Ce2Fe14B Phase Research Articles

A novel grain refinement of Ce-Fe-B magnets induced by magnetic field annealing

Magnetic field annealing-induced grain refinement usually occurs during the crystallization process of amorphous alloys. This work investigates the effects of magnetic field annealing on the microstructure and magnetic properties of crystalline Ce17Fe76Co1Zr0.5B6Mo0.5 alloys. The results indicate that magnetic field annealing below the Curie temperature (TC) of the Ce2Fe14B phase in the alloys reduces the alloy’s grain size. At an annealing temperature of 433 K, the average grain size of alloys decreased from 48.0 nm in the as-spun sample to 27.2 nm in the magnetic field annealing sample. Moreover, magnetic field annealing can effectively reduce the volume fraction of the CeFe2 phase in the alloy. After magnetic field annealing at 433 K, the alloy obtained the optimal comprehensive magnetic properties: the intrinsic coercivity (Hci = 441.1 kA/m), remanence (Br = 0.49 T), squareness (Hk/Hci = 0.53), and maximum energy product ((BH)max) = 35.5 kJ/m3), which were 0.2 %, 16.7 %, 6 %, and 29.1 % higher than the values of the as-spun sample, respectively. Precession electron diffraction (PED) analysis revealed that magnetic field annealing increased strain at grain and phase boundaries and a more uniform grain orientation spread (GOS), promoting recrystallization and grain refinement. This study provides new insights into the grain refinement mechanism of crystalline alloys under magnetic field annealing, contributing to further improving the magnetic properties of Ce-Fe-B magnets.

Dependences of Magnetic Properties on the Grain Size and Hard/Soft Magnetic Phase Volume Ratio for Ce2Fe14B/α-Fe and Nd2Fe14B/α-Fe Nanocomposites.

The magnetic properties of magnetic nanocomposites consisting of hard and soft magnetic phases are dependent not only on the intrinsic properties but also on the grain structure and volume ratio of the two phases. In this study, we performed a systematic micromagnetic simulation on the magnetic properties of Ce2Fe14B/α-Fe and Nd2Fe14B/α-Fe nanocomposites. The volume fractions of the hard magnetic Nd2Fe14B or Ce2Fe14B phase were varied from 80% to 40%, and the grain sizes of the hard magnetic phase and the soft magnetic α-Fe phase were changed independently from 10 nm to 40 nm. The results show that when the grain size of both hard and soft phases is 10 nm and the volume fraction of the hard phase is 70%, the highest maximum magnetic energy product can be obtained in both Ce2Fe14B/α-Fe and Nd2Fe14B/α-Fe nanocomposites. The hard magnetic properties of Ce2Fe14B/α-Fe nanocomposite decrease significantly when the volume fraction of the α-Fe phase exceeds 30%. However, for the Nd2Fe14B/α-Fe system, this situation only occurs when the α-Fe volume fraction exceeds 40%. The reason for this is not only because of the low anisotropic field and the smaller exchange coupling length between the soft and hard magnetic phases, but also because of the lower saturation magnetization of the hard phase. The grain size has greater effects on the magnetic properties compared to the volume fraction of the hard magnetic phase. The main reason is that as the grain size increases, the remanence of the nanocomposite decreases sharply, which also leads to a rapid decrease in the maximum magnetic energy product. The simulation results on the effects of phase ratio and grain size have been verified by experiments on melt-spun Ce2Fe14B/α-Fe alloys with various compositions prepared by melt-spinning followed by annealing for various lengths of time. Due to the influence of demagnetization energy, the hard magnetic phase with high saturation magnetization is preferred for the preparation of high-performance nanocomposite magnets.

