Magnetocrystalline Anisotropy Field Research Articles

Effect of annealing temperature on crystallographic texture, magnetic and microwave properties of barium ferrite thin films

Due to it has large saturation magnetization (Ms), high magnetocrystalline anisotropy field and high ferromagnetic resonance (FMR) frequency, barium ferrite (BaM) has attracted more and more attentions in the fields of magnetic recording media, permanent magnets and microwave devices. Here, BaM thin films were deposited on Pt/TiO2/SiO2/Si substrates, and the effect of annealing temperature on the microstructure, magnetic and microwave properties of barium ferrite thin films was investigated in detail. It is found that when the BaM thin film was annealed at 1035 °C, it has good properties. The XRD data provide clear evidence that the BaM thin films have high c-axis orientation, and the Lotgering factor is as high as 0.96. The AFM morphology show that BaM grains are out of the film plane, and they are hexagonal. The magnetic hysteresis curves indicated that both saturated magnetization (4πMs), remanence ratio and coercive (Hc) for out of plane increase with increasing Ta first, then decreased, and get the maximum value at 1035 °C. The ferromagnetic resonance (FMR) measurement show that the FMR linewidth is 143 Oe@50 GHz, it means that this this sample has low microwave loss in millimeter wave loss, and the FMR absorption can be tuned by applied magnetic field. These results make sure that this BaM thin film is possible use in millimeter wave devices such as filers, circulators and isolators.

Modulation of magnetic properties in self-assembled one-dimensional CoxFe3-xO4 nano-chains with Co substitution

Modulation of magnetic properties on the low dimensional material under multiple fields is a captivating area of study in material science and nano-technology. In this paper, we focus on the self-assembly of chain-like nanostructures composed of CoxFe3−xO4 nanoparticles with an average size of 150 nm. These structures, consisting of more than 20 nanoparticles, are formed at 90 °C under a 0.25 T external magnetic field. The length of chains is surprising to decrease with increasing Co content due to an obvious additional cubic magneto-crystalline anisotropy superposed on the uniaxial induced anisotropy which is induced by the synthesized magnetic field with easy axis along the length of the chain. The additional magneto-crystalline anisotropy field of Co blocks the chain growing in length with Co doping. Additionally, our X-ray magnetic circular dichroism (XMCD) measurements confirm the doping of Co2+ ions in the CoxFe3−xO4 nano-chains, where they predominantly occupy the B sites and substitute the Fe2+ ions. This finding underlines the importance of spin-orbit coupling enhancement in the magnetic behavior resulting from the Fe2+ substitution with Co2+.

Towards the difference in coercivity enhancement of nanocrystalline Nd-Fe-B alloys with Pr and Ho substitution

Magnetocrystalline anisotropy field (HA) is an internal factor for determining the coercivity (Hc) of the magnetic materials. Despite a theoretical HA of 73 kOe, the melt-spun Nd-Fe-B alloy achieves only 20 % of this value for Hc. Comparing Ho2Fe14B and Pr2Fe14B compounds with an identical HA of 75 kOe, we reveal that Ho-substituted Nd-Fe-B alloys exhibit a more pronounced Hc enhancement than Pr-substituted alloys. The Hc value of (Nd1-xPrx)-Fe-B alloy increased from 16.9 kOe (x = 0) to 20.7 kOe of x = 1.0 alloy, achieving 28 % of its HA value. Notably, the Ho-substituted alloys exhibited a significantly higher coercivity, reaching 28.0 kOe at x = 1.0 and establishing an impressive 38 % ratio to its HA. The coercivity of Ho-substituted alloys is controlled by both nucleation and pinning, whereas the Pr-substituted alloys follow a nucleation-type mechanism. Microstructure characterization shows Ho substitution has a positive effect on grain refinement. Furthermore, Ho tends to concentrate in the RE2Fe14B grains, leading to an increased HA of the main phase and a substantial rise in Hc.

