Optimum Magnetic Properties Research Articles

Novel Fabrication Method for a High-Performance Soft-Magnetic Composite Composed of Alumina-Coated Fe-Based Metal Powder

A high-performance soft-magnetic composite (SMC) has been successfully fabricated in a toroidal mold without the application of compaction pressure by mixing three different alumina-coated Fe-based metal powders, namely carbonyl iron (FM), Fe-Si-Cr alloy (FSC), and Fe-Si-Al alloy (sendust), with epoxy resin in a centrifugal paste mixer. Surface coating with an alumina layer was performed via a sol–gel process, and its thickness was controlled by varying the coating time. Without the alumina coating, the SMC toroidal core with a FM:FSC:sendust mixing ratio of 8:22:70 by mass exhibited optimal magnetic properties including an effective permeability (μeff) of 33.9 and total core loss (Pt) of 252 mW/cm3 at 100 kHz with an amplitude (B) of 50 mT. With the alumina coating, however, the SMC toroidal core with the same mixing ratio exhibited a significantly reduced Pt value of 213 mW/cm3 while its μeff value was slightly decreased to 32.4, primarily due to the suppression of the macroscopic eddy-current loss from 115 mW/cm3 to 85 mW/cm3. These results indicate that an optimal mixture of the three different alumina-coated Fe-based metal powders is very effective for fabricating high-performance SMC cores without external pressure for molding, being applicable for miniature electronic components.

Effect of Cu addition on microstructure, texture and magnetic properties of 6.5 wt% Si electrical steel

The effect of Cu addition in the range of 0 – 1.0 wt% on the magnetic induction and iron loss of 6.5 wt% Si electrical steel is investigated. The microstructure and texture of the steels are also analysed to reveal the mechanisms by which their magnetic properties after annealing are affected by Cu addition. Cu addition up to 0.7 wt% is found to increase magnetic induction B50 although the increase is very small due to the formation of η-fiber texture. The iron loss of 6.5 wt% Si electrical steel decreases with increasing Cu addition to up to 0.5 wt%, but increases with further Cu addition. When Cu addition is increased to 0.7 wt%, the iron loss for this steel becomes higher than for that without Cu addition. Microstructural analysis suggests that Cu addition of up to 0.5 wt% can promote the recrystallization during annealing and increase the recrystallized grain size, leading to a decrease in iron loss. With further increase in Cu addition, especially beyond 0.7 wt%, large numbers of fine ε-Cu precipitates form in the microstructure during warm-rolling, which inhibit grain growth during annealing. This is the main reason for the observed increase in iron loss when Cu addition is over 0.5 wt% Cu. The Cu addition range for achieving the optimum magnetic properties for 6.5 wt% Si electrical steel is 0.3 – 0.5 wt%.

The effect of processing parameters on magnetic properties of an epoxy resin-bonded isotropic Nd–Fe–B magnet

Ring-shaped epoxy resin-bonded magnets were fabricated using an isotropic nano-crystalline melt spun Nd–Fe–B powder. The magnets were produced from a mixture of the isotropic powder and some epoxy resins as binders, using a compression-molding technique. The morphology and average particle size of the powders were examined using an SEM. The magnetic properties of the magnets were evaluated using a hysteresis loop tracer. The effects of milling time, binder type and content, hardener amount, lubricant percentage, pressing pressure, and curing temperature and time on magnetic properties of magnets were studied. It was found that the magnetic properties of the bonded magnets were the best in an as-received condition of ribbons, and any particle size reduction by milling results in reduction in permanent magnetic properties. The best magnetic properties were attained for the bonded magnets produced using a two-component air-dried liquid epoxy resin. The optimized binder content, lubricant percentage, pressing pressure, curing temperature and time in these magnets were as: 3 wt%, 0.4 wt%, 900 MPa, room temperature and 24 h, respectively. The optimal magnetic properties were as follows: Br = 7 kG, HcJ = 9.10 kOe and (BH)max = 11.5 MGOe. However, the best thermal stability was obtained when the bonded magnets were produced using a solid powder epoxy resin with a special aromatic hardener.

