, accompanied by the peak-to-peak noise (denoted by Noisep-p) value is as low as 1.38 nT.

Electromagnetic absorption properties of FexCoNi magnetic nano particles

The microstructure morphology, static magnetic properties, and electromagnetic absorption characteristics of nano FexCoNi alloy particles prepared by chemical liquid deposition with five different Fe content levels are investigated in this paper. The results show that spherical FexCoNi alloy particles with an average particle size of about 100–200 nm and a face-centered cubic crystal structure were obtained. All five samples exhibited soft magnetic behavior, with the saturation magnetization intensity showing an increasing-then-decreasing trend with increasing Fe content, peaking at 141.8 emu/g for Fe content x = 1.0. The dielectric constants (real and imaginary parts) of the prepared alloy particles exhibit significant differences with respect to the variation of Fe content, while the changes in the real and imaginary parts of the magnetic permeability show less pronounced effects with increasing Fe content. As the electromagnetic wave frequency increases, the real parts of the dielectric constants for all composites show minimal fluctuations, and the real parts of the magnetic permeability exhibit a decreasing trend. Moreover, the imaginary parts of the dielectric constants and magnetic permeability show an increasing followed by a decreasing trend as the frequency rises. The material with Fe content x = 1 demonstrated optimal dielectric loss performance and relatively excellent magnetic loss performance, with a sample thickness of 1.9 mm exhibiting the highest reflection loss (RLmax) of −24.2 dB and an effective absorption bandwidth of 4.48 GHz.

Influence of growth temperature on the magnetization dynamics of sputtered CoFeB thin films on various substrates and their microwave device functionality

In the present investigation, sputtering growth of 100 nm thick Co40Fe40B20 (CoFeB) film has been investigated in a low temperature range from room temperature (RT) to 400 ℃ on silicon (Si), silicon dioxide (Si/SiO2), and sapphire (Al2O3) substrates. The film surface morphology, static and dynamic magnetization were measured as a function of growth temperature and substrate. The grown films were further tested as a potential material for microwave device functionality in terms of filter and phase shifter. Surface roughness was lowest for the film grown on Si/SiO2 substrate at 200 ℃ (0.39 nm) measured from atomic force microscopy. Static magnetic properties measured by tracing magnetic hysteresis loop suggest a soft magnetic behaviour with in-plane magnetic anisotropy. Film saturation magnetization increases with the increase in growth temperature up to 200 ℃ and then decreases from 200 ℃ to 400 ℃. This suggest that the sputtering growth from room temperature to 200 ℃ offer a moderate to low interfacial stress resulting in low defects density. Gilbert damping constant (αeff) of the thin film is obtained from the ferromagnetic resonance measurements in a broad band of microwave frequencies. Damping was lowest (5.4×10−3) in the film grown at 200 ℃ on the Si/SiO2 substrate which correlates with the roughness and magnetization data. A low value of αeff is desirable for a material to be used in energy efficient spintronics and magnonic applications. The CoFeB films were also utilized in prototype microwave band-stop filter and phase shifter device applications. The filter has been tested in the frequency range from 6GHz to 25GHz with an applied magnetic bias up to 4.0 kOe. The frequency tunability with respect to the applied magnetic bias measured to be around 3.64 GHz/kOe. The maximum attenuation of −4dB was observed for the film grown on Si/SiO2 substrate at 200 ℃. Whereas, phase shifter fabricated on Si/SiO2/CoFeB film grown at 200 ℃ shows a differential phase shift up to 75°/cm. These results indicates that the CoFeB film deposited at low growth temperature can be a potential material in spintronics and CMOS applications where low temperatures are required for device fabrications.

The Microstructure and Magnetic Properties of a Soft Magnetic Fe-12Al Alloy Additively Manufactured via Laser Powder Bed Fusion (L-PBF)

Soft magnetic Fe-Al alloys have been a subject of research in the past. However, they never saw the same reception in technical applications as the Fe-Si or Fe-Ni alloys, which is, to some extent, due to a low ductility level and difficulties in manufacturing. Additive manufacturing (AM) technology could be a way to avoid issues in conventional manufacturing and produce soft magnetic components from these alloys, as has already been shown with similarly brittle Fe-Si alloys. While AM has already been applied to certain Fe-Al alloys, no magnetic properties of AM Fe-Al alloys have been reported in the literature so far. Therefore, in this work, a Fe-12Al alloy was additively manufactured through laser powder bed fusion (L-PBF) and characterized regarding its microstructure and magnetic properties. A comparison was made with the materials produced by casting and rolling, prepared from melts with an identical chemical composition. In order to improve the magnetic properties, a heat treatment at a higher temperature (1300 °C) than typically applied for conventionally manufactured materials (850–1150 °C) is proposed for the AM material. The specially heat-treated AM material reached values (HC: 11.3 A/m; µmax: 13.1 × 103) that were close to the heat-treated cast material (HC: 12.4 A/m; µmax: 20.3 × 103). While the DC magnetic values of hot- and cold-rolled materials (HC: 3.2 to 4.1 A/m; µmax: 36.6 to 40.4 × 103) were not met, the AM material actually showed fewer losses than the rolled material under AC conditions. One explanation for this effect can be domain refinement effects. This study shows that it is possible to additively manufacture Fe-Al alloys with good soft magnetic behavior. With optimized manufacturing and post-processing, further improvements of the magnetic properties of AM L-PBF Fe-12Al may still be possible.