Influences of divalent ion substitution on the magnetic and dielectric properties of W-type barium ferrite

Abstract Saturation magnetization, magneto-crystalline anisotropy field and dielectric properties are closely related to microwave devices applied at different frequencies. For regulating the magnetic and dielectric properties of W-type barium ferrites, single-phase BaMe 2Fe16O27 (Me = Fe, Mn, Zn, Ni, Co) with different Me ions were synthesized by the high-temperature solid-state method. The saturation magnetization (M s) range from 47.77 emu/g to 95.34 emu/g and the magnetic anisotropy field (H a) range from 10700.60 Oe to 13739.57 Oe, depending on the type of cation substitution in the hexagonal lattice. The dielectric permittivity and dielectric loss decrease with increasing frequency of the AC electric field in the low-frequency region, while they almost remain constant in the high-frequency region. The characteristics of easy regulation and preparation make it a potential candidate for use in microwave device applications.

Cu2+/Dy3+ dual doped calcium based Ca1-xCuxFe12-xDyxO19 hexaferrites: Microstructural and magnetic properties for magnetic applications

The structural and magnetic behaviour of hexaferrite can be significantly altered by varying the sintering temperature and cationic subtitutions. Therefore, using the sol–gel route, we have synthesized M−type Ca1-xCuxFe12-xDyxO19 (x = 0.0, 0.05, 0.10, 0.15, 0.20) hexaferrite nanoparticles in the present research work. The samples' microstructure, phase, and magnetic characteristics are examined concerning different doping concentrations using SEM, XRD, and VSM. The analysis indicates a minor percentage of Fe2O3 phases in all samples. The refined lattice variables ‘a’ and ‘c’ are initially enhanced by increasing the level of doping upto x = 0.15 and then decreases. Similarly, the average crystallite size shows an increase continuously. The remanence and saturation magnetization rise first as the doping level increases, then show a minor change for the maximum doping level. Like this, as the doping content is raised, the coercivity and magneto-crystalline anisotropy field increased first and then showed a minor decrease. The sample with the best magnetic properties is Ca0.85Cu0.15Fe11.85Dy0.15O19 with Ms = 35.738 emu/g, mB(µB) = 6.732B, Mr = 20.430 emu/g, Hc = 3.15 kOe, and Mr/Ms = 0.572. All samples were excellent candidates for use in magnetic devices due to their high Mr/Ms values. The effect of doping on the magnetic features of M−type hexa-ferrites has made them useful in numerous applications, such as high-performance self-biased circulators, magnetic filters, and storage devices.

Ba2Co2-xZnxFe12O22 Hexaferrites produced by the method of self-propagating high-temperature synthesis: Structure, properties, application

In this study, Y-type hexaferrites Ba2Co2-xZnxFe12O22 (Co2-xZnx-Y, x = 0.0, 0.5, 1.0, 1.5) powders were synthesized by the method of self-propagating high-temperature synthesis. Hexaferrite powders were obtained both with and without preliminary mechanical activation before synthesis. A comprehensive analysis of the microstructure, morphology, phase composition and magnetic properties has been carried out. The synthesis conditions for obtaining hexaferrite powder with the highest content of the target phase are determined. An increase in the content of the target phase was revealed when using preliminary mechanical activation before synthesis. The magnetocrystalline anisotropy fields and magnetomechanical ratios for Ba2Co2-xZnxFe12O22 powder hexaferrites have been determined for the first time by ferromagnetic resonance method. The study of the spectra of reflection loss and permeability of composites made on the basis of Co2-xZnx-Y hexaferrites synthesized with preliminary mechanical activation showed that these composites can serve as an effective absorber to reduce side electromagnetic radiation in the frequency range of 6–18 GHz.