Enhanced magnetic properties of Ce17Fe76.5Co1Zr0.5B6 alloys by magnetic field heat treatment

In the present work, Ce17Fe76.5Co1Zr0.5B6 ribbons were prepared by a direct melt spinning method. The effects of chamber pressure and magnetic field annealing temperature on the magnetic properties and microstructures of the alloys were investigated. The grain size and content of Ce2Fe14B phase can be changed by adjusting the chamber pressure, and the optimal magnetic performance is obtained at 0.04 MPa. The magnetic properties can be influenced under magnetic field heat treatment. When the annealing temperature is lower than the Curie temperature, the refinement and a uniform distribution of the grains is obtained. The irreversible magnetic susceptibility curve reveals that magnetic field heat treatment enhances the exchange coupling interaction between grains of the Ce2Fe14B phase. When the magnetic field annealing temperature is 438 K, the alloy displays the optimal magnetic properties. Compared with the as-spun sample, the values of intrinsic coercivity (Hci), remanence (Br) and maximum energy product ((BH)max) increase by 3.4%, 9.8% and 18.7%, respectively. This work provides an effective approach by which to enhance the magnetic properties of Ce–Fe–B alloys.

Effect of the Ga Content on the Magnetic Properties and Microstructure of the Nanocrystalline Ce-Fe-B Alloys

In this work, the Ce17Fe78-xB6Gax (x = 0~3) nanocrystalline alloys are prepared by the direct melt spinning method with the wheel speed of 18 m/s. The effect of Ga content on the hard magnetic properties and the crystal structure of Ce17Fe78-xB6Gax (x = 0~3) nanocrystalline alloys has been investigated. The results show that the Curie temperature (Tc) and the phase content hard magnetic Ce2Fe14B phase can be increased by adding appropriate amount of low melting point Ga element. The results of magnetic properties show that the enhanced magnetic properties are obtained for the alloy with x = 1: Hcj = 5.61 kOe, Br = 5.4 kG, Hk/Hcj = 0.49, and (BH)max = 5.1 MGOe. The magnetization reversal characteristics of the alloys are analyzed by the recoil loops and the δM-H curves; the sample with the Ga-doped shows a single hard magnetic behavior. The positive peak of δM-H curve of the sample (x = 1) is obviously sharper and the peak value is higher, indicating the strongest magnetic interaction between grains. The reasons of the enhanced magnetic properties for the Ce-Fe-B alloy by the Ga addition are analyzed depending on the microstructure.

Phase Structure, Microstructure, and Magnetic Properties of (Nd-Ce)13.4Fe79.9B6.7 Alloys

Phase structure and microstructure of (Nd1-xCex)13.4Fe79.9B6.7 (x = 0.0–1.0) alloys that were prepared via the arc-melting method were studied experimentally in this work. The results reveal that (Nd1-xCex)13.4Fe79.9B6.7 alloys annealed at 1173 K for 360 h are a single (NdCe)2Fe14B phase with the tetragonal Nd2Fe14B-typed structure (space group P42/mnm). The formation of continuous (NdCe)2Fe14B solid solution phase in annealed (Nd1-xCex)13.4Fe79.9B6.7 alloys was confirmed. On the other hand, magnetic measurements exhibit that the coercivity, remanence, maximum magnetic energy product, and Curie temperature of (Nd1-xCex)13.4Fe79.9B6.7 ribbons that were fabricated by melt spinning technology decrease gradually with increasing Ce content, which results from the substitution of Nd by Ce in Nd2Fe14B phase due to inferior intrinsic magnetic properties of Ce2Fe14B phase.

Improvement of magnetic properties for Ti doped Ce-Fe-B alloys: Effectively inhibiting CeFe2 phase formation

In the present work, the effect of the partial substitution of Fe by Ti on the magnetic properties, Curie temperature and microstructure of Ce17Fe78-xTixB6 (x = 0–5 at.%) alloys are thoroughly investigated. The results reveal that the optimal magnetic properties of Br = 4.8 kG, Hcj = 5.45 kOe, Hk/Hcj = 0.47, Br/Bs = 0.64, (BH)max = 5.4 MGOe have been obtained for the x = 1 alloy heat treated at Ta. Meanwhile, it is shown that the addition of a small amount of Ti can decline the volume fraction of the paramagnetic CeFe2 phase and contribute to form more magnetic Ce2Fe14B phase, while the grain size of the Ce2Fe14B phase could not be effectively optimized due to the higher optimum treatment temperature Ta. The results of Henkel plot show that the Ti-doped alloy with a higher positive δM value and narrower peak is in charge of the enhanced magnetic properties.