Investigation on the grain boundary diffusion of Dy2O3 film prepared by electrophoretic deposition for sintered Nd-Fe-B magnets

Based on the diffusion source of Dy2O3 film prepared by electrophoretic deposition (EPD), grain boundary diffusion (GBD) is performed to improve properties of sintered Nd-Fe-B magnets. Effects of EPD and GBD processes on microstructure and magnetic properties are investigated in details. The studied results show that 30 s of EPD time is the most suitable for the preparation of diffusion source, and the optimal magnetic properties with Hci of 934 kA/m, Br of 1.41 T and (BH)max of 349 kJ/m3 can be achieved under GBD condition of 800 °C/6 h followed by 500 °C/1 h, enhancing by 27.6%, 0.7% and 13.7%, respectively, comparing to those of as-prepared magnet. The formation of (Nd, Dy)2Fe14B shell surrounding Nd2Fe14B core and improved distribution and structure of rare earth-rich (RE-rich) phase jointly contribute to the improvement of coercivity. Moreover, Thermal stability (temperature coefficient of remanence and coercivity) is improved considerably. Dense Dy2O3 film and formed filamentous substance covering the surface together promote the improvement of corrosion resistance.

Optimum Soft Magnetic Properties of the FeSiBNbCu Alloy Achieved by Heat Treatment and Tailoring B/Si Ratio

To increase the saturation magnetization (Ms) of commercially available soft magnetic Finemet alloys to the level comparable to that of Si-steel and Fe-based nanocrystalline alloys such as Nanoperm, Nanomet, the B or Si content in combination with annealing heat treatment was tailored. The ribbons of Fe95−xSi1BxNb3Cu1 (x = 11, 12, 13) and Fe87−xSixB9Nb3Cu1 (x = 6, 8, 10) were prepared by melt-spinning and annealed at different temperatures to develop nanocrystalline microstructure optimizing the soft magnetic properties. The magnetic properties of the as-spun and annealed ribbons were measured using a vibrating sample magnetometer and AC B-H loop tracer to acquire Ms of above 1.4 T in all as-spun ribbons. Among the alloys, Fe84Si1B11Nb3Cu1 annealed at 545 °C showed the highest Ms of 2 T, which exceeds that of the conventional Finemet and other Fe-based nanocrystalline alloys.

Investigation on structure, dielectric and magnetic properties of the four-layer Aurivillius phase Pb1-xBi3.5+xNd0.5Ti4-xMnxO15 prepared via molten salt method

In this study, the four-layer Aurivillius phases, Pb1-xBi3.5+xNd0.5Ti4-xMnxO15 (x ​= ​0, 0.1, 0.3, and 0.5), were prepared by the molten salt method, in order to investigate the effects on crystal structure, morphology, dielectric and magnetic properties of varying x composition. XRD patterns revealed that of the all samples were single-phase products with an orthorhombic structure. The refinement result demonstrates a compressive unit cell volume with increasing x composition. Moreover, FTIR spectroscopy showed a single mode of BO6 octahedra, and the shifting of this mode indicates that the Mn3+ ions occupy the perovskite B-site. The anisotropic plate-like grain was probed by SEM, the size of which showed an increase with a higher x composition, as the proportion of Bi3+ increases. The dielectric properties also increase with an increasing x composition, which results from the increasing structural distortion and grain size. The investigation of the magnetic properties indicates that the ferromagnetic behavior for the x ​= ​0.5 sample, presumably originated from the double-exchange interactions between Mn3+ and Mn4+ and the spin canting of distorted Mn(1)O6 octahedra via the Dzyaloshinskii–Moriya interaction. The formation of the mixed-valent Mn3+/Mn4+ could likely be caused by the oxidizing environment, produced by the oxobasicity properties of the sulfate salt in this molten-salt method. Therefore, the multiferroic properties exhibited at room temperature were due to the optimum dielectric and magnetic properties that were obtained at x ​= ​0.5.

Influence of microstructure and texture evolution on magnetic properties attained by annealing of a cold-rolled Fe-Co-10V semi-hard magnetic alloy

Typically, in processing of Fe-Co-V type magnetic alloys, hot rolled sheets are being severely cold rolled and then annealed at a specific temperature for an appropriate soaking time. In this work, in order to achieve the optimal magnetic properties, effect of various annealing cycles after 86% cold rolling on a 40Fe-50Co-10V (wt%) alloy were examined and the correlation between magnetic properties and microstructure and texture evolution was investigated. In order to supplement extensive microstructure evolution data available from previous publications, texture analysis was carried out using X-ray and electron backscatter diffraction methods and magnetic properties were determined via a vibrating sample magnetometer. It was observed that by increasing the annealing temperature the saturation magnetization decreased due to the formation of paramagnetic (Co,Fe)3V precipitates and austenite, while the coercivity increased in a reverse manner. The impact of austenite on decreasing the saturation magnetization was more pronounced than that of precipitates. Phase boundaries were more effective than grain boundaries in promoting the coercivity. However, nano-size (Co,Fe)3V precipitates inside the ferromagnetic matrix were also important in enhancing the coercivity. Besides formation of the precipitates, variations of the intensity of 〈111〉 direction as hard magnetic direction and intensity of {111}〈112〉 texture component, led to the alteration of magnetic remanence attained at 500–750 °C. Based on application of these alloys as semi hard and hard magnets, the optimal magnetic properties are achieved at a temperature range of 550–650 °C.