The effect of Nd content on the elemental interdiffusion mechanism of Nd–Dy–Fe–B magnets

In this work, the effect of Nd content on the interdiffusion mechanism of Nd/Dy elements in Nd-Dy-Fe-B magnets was elucidated by studying the differences in the magnetic properties, microstructure, and demagnetization process. As the Nd content increased, a uniform, continuous, and thicker layer of rare earth-rich (RE-rich) phase formed inside the magnets, which had a good magnetic isolation effect. During the demagnetization process, the strong ferromagnetic coupling effect between the main phase grains could be effectively weakened. At the same time, the thicker RE-rich phase layer could lead to a more obvious interdiffusion phenomenon of Nd/Dy elements, forming more (Nd, Dy)2Fe14B phases with high magnetocrystalline anisotropy fields, resulting in higher coercivity of the magnets. This paper elucidated the influence of Nd content on the interdiffusion mechanism of dual alloy Nd-Dy-Fe-B magnets, which had important significance for the preparation of high-performance Nd-Dy-Fe-B magnets.

A Novel Spinel Ferrite-Hexagonal Ferrite Composite for Enhanced Magneto-Electric Coupling in a Bilayer with PZT.

The magnetoelectric effect (ME) is an important strain mediated-phenomenon in a ferromagnetic-piezoelectric composite for a variety of sensors and signal processing devices. A bias magnetic field, in general, is essential to realize a strong ME coupling in most composites. Magnetic phases with (i) high magnetostriction for strong piezomagnetic coupling and (ii) large anisotropy field that acts as a built-in bias field are preferred so that miniature, ME composite-based devices can operate without the need for an external magnetic field. We are able to realize such a magnetic phase with a composite of (i) barium hexaferrite (BaM) with high magnetocrystalline anisotropy field and (ii) nickel ferrite (NFO) with high magnetostriction. The BNx composites, with (100 - x) wt.% of BaM and x wt.% NFO, for x = 0-100, were prepared. X-ray diffraction analysis shows that the composites did not contain any impurity phases. Scanning electron microscopy images revealed that, with an increase in NFO content, hexagonal BaM grains become prominent, leading to a large anisotropy field. The room temperature saturation magnetization showed a general increase with increasing BaM content in the composites. NFO rich composites with x ≥ 60 were found to have a large magnetostriction value of around -23 ppm, comparable to pure NFO. The anisotropy field HA of the composites, determined from magnetization and ferromagnetic resonance (FMR) measurements, increased with increasing NFO content and reached a maximum of 7.77 kOe for x = 75. The BNx composite was cut into rectangular platelets and bonded with PZT to form the bilayers. ME voltage coefficient (MEVC) measurements at low frequencies and at mechanical resonance showed strong coupling at zero bias for samples with x ≥ 33. This large in-plane HA acted as a built-in field for strong ME effects under zero external bias in the bilayers. The highest zero-bias MEVC of ~22 mV/cm Oe was obtained for BN75-PZT bilayers wherein BN75 also has the highest HA. The Bilayer of BN95-PZT showed a maximum MEVC ~992 mV/cm Oe at electromechanical resonance at 59 kHz. The use of hexaferrite-spinel ferrite composite to achieve strong zero-bias ME coupling in bilayers with PZT is significant for applications related to energy harvesting, sensors, and high frequency devices.

Synergetic effect of site-controlled two-step Ca doping on magnetic and electrical properties of M-type strontium hexaferrites

M-type strontium (SrM) hexaferrites exhibiting large magnetocrystalline anisotropy, high saturation magnetization and coercivity, and narrow ferrimagnetic resonance (FMR) linewidth have a great potential for applications in high-performance motors and self-biased circulators. Ca doping in SrM hexaferrites is an effective method for tailoring the intrinsic electromagnetic parameters and modifying polycrystalline microstructure to meet the application requirements. However, the regulation mechanism of Ca doping is still obscure, and its regulation effect is not optimized. Here, the magnetic and electrical properties of SrM hexaferrites with site-controlled two-step Ca doping are reported. The spatial concentration distribution and diffusion dynamics of Ca2+ ions are investigated when introduced by CaCO3 as the reactant and sintering additive, respectively. The existence of the Ca2+ ions in the crystallites added as the reactant reduces the diffusion of the Ca2+ ions in the grain boundaries added as the additive, which synergistically tailors the magnetocrystalline anisotropy field, crystallite orientation, and polycrystalline morphology, and further optimizes the coercivity, remanence, and maximum energy product. Moreover, the impact of the Ca2+ ions on the resistivities of the grain and grain boundary is also investigated, revealing the synergetic effect of Ca2+ ions at different sites on lowering the loss. These results prove the effectiveness of the site-controlled two-step Ca doping in synergistically enhancing the magnetic and electrical properties of SrM hexaferrites.