Composition dependent variation in structural, morphological, optical and magnetic properties of biogenic CuO/NiO mixed oxides nanoparticles

A series of CuO/NiO nanoparticles with different Cu and Ni precursor concentrations represented as N12 (1:2), N22 (1:1) and N21 (2:1) (Cu2+:Ni2+) were produced by modified green solution combustion route using Moringa oleifera leaves extract as an organic fuel. The prepared CuO/NiO nanoparticles were analytically characterized using UV-Vis diffuse reflectance spectroscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and vibrating sample magnetometry. Morphological studies showed uniform and nearly monodisperse nanoparticles having average grain size of 34 nm for N22 nanoparticles while the N12 and N21 compositions showed uniform nanoparticles with the grain size of 12 nm and 22 nm respectively. The existence of CuO and NiO phases in nanoparticles was verified by XPS analysis. N12, N22 and N21 had band gaps in the range of 2.19–2.49 eV and specific surface area in the range of 4.92–11.2 m2/g. The susceptibility vs. temperature plots for mixed oxides nanoparticles showed distinct magnetic behaviour for different ratio. The coercivity and saturation magnetization reached a maximum value for N22 (130 Oe and 0.133 emu/g). These biogenic nanoparticles could be a strong choice for biological applications due to their soft magnetic behaviour and biocompatibility.

Thermal stability and magnetic properties of the nanocrystalline (Fe64Co21B15)99Cu1 high-Bs alloy at elevated temperatures

In this study we present evolution of the soft magnetic behavior in nanocrystalline (Fe64Co21B15)99Cu1 high-Bs alloy after long-term exposure to elevated temperatures (200 and 250 °C). The investigated ribbons exhibit excellent stability of the soft magnetic properties after thermal aging for 100 h at 200 °C both under vacuum and ambient air conditions. Our results show that the rise of ageing temperature to 250 °C has led to a noticeable increase of coercivity for the air-annealed ribbon only, indicating an appreciable role of surface oxidation process.

Synthesis of large-sized spherical Co-C alloys with soft magnetic properties though a high-pressure solid-state metathesis reaction.

In this work, we report a novel high-pressure solid-state metathesis (HSM) reaction to produce spherical bulk (diameters 2-4 mm) Co-C alloys (Co3C and Co1-xCx). At 2-5 GPa and 1300 °C, C atoms preferentially occupy the interstitial sites of the face-centered cubic (fcc) Co lattice, leading to the formation of metastable Pnma Co3C. The Co3C decomposes above 1400 °C at 2-5 GPa, C atoms infiltrate the interstitial sites of the fcc Co lattice, saturating the C content in Co, forming an fcc Co1-xCx solid solution while the C atoms in excess are found to precipitate in the form of graphite. The Vickers hardness of the Co-C alloys is approximately 6.1 GPa, representing a 19.6% increase compared to hexagonal close-packed (hcp) Co. First-principles calculations indicate that the presence of C atoms in the Pnma Co3C structure leads to a relative decrease in the magnetic moments of the two distinct Co atom occupancies. The Co-C alloys exhibited a soft magnetic behavior with saturation magnetization up to 93.71 emu g-1 and coercivity of 74.8 Oe; coercivity increased as the synthesis pressure rises.

Zn-Co amorphous magnetic alloy from electrochemical deposition

Amorphous films of Zn-Co alloys presenting soft magnetic behavior were produced by electrodeposition on Cu substrates. Samples obtained potentiostatically at −1.4 V using solutions with 0.17 and 0.21 mol·L−1 of CoSO4, and 0.03 mol·L−1 of ZnCl2, resulted in films with 14 and 15 at.% of Co, respectively. These results contrast with polycrystalline samples with 5 at.% of Co obtained with 0.1 mol·L−1 of CoSO4 and 0.33 mol·L−1 of ZnCl2. The magnetic coercivities of the amorphous samples are smaller than 13 mT, while the polycrystalline sample does not present ordered magnetic behavior. The structure, morphology, composition, and magnetic behavior of the samples were analyzed.