Bio-synthesised black α-Cr2O3 nanoparticles; experimental analysis and density function theory calculations

A selective single phase black α-Cr2O3 nanoparticles was bio-synthesised via simple straight-forward green synthesis approach. The process involves extraction of phytochemicals contained in peels of sweet potatoes. Extraction was done in distilled water under constant magnetic stirring at a temperature of 70–80 °C resulting in a dusty yellow colour aqueous extracts. Afterwards, chromic nitrate salt was added to extracts resulting in reduction of metal salt to metal nanoparticles. Obtained precipitates were dried and annealed in the air for 2 h ready to be applied without further post synthesis modifications. SEM and EDS analysis of annealed precipitates reveal distinct shapes and high purity of nanoparticles. The effects of the annealing temperature are evident in the nanoparticle sizes. SAED and XRD patterns expose bright diffraction peaks which are harmonized to the rhombohedral structure of pure Eskolaiteα-Cr2O3. By quantitative analysis of XRD data, it was noted that lattice parameters and crystal sizes slightly decrease w.r.t increase annealing temperature. Raman spectra recorded peaks ascribe to vibrations in A1g and Eg mode whereas FTIR analysis show absorption bands at 641 and 632 cm−1 which evidence the presence of α-Cr2O3 nanoparticles. UV–Vis absorbance peak generated Cr2O3 nanoparticles are observed at 402 nm yielding a band gap of 3.08eV. Magnetism results of α-Cr2O3 nanoparticles shows linear increase upon field increasing, which can be elucidated by the existing of uncompensated spins at the surface of the nanoparticles that may lead to nonmagnetic or antiferromagnetic state. Zero field cooling (ZFC) results of α-Cr2O3 nanoparticles were analysed based on Curie-Wien relation which yield values of magnetic moment (μeff) of the synthesised Cr2O3 nanoparticles close to the value that was assigned for Cr2+.The density functional theory (DFT) with the PW91, PBE, PBESOL and a Hubbard U Coulomb interactionwas utilized to study the optimum structure, electronic and magnetic properties of antiferromagnetically ordered Cr2O3. The computed results are consistent with the experimental measurements.

The Effect of Doping Cu Powders on Mechanical Properties and Magnetic Properties of Sm(CoFeCuZr)z Sintered Magnets

The effect of doping Cu on the mechanical properties and magnetic properties of Sm(Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.71</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.07</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.03</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7.6</sub> magnets was studied systematically. The results show that the Cu-lean grain boundaries and bending strength of the magnet can be improved by increasing of doping Cu content. The optimal magnetic properties of magnet with 1.0 wt% Cu doping are B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 9.9 kG, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> = 23.0 kOe, and (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 22.2 MGOe. With the doping content of Cu powders, the bending strength first reaches a peak value of 143.0 MPa at 1.0 wt% and then drops. The bending strength of the magnet with 1.0 wt% Cu doping is about 51.8% higher than that of the magnet with 0 wt% Cu doping. The coercivity and bending strength of the magnet are improved.

Electrochemical synthesis and magnetic properties of Nd-Fe-B-Tb nanowires

Nd-Fe-B-Tb nanowires were synthesized in AAO templates by electrodepositon through doping Tb3+ into Nd-Fe-B solution. The as-deposited nanowires are composed of Fe and amorphous phases, showing soft magnetic properties. Annealing makes Nd-Fe-B nanowires consist of Nd2Fe14B, Fe3B and NdB4 phases and exhibits hard magnetic characteristic due to the formation of hard Nd2Fe14B, Fe3B phases. After adding Tb3+, some new (Nd,Tb)2Fe14B, Tb2Fe14B, Fe3Tb and TbB50 phases, form in annealed nanowires. The existence of (Nd,Tb)2Fe14B and Tb2Fe14B phases with high anisotropy fields, the interface elastic coupling effect between different phases and the coherent phase interface increases the coercivity and remanence. Nd-Fe-B-Tb nanowires exhibit the optimal comprehensive magnetic properties at 0.05 mol/L Tb3+ concentration due to the highest content of Tb2Fe14B phase.