Coercivity mechanism of high-performance anisotropic heterostructure SmCo5 magnets

Due to its large magnetocrystalline anisotropy field and high Curie temperature, SmCo-based magnets are irreplaceable in high-temperature applications. The hot-deformed SmCo-based magnets are especially attractive for their excellent corrosion resistance, making them more suitable for harsh environments. However, it is still challenging for hot-deformed SmCo-based magnets to obtain high magnetization and high coercivity simultaneously. Therefore, it is necessary to analyze the relationship between its microstructure and magnetic properties and explore its magnetic hardening mechanism to guide the further improvement of magnetic properties. In this paper, the anisotropic heterostructure SmCo5 magnet was prepared by combining large height-reduction and introducing a nano-grained Sm-rich phase. Strong c-axis texture, (BH)m of 16.1 MGOe, and Hci of 9.6 kOe were obtained via the heterostructure with SmCo5 micron-grain and Sm-rich nano-scale precipitates. The magnetic domain observation and technical magnetization analysis demonstrate that the coercivity mechanism is dominated by nucleation. The results also show that the smooth and Sm-rich precipitated grain boundary provides weak pinning effects. It provides a reference for the development of high-performance nanocrystalline SmCo5 magnets.

Effect of ferromagnetic cobalt on characteristics of coercive Aluminium substituted BaFe11.5Al0.5O19 hexaferrites

Magnetic and structural characteristics of M-type barium hexaferrite nanoparticles can be tuned by doping different di or trivalent metal ions. Here BaFe11.5−xAl0.5CoxO19 hexaferrite nanoparticles were synthesized using a sol-gel process, and the influence of doping concentrations on M-type BaFe11.5−xAl0.5CoxO19 hexaferrite nanoparticles was deliberated. The XRD analysis confirms the formation of ferrites successfully. When the doping level increased, the grain dimension (D) initially reduced and then increased. Similarly, the lattice constants ‘a’ and ‘c’ decreased initially and then increased. The findings indicated that the (Mr/Ms) ratio decreased initially as the doping content increased, but at higher doping ranges, it started to rise. At the same time, coercivity (Hc) and magneto-crystalline an-isotropy field (Ha) increased as the doping level increased. Excellent magnetic characteristics were obtained for BaFe11.5−xAl0.5CoxO19 hexaferrites at doping content of (x = 1.5), with magnetic moment 10.80 μ B, saturation magnetization 57.35 emu g−1, and coercivity 5.21 kOe along anisotropic applied field of 1.62 kOe. The findings mentioned above imply that magnetic characteristics of M-type Barium hexaferrites can be significantly improved upon doping of Cobalt against Aluminium substituted hexaferrites, which will make such types of Ba-hexaferrites very useful in various magnetic applications.

Pr–Tb synergistic strengthening on coercivity of Nd-Ce-Fe-B magnets grain boundary diffused with Pr-Tb-Al-Ga alloys

Sintered Nd-Ce-Fe-B magnets were grain boundary diffused (GBDed) with PrxTb80–xAl10Ga10 (at%) (x = 0, 20, 40, 60, 80) alloys. The effect of Pr/Tb content in diffusion source on magnetic properties, microstructure and elements distribution of GBDed magnets was investigated. When Pr is used to substitute for 75% Tb in diffusion source, Tb consumption per unit coercivity improvement of GBDed magnet reduces by 77%, compared with the Tb80Al10Ga10 diffused magnet. Tb element diffuses into magnets and then forms Tb-rich shell with high magneto-crystalline anisotropy field surrounding main phase grains, resulting in substantial coercivity improvement. Pr with low melting point diffuses deeply along liquid grain boundary phase during GBD process. It can eliminate some sharp defects of main phase grains and make grain boundaries smooth, which provides diffusion channels for further diffusion of Tb element. Therefore, there are more diffusion channels for Tb and less Tb enriched at surface region, making Tb diffuse more deeply and improving Tb utilization efficiency. This method significantly improves the coercivity, and realizes the green, efficient and high-quality utilization of heavy rare earth (HRE) elements.