Magnetic properties, thermal stability, and microstructure of spark plasma sintered multi-main-phase Nd-Ce-Fe-B magnet with PrCu addition

Nanostructured multi-main-phase (MMP) Nd-Ce-Fe-B magnet produced by melt-spinning powders has great potential for achieving high performance. However, the inferior intrinsic properties of the Ce2Fe14B phase lead to the low coercivity and thermal stability of this magnet. In this study, low-melting-point Pr68Cu32 powders were introduced into nanostructured MMP magnet through intergranular addition to further improve its coercivity and thermal stability. When only 2 wt% Pr68Cu32 was added, the intrinsic coercivity Hcj and thermal stability were significantly improved with a slight reduction in the remanence Br and the maximum energy product (BH)max. The microstructure evolution of MMP magnet with adding Pr68Cu32 was revealed by microstructural and compositional characterization and thermodynamic calculation, and a schematic model was proposed. Furthermore, mechanisms underlying changes in magnetic properties were systematically analyzed by combining micromagnetic simulation.

Phase and microstructure formation of strip-cast Ce–Fe–B alloys for multi-phases RE-Fe-B magnets

The starting alloy has a strong influence on the processing and the magnetic properties of the sintered magnets. Aiming at the preparation of the high-performance low-cost (Nd, Ce)–Fe–B magnets, the phase constitution and microstructure of Ce–Fe–B alloy are systematically investigated in this work. The results showed that Ce2Fe14B phase coexists with CeFe2 phase in the Ce–Fe–B alloy. A fairly high proportion of 2:14:1 phase (～93.1%) and column crystals structure which is similar to that of Nd-Fe-B alloy could be obtained by regulating the composition of Ce–Fe–B alloy. Owing to the structure optimization of Ce–Fe–B alloy, the sintered magnet which possessed a microstructure of fine grains together with smooth and continuous grain boundaries could maintain the superior magnetic properties of Br = 13.1 kGs, Hcj = 7.79 kOe and (BH)max = 40.49 MGOe by the mixture of (Pr, Nd)12.75Fe80.25M1.0B6.0 and Ce17FebalM2.0B6.0 (M = Al, Cu, Ga, Nb in at.%). This work thus provides useful guideline for the preparation of Ce-doped hard magnets.

Microstructure, magnetic anisotropy, plastic deformation, and magnetic properties: The role of PrCu in hot deformed CeFeB magnets

The usages of high-abundance rare-earth element Ce in the permanent magnet have drawn considerable interest from industrial and scientific societies. In this work, through PrCu addition combined with grain boundary diffusion process (GBDP), anisotropic hot deformed (HD) CeFeB magnets with Jr = 0.66 T, Hci = 514 kA/m, and (BH)max = 55 kJ/m3 can be acquired. The addition of intergranular phase PrCu in spark plasma sintering (SPS) is favorable to the improvement of the plastic deformation ability and the increase of the c-axis crystallographic texture of HDed magnet. Meanwhile, it can also act as a diffusion channel to increase the diffused efficiency during the subsequent GBDP. The observed three Curie temperatures on M-T curves, should be attributed to three various types of 2:14:1 phase, that is initial Ce2Fe14B phase and different (Pr, Ce)2Fe14B phases formed in the process of spark plasma sintering (SPS) and GBDP, respectively. Elemental metallurgical behavior revealed that, the intergranular phases are rich in Pr, Ce, and Cu but depleted in Fe. Intergranular phases analysis demonstrated that, Pr and Ce oxides including (Pr, Ce)O2, Pr12O22, and (Pr, Ce)2O3 can be identified, and amorphous phase is also observed. Through GBDP, magnetic properties, including the coercivity, remanence, and maximum energy product are all improved greatly, which is ascribed to the joint effects from the formation of (Pr, Ce)2Fe14B phase and intergranular phase.