Structure and magnetic properties of alnico 8 ribbons

Alnico 8 ribbons were prepared by melt-spinning and annealing, and the effects of melt-spinning speeds on the structure and magnetic properties were investigated. The results show that all the as-spun ribbons are composed of the α-Fe(Co)-type α1 and the AlNi-type α2. With speed reducing from 40 m/s to 15 m/s, the <100> preferred orientation enhanced, the grain size and the α2 content increased. The as-spun ribbons show the weak hard magnetic properties. Annealing improves the spinodal structure consisting of the strip-like α1 and α2. The annealed ribbons melt-spun at 15 m/s achieve the optimal magnetic properties with the coercivity of 1558.3 Oe and the maximum magnetic polarisation density of 11.3 kGs, which are codetermined by the shape anisotropy of the strip-like α1 phase and the pinning mechanism of the α2 phase to the α1 domains.

Normal Electrochemical Deposition NiFe

Due to heating of the electrolyte is an excluded abnormal codeposition alloy components and reduced variation of process parameters to achieve optimal magnetic properties Ni81Fe19 films of magnetic field concentrators. Proposed chloride electrolyte pH adjusted with hydrochloric acid, which provides congruent electrochemical deposition of permalloy at heating and stirring. Magnetic properties of permalloy films are very sensitive to the variation of component relationships of 4.26. Control of accuracy of preparation of chloride electrolyte for electrochemical deposition of NiFe conducted using spectrophotometry. It is shown that the selection process of cooking the electrolyte for electrodeposition of Ni81Fe19 alloy and temperature allow to get normal, congruent electrochemical deposition of permalloy films. It has been established that the anomalous character of permalloy deposition associated with the main feature of iron ions-the existence of variable Valence iron with two or three values in the charge of ions during the hydrolysis of iron salts.

Normal Electrochemical Deposition NiFe

Due to heating of the electrolyte is an excluded abnormal codeposition alloy components and reduced variation of process parameters to achieve optimal magnetic properties Ni81Fe19 films of magnetic field concentrators. Proposed chloride electrolyte pH adjusted with hydrochloric acid, which provides congruent electrochemical deposition of permalloy at heating and stirring. Magnetic properties of permalloy films are very sensitive to the variation of component relationships of 4.26. Control of accuracy of preparation of chloride electrolyte for electrochemical deposition of NiFe conducted using spectrophotometry. It is shown that the selection process of cooking the electrolyte for electrodeposition of Ni81Fe19 alloy and temperature allow to get normal, congruent electrochemical deposition of permalloy films. It has been established that the anomalous character of permalloy deposition associated with the main feature of iron ions-the existence of variable Valence iron with two or three values in the charge of ions during the hydrolysis of iron salts.

Microstructure characteristics and optimization of 2:17-type Sm-Co sintered magnets with different iron content

In this work, the dependence of microstructure and magnetic properties on the iron content for Sm(CobalFexCu0.073Zr0.024)7.6 (x = 0.226, 0.233 and 0.24) magnets has been systematically studied. The magnet with x of 0.226 (relatively low Fe content) shows a homogeneous microstructure and optimal magnetic properties after it has undergone a solid solution treatment for only 2 h at 1443 K. However, under the same solid solution treatment, a largely uneven composition distribution is observed in magnets with an increased Fe content (x = 0.24). As a result, the peak and gradient of Cu concentration in the cellular boundaries are lower, giving rise to poor magnetic properties. It is impressive that there Cu precipitates are found in the as-solutionized magnet though the cellular structure has not yet occurred. Our results show that a prolonged solid solution treatment (ts) is necessary to improve the microstructure and magnetic properties of the magnets with higher Fe content. Moreover, the optimal ts can be shortened by increasing the solid solution temperature (Ts). However, when the Ts is too high, the composition is not uniform but segregated, and the magnet shows poor magnetic properties as well. Furthermore, it is also found that the homogeneous microstructure and optimal magnetic properties are deteriorated when the magnets undergo a solution treatment at much higher Ts. However, it can be recovered if the magnet is further solution treated at the proper conditions. Our results suggest that the transformation of microstructure and magnetic properties can be controlled reversibly by adjusting the solution treated conditions.