Structural and magnetic properties of BaFe9.95Al2Mg0.05O19 tuned through sintering temperature

The sintering temperature is a key way to tune the structural and magnetic properties of M-type hexaferrites. Here the effect of BaFe9.95Al2Mg0.05O19 M-type hexagonal Ba-hexaferrites, was studied. X-ray diffraction analysis revealed the presence of Fe2O3 impurity phases in all samples. The results showed that as the sintering temperature increased, the saturation magnetization (Ms) and remanence ratio (Mr/Ms) initially increased, then decreased at higher temperatures. On the other hand, the coercivity (Hc) and magnetocrystalline anisotropy field (Ha) decreased first, then increased. The average grain size (D) consistently grew between 800–2800 nm with increase in pre-sintering temperature. The optimal magnetic properties of BaFe9.95Al2Mg0.05O19 were achieved at a pre-sintering temperature of 1280 °C, with Ms = 49.94 emu g−1, Hc = 4.99 kOe, Ha = 1.5 kOe, and mB = 9.4097 μB. The findings suggest that magnetic properties of M-type hexagonal strontium ferrite can be significantly enhanced by optimizing the pre-sintering temperature, which has implications for the development of high-performance self-biased circulators, Magnetic filters and other magnetic applications.

Rusticle magnetotaxis elucidating Rustflower formations in RMS Titanic's Turkish Baths

During his bio-archaeological Last Mysteries of the Titanic expedition in 2005, explorer James Cameron observed the RMS Titanic's Turkish Baths, an anoxic chamber secluded from currents deep within the wreck's remote interior, utilizing the ROV Skipper. There, Cameron discovered anomalously thin, vertical, and bifurcating rusticle formations he termed “Rustflowers.” Proposing magnetotaxis as the involved mechanism, this study analyzed rusticles salvaged from Titanic's #8 davit bitt utilizing ferromagnetic resonance, which demonstrated an asymmetric spectrum featuring prominent uniaxial over magnetocrystalline anisotropy fields of Buni = 110 mT and Bcub = −23 mT, linewidth parameters of ΔB = 200 mT, ΔBFWHM = 144 mT, ΔBhigh = 37 mT, ΔBlow = 107 mT, and asymmetry ratio of A = 0.35, and α = 0.20. These represent the established signature of biogenic magnetofossil chains synthesized by former magnetotactic bacteria, enduring within the rusticle cortex. Electron microscopy and chemical analysis identified single-domain range magnetite nanocrystals, and crystalline elemental sulfur inclusions, respectively. Chemosynthetic microbial iron oxy-hydroxide accretions guided upward along geomagnetic field lines by north-seeking magnetotaxis, under reducing conditions exhibited in Titanic's Turkish Baths, may account for the distinctive morphology of its Rustflowers; adding dimension to the bacterial application of iron assimilated from deep-sea sources, including shipwrecks.

Microstructure and magnetic properties of grain boundary diffused Nd-Fe-B magnets with Tb-Al-Ga alloy

The coercivity of Nd-Fe-B magnets can be effectively improved by grain boundary diffusion using low melting point alloy as diffusion source. In this work, Tb-Al-Ga alloy was used as diffusion source for grain boundary diffused Nd-Fe-B magnets. Tb-rich shell structure, potential synergistic effect of Al-Ga, interface between diffusion source and the magnets were analyzed. When the magnets were processed at 875 °C for 10 h, the coercivity increased by 123 % from 10.38 kOe to 23.15 kOe and the remanence and the maximum magnetic energy product only decreased by 3 %. Tb element mainly formed shell structure with high magneto-crystalline anisotropy field surround the main phase grains. Non-magnetic Al element was distributing around the main phase grains as network structure, which could well isolate the main phase grains. The Tb-rich shell with high magneto-crystalline anisotropy field and the non-magnetic phase with magnetic exchange decoupling between the adjacent grains contributed to substantial increase in the coercivity of the grain boundary diffused magnets. The grain boundary phase was wetted by Al element, which promoted Tb element diffused into the magnets more deeply.