Suppressing the CeFe2 phase formation and improving the coercivity and thermal stability of Ce-Fe-B alloys by Si substitution

Low anisotropy field and low Curie temperature of Ce2Fe14B phase seriously restrict the application of Ce-Fe-B alloys. Most of the previous work suggest that REFe2 phase inevitably forms in the compositions with high Ce content. In this work, Si substitution for Fe is found to not only suppress the formation of CeFe2 phase, but also significantly improve the coercivity Hc and thermal stability of Ce17Fe78-xSixB6 (x = 0–3.0) alloys. All Si-doped alloys exhibit higher Hc and better thermal stability than Ce17Fe78B6 alloy. With increasing Si doping, a relatively high Hc = 525 kA/m is obtained in the Ce17Fe77.75Si0.25B6 alloy. An abnormal increase of Hc as well as almost unchanged Jr and (BH)max is observed in Ce17Fe78-xSixB6 (x > 1.5) alloys. The refined XRD results indicate that the volume fraction of CeFe2 phase can be dramatically reduced via a moderate content of Si doping. Hard magnetic grains are isolated by forming a structure with thin and continuous intermediate layer, consequently preventing the domain wall propagation. The Curie temperature of the main phase monotonically increases from 424 K for x = 0–445 K for x = 3.0, resulting in improved thermal stability. The highest Hc of 530 kA/m, the lowest temperature coefficients (|β| = 0.551%/°C and |α| = 0.368%/°C), and an acceptable Jr = 0.44 T are obtained in Ce17Fe78-xSixB6 (x = 3.0) alloy. The nucleation and pinning are both responsible for the coercivity mechanism of Ce17Fe75Si3B6 alloy, which should be the reason for its high coercivity.

Synthesis of nanocrystalline Ce13Fe81B6 alloy through mechanically driven disproportionation-recombination process

Nanocrystalline Ce13Fe81B6 alloy powder was synthesized by mechanically driven disproportionation-recombination processing. The microstructure transformation of the alloy during different processing stages was characterized by XRD and TEM. The magnetic properties of the nanocrystalline powder were measured by VSM. The results showed that the Ce2Fe14B matrix phase of the Ce13Fe81B6 alloy was disproportionated into the nanostructured CeH2.51, α-Fe, and Fe2B phases by ball milling in hydrogen for 20 h, and that these nanostructured phases could be desorbed and recombined to nanocrystalline Ce2Fe14B phase again by subsequent vacuum annealing, with the remanence, coercivity, and maximum energy product of the as-synthesized alloy powders achieving 8.1 kGs, 6.02 kOe, and 8.51 MGOe, respectively.

Effect of magnetic layer thickness on magnetic properties of Ce-Fe-B thin films

The Ce2Fe14B thin films with a notable out-of-plane c-axis texture were prepared by DC magnetron sputtering on a Ta buffer layer. The morphological and magnetic properties were investigated. The thickness of the magnetic layer had a dramatic effect on the formation of Ce2Fe14B phase, and excellent magnetic properties (Hci ≈ 4.25 kOe, Mr/Ms ≈ 0.81) were observed for the Ce-Fe-B film with the thickness dm = 200 nm. The results of the hysteresis loops for Ce-Fe-B film (dm = 200 nm) at various measured temperatures show that a decoupling between the hard and the soft phases is observed at low temperatures, which is due to the regions with quite low anisotropy provided by the α-Fe. Moreover, it is clear that significantly various magnetization behaviors between the films with dm = 200 and 300 nm were observed with a similar trend due to the existence of the α-Fe soft phase.

Study on Magnetic and Corrosion Properties of Ce<sub>16</sub>Fe<sub>95-x</sub>Co<sub>x</sub>B<sub>8</sub> (x=0-4) Alloys

To understand the phase composition and improve the magnetic performances of Ce2Fe14B-type alloys, the ribbons of Ce16Fe95-xCoxB8(x=0-4.0) were prepared by melt-spinning at a quench wheel velocity of 40 m/s. The phase composition and magnetic properties of Ce16Fe95-xCoxB8(x=0-4.0) alloys were investigated. XRD results indicated that the main phase existed in the as-spun ribbons is Ce2Fe14B. The amorphous formation ability and thermal stability of as-spun ribbons were enhanced by trace cobalt addition. Co-doped samples had higher Curie temperature compared with bare Ce2Fe14B, which signified that Co atoms could substitute for Fe directly into Ce2Fe14B phase. The corrosion potential of alloys from-1089mV (vs. SCE) to-1077mV (vs. SCE) which indicated that the Co-doped provided better corrosion protection properties for the Ce-Fe-B magnet compared with bare substrate.