Preparation and properties of hot-deformed magnets processed from nanocrystalline/amorphous Nd–Fe–B powders

The hot-deformed magnets processed from nanocrystalline/amorphous Nd–Fe–B powders were prepared under different hot-pressing temperatures (600–750 °C, at intervals of 25 °C) by the self-made hot-pressing equipment. The microstructure and magnetic properties of hot-deformed magnets prepared at different temperatures were also investigated. When the temperature is above 650 °C, the density of magnet reaches 7.5 g·cm−3. The optimum magnetic properties of magnetic induction intensity of Br = 1.3 T, optimum energy product of (BH)max = 282.5 kJ·m−3, intrinsic coercivity of Hcj = 1130.0 kA·m−1 of hot-deformed magnets are obtained at hot-pressing temperature of 650 °C. X-ray diffractometer pattern shows that the (00L) texture has been obtained. For the microstructural characteristic, on the one hand, the good magnetic performance is attributed to the fine platelet-like grains with an average length of 410–440 nm at the hot-pressing temperature range from 625 to 675 °C. On the other hand, the unaligned coarse grains are observed in all the samples. And the areal fraction of those is gradually increasing with the rise of the hot-pressing temperature, which tends to deteriorate the magnetic properties. The composition map shows the accumulation of Nd/Pr-rich phase in the coarse grains’ region.

Elevated temperature behavior of rapidly quenched La/Ce substituted nanocrystalline NdFeB alloys with various compositions

Here we report the elevated temperature behaviors of rapidly quenched La/Ce substituted nanocrystalline NdFeB alloys with a wide range of compositions, including nano-composites of (Nd0.8Ce0.2)10Fe84B6, (Nd0.9La0.1)10Fe84B6, [Nd0.7(La0.5Ce0.5)0.3]10Fe84B6 and [Dy0.7(La0.5Ce0.5)0.3]10Fe84B6, single phase alloys of (Nd0.95La0.05)12Fe82B6 and (Nd0.8Ce0.2)12Fe82B6, as well as Co substituted single phase [Nd0.7(La0.5Ce0.5)0.3]12Fe72Co10B6 and RE-rich phase [Nd0.7(La0.5Ce0.5)0.3]14Fe70Co10B6 alloys. All compositions were fabricated by melt spinning technique. For nanocomposite alloys, the optimum high temperature magnetic properties at 400 K including remanent magnetization (Mr), maximum energy product (BH)max and coercivity (Hc) up to 89 emu/g, 65 kJ/m3, 226 kA/m, respectively, for Ce-substituted alloy and 70 emu/g, 46 kJ/m3 and 246 kA/m, respectively, for La-substituted alloys have been obtained. The decrease of Hc is ascribed to the microstructure sensitivity of La/Ce substituted NdFeB nanocomposite alloys at higher temperature. For single phase alloys, the optimum magnetic properties such as Mr, (BH)max and Hc up to 81 emu/g, 67 kJ/m3, 412 kA/m and 77 emu/g, 53 kJ/m3 and 349 kA/m have been obtained for La-substituted and Ce-substituted alloys at 400 K, respectively. The Ce-substituted alloys are relatively more sensitive to the elevated temperature compared to La-substituted alloys for both composites and single phase alloys. Substitution of 10% Co for Fe in both single phase and RE-rich phase alloys leads to the excellent elevated temperature magnetic properties at 400 K. The existing results state that La, Ce or LaCe substitutions for Nd and partial substitution of Co for Fe maintain a rather good combination of improved Curie temperature and elevated temperature magnetic properties at or above 400 K in all alloys with various phase constitutions.

Structural Change and Magnetic Properties of Mechanically Alloyed Spinel Ferrite CoFe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;

Magnetic property studies and the crystallite structures evolution of spinel ferrite CoFe2O4 particles are reported in this paper. The ferrite was prepared through mechanical milling of all alloy precursors and sintered at various temperatures of 800, 900, 1000, and 1100 °C to promote the crystalline structure. X-ray diffraction (XRD) and Williamson-Hall plot were used to calculate the mean crystallite size and microstrain. Changes in the microstructure and crystallite sizes were occurring due to sintering treatments. It is found that the remanence (Mr) and saturation magnetization (Ms) increase with increasing sintering temperature, but a decrease occurred only at the temperature of 1100 °C. The optimum magnetic properties were obtained in a sample sintered at 1000 °C with a value of Mr = 36.00 emu/g and Ms= 74.05 emu/g.