Microstructure regulation and optimizing magnetic properties of (La, Ce, Pr)17Fe78B6 alloy via short-range grain boundary diffusion

Increasing the utilization ratio of La and Ce in rare earth permanent magnets is an effective measure to solve the balance utilization of rare earth resources. In this work, nanocrystalline melt spun [(Ce0.7La0.3)0.3Pr0.7]17Fe78B6 powder and low melting point PrTbCu alloy were used as the initial material and the diffusion source for short-range grain boundary diffusion (SRGBD) to improve the coercivity. High coercivity of up to 18.21 kOe can be achieved, enhancing by 108.82% compared with the initial powder, and meanwhile, the remanence was only slightly reduced by 2.13%. After that, nanocrystalline bulk magnets with excellent magnetic performance were produced through spark plasma sintering (SPS). TEM observation reveals that the bcc-RE2O3 intergranular phase that induced by short-range grain boundary diffusion is distributed between adjacent matrix phase grains, which is conductive to the improvement of magnetic isolation effect. EDS results show that the Tb-rich shell with high magnetocrystalline anisotropy field has formed. Moreover, it is found that Tb diffuses into the 2:14:1 phase more easily than Pr element during the initial stage of diffusion. Enhanced magnetic isolation effect and the formed Tb-rich shell in grain surface contributed to high coercivity.

Fe and Cr co-intercalation in 2H-NbS2 single crystals for realization of perpendicular magnetic anisotropy and large anomalous Hall effect

Recently, many interesting magnetic and electrical properties have been demonstrated in transition-metal intercalated $2\text{H-Nb}{\mathrm{S}}_{2}/\mathrm{Ta}{\mathrm{S}}_{2}$ layered single crystals. In this work, single crystals of Cr and Fe co-intercalated $2\text{H-Nb}{\mathrm{S}}_{2}$, with the compositions of ${({\mathrm{Cr}}_{1--x}{\mathrm{Fe}}_{x})}_{1/3}\mathrm{Nb}{\mathrm{S}}_{2} (x=0.0--1.0)$, are successfully grown and their magnetic and transport properties are systematically studied. With increasing Fe content, the magnetic transition temperature continually decreases from 117 to 37 K, and the magnetic coupling transforms from ferromagnetic to antiferromagnetic. Importantly, a rotation of the magnetic easy axis occurs in this process, with perpendicular magnetocrystalline anisotropy and considerable coercive field achieved in the $x=0.13--0.66$ compounds. Both $x=0.33$ and $x=0.50$ exhibit relatively low carrier concentration, stable anomalous Hall effect, and butterfly-shape magnetoresistance. Notably, large anomalous Hall conductivity is identified in $x=0.50$, whose origin is discussed from the calculated electronic structures. The realization of perpendicular anisotropy and large anomalous Hall conductivity in this two-dimensional ferromagnetic system can facilitate their future application in spintronic devices.

Enhancement of coercivity and thermal stability of Pr85Al15 doped NdFeB sintered magnets followed with grain boundary diffusion