Effect of Heat Treatment on Microstructure and Magnetic Properties of Ce-Doped NdFeB Ribbons

The substitution for Nd by abundant element cerium (Ce) is a practical way for the comprehensive utilization of rare earth resources in NdFeB permanent magnets. In this letter, we have prepared the Ce-doped NdFeB ribbons and conventional NdFeB ribbons by melt quenching method and investigated the effects of heat treatment on the crystallization behavior, microstructure, and magnetic properties of the alloy. The results show that: (1) The crystallization behavior and the microstructural changes of the (Nd,Ce)FeB magnets are similar to the conventional NdFeB magnet when heat treatment. In addition, the Ce2Fe14B phase has a significant effect on the properties of the whole magnets. (2)The NdFeB phase and CeFeB phase are relatively close to each other after being precipitated from the amorphous phase. The coupling effect between the two phases is strong enough to weaken the effect of the addition of Ce and making the properties of the NdFeB magnets to not reduce too much after adding Ce.

Gd substitution for Ce in preparing (Ce,Gd)-Fe-B magnets

Ce-Fe-B rare-earth alloys are alternative to substitute partially for Nd-Fe-B permanent magnets for reducing the cost and the balance use of rare-earth elements. However, coercivity is rather low in Ce-Fe-B magnets, which partially ascribes to the instability of Ce2Fe14B phase and the low magnetocrystalline anisotropy. In this paper, magnetic properties are investigated in Ce13-xGdxFe81B6 ribbons via substituting of Gd for Ce. X-ray diffraction shows that a little amount of Gd substitution for Ce leads to an increase in the intensity of diffraction peak for main phase, which should be attributed to the improvement of the stability of R2Fe14B phase and the reduction in the amount of amorphous phase. Even though the magnetocrystalline anisotropy is lower in Gd2Fe14B than that in Ce2Fe14B, the coercivity increases to 5.88 kOe for a little amount of Gd substitution in Ce12Gd1Fe81B6 ribbons. For Gd atomic percent more than 3% the coercivity decreases, and the remanence drops significantly. With the increase of Gd atomic percent, Curie temperature increases monotonically. Henkel plots indicate that Gd substitution for Ce could enhance the effect of exchange coupling, which owes to the increase of exchange coefficient in main phase as well as to the reduction in the amount of amorphous phase. These investigations show that a little amount substitution of Gd is beneficial to improve the magnetic properties without a significant drop of the remanence.

A Cost-Effective Approach to Optimizing Microstructure and Magnetic Properties in Ce17Fe78B₆ Alloys.

Optimizing fabrication parameters for rapid solidification of Re-Fe-B (Re = Rare earth) alloys can lead to nanocrystalline products with hard magnetic properties without any heat-treatment. In this work, we enhanced the magnetic properties of Ce17Fe78B6 ribbons by engineering both the microstructure and volume fraction of the Ce2Fe14B phase through optimization of the chamber pressure and the wheel speed necessary for quenching the liquid. We explored the relationship between these two parameters (chamber pressure and wheel speed), and proposed an approach to identifying the experimental conditions most likely to yield homogenous microstructure and reproducible magnetic properties. Optimized experimental conditions resulted in a microstructure with homogeneously dispersed Ce2Fe14B and CeFe2 nanocrystals. The best magnetic properties were obtained at a chamber pressure of 0.05 MPa and a wheel speed of 15 m·s−1. Without the conventional heat-treatment that is usually required, key magnetic properties were maximized by optimization processing parameters in rapid solidification of magnetic materials in a cost-effective manner.