Assessment of the Textured State of the Nonoriented Electrical Steel for Electromobiles and the Effect of the Texture on the Basic Magnetic Characteristics

The structure and texture in recrystallized sheets of nonoriented electrical steel rolled according to different modes have been studied in this work. It has been shown that a decrease in the degree of deformation upon the final rolling leads to an increase in the ratio of the volume fractions of orientations that are favorable and unfavorable for the formation of optimal magnetic properties.

Effect of Ce on phase formation and magnetic properties of (Nd–Pr)2.28Fe13.58B1.14 melt-spun ribbons

The phase formation of the (Nd0.70Pr0.30−xCex)2.28Fe13.58B1.14 (x = 0.10, 0.15, and 0.20; hereafter defined as Pr20Ce10, Pr15Ce15 and Pr10Ce20, respectively) and (Nd0.60Pr0.40−yCey)2.28Fe13.58B1.14 (y = 0.10, 0.20, and 0.30; hereafter defined as Pr30Ce10, Pr20Ce20 and Pr10Ce30, respectively) alloys that were prepared via the arc-melting method was investigated experimentally. The x-ray diffraction results revealed that all alloys annealed at 1173 K for 360 h consisted of a (NdPrCe)2Fe14B main phase with a tetragonal Nd2Fe14B-typed structure (space group P42/mnm) and an α-Fe minor phase, except for the Pr10Ce30 alloy, which contained an additional CeFe2 phase. The magnetic properties of the (Nd0.70Pr0.30−xCex)2.28Fe13.58B1.14 and (Nd0.60Pr0.40−yCey)2.28Fe13.58B1.14 ribbons that were prepared by melt spinning were examined. The remanence (Br) and maximum magnetic energy product ((BH)max) of the (Nd0.70Pr0.30−xCex)2.28Fe13.58B1.14 ribbons increased first and then decreased, whereas the coercivity (Hcj) of the ribbons increased with an increase in Ce content. The Br and (BH)max of the (Nd0.60Pr0.60−yCey)2.28Fe13.58B1.14 ribbons increased, whereas the Hcj of the ribbons decreased gradually with an increase in Ce content. This changed behavior of magnetic properties is attributed to the variation of volume fraction of the α-Fe phase and different phase formations in the melt-spun ribbons. The Curie temperatures (Tc) of all ribbons decreased slightly with Ce substitution, which results from the lower Curie temperatures of Pr2Fe14B and Ce2Fe14B. The Pr10Ce30 ribbon with a higher Ce content exhibited optimal magnetic properties (Br = 9.71 kGs, Hcj = 13.09 kOe, (BH)max = 18.78 MGOe), which indicates that suitable magnetic properties of the Nd–Pr–Ce–Fe–B melt-spun ribbons can be achieved by alloy-composition and phase-formation design.

Broadband free space impedance in Co2Z hexaferrites by substitution of high valency heavy transition metal ions for miniaturized RF devices

Polycrystalline samples of Z-type hexaferrites, having nominal compositions Ba3Co2+xFe24−2xMxO41, where M = Ir, Hf, or Mo and x = 0 and 0.05, were processed via ceramic protocols in pursuit of low magnetic and dielectric losses, as well as equivalent permittivity and permeability over the VHF–UHF band. Fine process control was conducted to ensure optimal magnetic properties. Organic dispersants, i.e., isobutylene and maleic anhydride, were employed to achieve maximum densities. Crystallographic structure, characterized by x-ray diffraction, revealed that the dopants did not adversely affect the crystal structure and phase purity of the Z-type hexaferrite. An increase in permeability and size reduction factor is shown to be linearly proportional to the ionic radii of the dopants. This trend is consistent with local bonding distortions giving rise to increased exchange energy (J) as predicted by the Goodenough–Kanamori–Anderson rules and superexchange theory. We posit that these distortions increase the magnetocrystalline anisotropy energy affecting the frequency dependent complex permeability. For Mo doping of x = 0.05, a bandwidth of 400 MHz exists at a center frequency of 650 MHz where the permittivity and permeability are very nearly equal, i.e., Z = 377 ± 5 Ω. These results give rise to low loss, i.e., tan δε/ε′ = 0.0006 and tan δμ/μ′ = 0.038 at 650 MHz, with considerable size reduction (×9). The miniaturization and optimized performance of magnetodielectric materials for antenna at VHF–UHF frequencies using cost-effective and volumetric processing methodologies are demonstrated.