Magnetic-property modification and thermal stability improvement for high-performance NdFeB magnets by dual-alloy (DA) sintering with Pr85Al15 (PrAl) together with grain boundary diffusion (GBD) with Tb55Pr20Cu25 (TbPrCu) is demonstrated. The coercivity is increased from 14.9 to 16.4–18.0 kOe for the magnet DA sintering with 2–4 % PrAl. Pr and Al at grain boundary strengthens magnetic decoupling effect. In addition, a thin layer of (Nd, Pr)2Fe14B with higher magnetocrystalline anisotropy field (HA) is formed at grain surface. Both effects contribute to the coercivity enhancement for the magnets prepared by DA sintering with PrAl. Furthermore, remarkable coercivity enhancement, from 14.9 to 18.0 kOe to 22.7–27.1 kOe, with improved thermal stability is attained for the above magnets after GBD with Tb55Pr20Cu25 alloy. Besides, the increased Curie temperature of 2:14:1 phase indicates the entrance of Tb into 2:14:1 phase and helps to improve thermal stability. Most importantly, various magnetic levels of high-performance NdFeB magnets, including 48–52 M, 45H, 50SH and 40-45UH, can be easily attained by modifying the amount of PrAl for DA sintered magnets and/or GBD with TbPrCu alloys.

Phase stability and coercivity in La2Fe14B magnet

Critical rare-earth free La2Fe14B (2:14:1) has the potential to be a gap permanent magnet. However, La2Fe14B decomposes into La, α-Fe, and LaFe4B4 phases below 1067 K. The phase stability and coercivity have been studied in La2Fe14B magnet using first principles DFT (density functional theory) calculation and micromagnetic simulation. For a perfect La2Fe14 B cube (edge length of 256 nm) without any structural defects and soft magnetic secondary phases, the coercivity (8.5 kOe) is reduced to ∼40% of its magnetocrystalline anisotropy field (HA = 20 kOe). Further, the coercivity sharply reduces to 3.2 kOe upon forming a thin layer (2 nm) of α-Fe on the surface of the La2Fe14B cube particle. The DFT calculations indicate that a partial replacement of La by other rare-earth (RE) elements can enhance the structural stability of 2:14:1. The gains in cohesive energy are 0.75, 0.10, and 0.33 eV per formula unit in (La0.5RE0.5)2Fe14B with RE = Ce, Pr, and Nd, respectively. Stabilizing the 2:14:1 structure and mitigating the formation of soft magnetic structural defects or impurity phases such as α-Fe is necessary to develop La2Fe14B based magnet, which can be moderately achieved via partial substitution of La by other rare earth elements such as Ce, Pr, and Nd.

Tunable magnetocrystalline anisotropy and high-frequency magnetic properties of Y2(Co1−xFex)17 and their composites

Rare-earth transition-metal (R-T) intermetallic compounds are emerging as competitive candidates for novel microwave absorption materials (MAMs) since they show high magnetization and tunable easy magnetization directions (EMDs). In this work, Y2(Co1−xFex)17 (0 ≤ x ≤ 0.3) compounds with the Th2Ni17 hexagonal structure were prepared with the purpose of tuning the EMDs. As x increases, the EMDs of the Y2(Co1−xFex)17 compounds change from the ab-plane (0 ≤ x < 0.0329) to the cone (0.0329 ≤ x ≤ 0.038) and then to the c-axis direction (0.038 < x ≤ 0.3). Furthermore, it was found that the extremely high cutoff frequencies of the uniaxial anisotropy materials give them considerably potential for microwave absorption applications above 10 GHz, despite their relatively low initial permeability compared to the planar anisotropic materials. By studying the high-frequency properties of Y2(Co1−xFex)17/paraffin composites, it is noted that uniaxial anisotropy compounds with x = 0.1 and x = 0.3 can possess higher permeability above 10 GHz as compared to both planar anisotropy and conical anisotropy compounds (x < 0.1) due to their high cutoff frequencies arising from large magnetocrystalline anisotropy fields. This can improve the impedance matching and thus lead to a better microwave absorption performance in the range of 10 to 40 GHz for materials with uniaxial anisotropy. Among all the compositions, the Y2(Co0.9Fe0.1)17/paraffin composite exhibits a minimum reflection loss (RL) of −50 dB at 6 GHz with a thickness of 2.5 mm and a wide qualified bandwidth (QB, RL < −10 dB) of 9.6 GHz at a center frequency of 30.3 GHz with a thickness of 0.6 mm, thus making it a promising candidate for MAMs above 10 GHz.