Phase precipitation behavior of melt-spun ternary Ce2Fe14B alloy during rapid quenching and heat treatment

To understand the structure, phase precipitation and magnetic properties of the ternary Ce-Fe-B alloy, the effects of wheel speed and heat treatment on the melt-spun Ce2Fe14B alloy have been investigated. For the wheel speeds varied from 10 to 50m/s, hard magnetic Ce2Fe14B phase precipitates in as-spun ribbons prepared at 10 and 20m/s. Increasing wheel speed leads to the appearance and increase of amorphous phase and reduced saturation magnetization. For the amorphous ribbons prepared at 50m/s, when the annealing temperature increased from 500°C to 600°C and 700°C, α-Fe phase precipitates first followed by the appearance of Ce2Fe14B phase and grain growth. Transmission electron microscope analysis revealed that large Ce2Fe14B grains and the uniformly distributed small α-Fe grains precipitates from amorphous matrix after heat treatment. The good magnetic properties with saturation magnetization of 11.7kG, remanence of 5.7kG, coercivity of Hc=2.8kOe, and maximum energy product of 2.9MGOe have been obtained in the optimized sample.

Structure, magnetic properties and Mössbauer study of melt-spun nanocrystalline Ce-rich ternary Ce-Fe-B alloy

Nanocrystalline ternary Ce-Fe-B alloys with a composition close to a Ce16Fe78B6 were prepared by melt spinning. The phase constitution and microstructure of the alloys were investigated by X-ray diffraction and Transmission Electron Microscopy. 57Fe Mössbauer spectrometry was employed, allowing first to quantify the different phases, i.e. Ce2Fe14B and CeFe2, and then to estimate the values of their respective hyperfine characteristics. By combining with the magnetic measurements, the magnetic moments of both Fe and Ce atoms in Ce2Fe14B phase were estimated based upon the Wigner-Seitz analysis of the RE2Fel4B structure. This work thus provides useful and relevant information for the investigation and applications of Ce-based hard magnets.

Variations of phase constitution and magnetic properties with Ce content in Ce-Fe-B permanent magnets

Magnetic materials of Ce12+xFe82−xB6 (x=0, 0.5, 1, 1.5, 2, and 3) containing mainly Ce2Fe14B phase were prepared by melt spinning method. The coercivity is the lowest in Ce12Fe81B6 ribbons. With the increase of Ce content, the coercivity increases monotonically, and X-ray techniques show that the amount of minor phase Fe3B decreases but the amount of CeFe2 increases. Magnetization reversal and magnetic properties are dependent on the amount of minor phases. The squareness of hysteresis loop is the best in Ce13.5Fe80.5B6 ribbons with energy product of 6.80MGOe. Optimizing the phase constitution is necessary to improve magnetic properties in Ce-based alloys for utilizing the rare earth resource in a balanced manner.

Study on magnetic properties of Ce17Fe78−xZrxB6 (x=0–2.0) alloys

In order to improve the magnetic performances of Ce2Fe14B-type alloys, Ce17Fe78−xZrxB6 (x=0–2.0) were synthesized by a melt spinning method at a quench wheel velocity of 35m/s. The crystal structure and hard magnetic properties of Ce17Fe78−xZrxB6 (x=0–2.0) alloys were investigated. The glass forming ability and thermal stability of as-spun ribbons were improved by Zr addition. Zr-doped samples had lower Curie temperature for Ce2Fe14B, implying that Zr atoms could substitute directly into Ce2Fe14B phase. Refinement of X-ray diffraction data showed that the lattice constants and volume fraction of Ce2Fe14B phase for Ce17Fe78−xZrxB6 (x=0–2.0) alloys annealed at optimum temperatures decreased gradually with increasing Zr content. Moreover, the mean grain size of the Ce2Fe14B phase decreased gradually with Zr at% increasing from 0 to 2.0. The analysis of Henkel plots verified that proper Zr content improved the microstructure and enhanced the exchange coupling interaction. When x=0.5, the optimum magnetic properties were obtained: iHc=429.9kA/m, Br=0.48T and (BH)max=4.5MGOe.