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We report a magnetically-anisotropic PrCo5 permanent bulk magnet, prepared by a hot deformation method, with crystallographic orientation-dependent magnetic properties. Although the PrCo5 crystals strongly favor the {0001} orientation texture, the crystallographic orientation textures of PrCo5 crystallites differ at various radial locations. From the bulk center to the edge, the c-axis orientation texture decreases from 5.4 MRD to 4.1 MRD, whereas the remanence decreases from 8.93 kGs to 7.58 kGs and the coercivity increases from 4.34 kOe to 6.56 kOe. This paper also reports the alteration of boundary plane orientation textures, resulting from the corresponding energy anisotropy at different locations, and suggests that the development of grain boundaries with lower boundary energies has a significant impact on the magnetic properties with regard to remanence and energy density. The current work therefore proposes an elegant approach to attain desired magnetic properties in PrCo5 magnets by fine-tuning the crystallographic orientation. [ABSTRACT FROM AUTHOR]

Effects of Zr addition and annealing treatment on the formation, microstructure and magnetic properties of Nd12.3Fe81.7− x Zr x B6.0 ( x=0−3.0) ribbons melt-spun and annealed have been systematically investigated by means of vibrating sample magnetometer (VSM), differential scanning calorimeter (DSC), X-ray diffraction (XRD), and high resolution scanning electron microscopy (HRSEM). Phase analysis reveals that Nd2Fe14B is single-phase material. It has been found that the intrinsic coercivity H ci of the optimally processed Nd12.3Fe81.7− x Zr x B6.0 ribbons increases monotonically from 751.7 kA/m for x=0 to 1005.3 kA/m for x=3.0. The remanence polarization J r and maximum energy product ( BH)max increase first with Zr addition, then slightly decrease with further increasing Zr content. Optimum magnetic properties with J r=1.041 T, H ci=887.5 kA/m and ( BH)max=175.2 kJ/m3 have been achieved for the ribbons with x=1.5. The significant improvement of magnetic properties originates from the finer grains of the ribbons by introducing Zr. [ABSTRACT FROM AUTHOR]

As a kind of magnetostrictive ceramics, cobalt ferrites are widely concerned because of its large magnetostriction and high resistivity, which are ideal for high-frequency applications. But, the high driving magnetic field due to the high magnetocrystalline anisotropy limits the practical applications of cobalt ferrites, thus, it is a still a challenge to find a balance between high magnetostriction properties and low driving magnetic fields. In this work, we investigated the effects of partially substitution of Ga3+ for Fe3+ on grain orientation and magnetic properties, attempting to maintain high magnetostriction while reducing the driving magnetic field. The CoFe 2-x Ga x O 4 (x=0, 0.05, 0.1, 0.15) with single-phase spinel structure were prepared by the conventional solid-state method. The saturation magnetization M S increased with the increase of Ga concentration, meanwhile the coercivity H c and magnetocrystalline anisotropy constant K 1 significantly decreased, which indicates the better soft magnetic characteristics of the Ga-doped cobalt ferrites. The oriented CoFe 2-x Ga x O 4 samples were obtained using magnetic field orientation technique during the powder forming process. The <001> preferred orientation was achieved in CoFe 2 O 4 samples. However, the <001> orientation degree decreased with the substitution of Ga, and the preferred orientation has changed into <111> at x=0.15. The Ga substitution affected the magnetocrystalline anisotropy and grain orientation, thereby affecting the magnetostrictive properties. As for the non-oriented samples, although the maximum magnetostrictive strain slightly decreased with Ga substitution, while there was a significant drop in the magnetostrictive saturation field. However, the magnetostriction of the oriented samples decreased significantly with the substitution of Ga due to the change of grain orientation from <001> to <111>. [ABSTRACT FROM AUTHOR]

The effects of composition on magnetic properties of sintered NdFeB are generally revealed by trial-and-error method, which is actually time-consuming and resource-intensive. It has been demonstrated that data-driven machine learning (ML) strategy has a great potential in accelerating processes of material research. In this study, accurate prediction of remanence in sintered NdFeB magnets has been achieved by a high-quality and few-shot dataset. We used a set of physical and chemical properties of element as inputs to build ML models based on element classification knowledge. Specifically, according to the position of elements, we divided them into three categories and then calculated the average properties of three positions separately. The strong generalization ability of best-performing ML model was further verified in nineteen unknown samples with only 0.724 % error. In addition, the symbolic regressor (SR) and SHapley Additive exPlanation (SHAP) algorithm were employed to explain the model results from physical perspective. In short, a high-efficiency and feasible ML strategy was developed for predicting remanence of sintered NdFeB magnets. We believe that this work will show great prospects in the composition design and performance screening of sintered NdFeB magnets. • The proper machine learning strategy for predicting remanence was developed. • Feature construction method was proposed based on element classification knowledge. • The generalization ability was confirmed in validation set with only 0.724 % error. • Clarifying how four key features affect remanence from physical insight. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties and the phase structure of Tb1− x Pr x Fe1.96 () were studied. It is found that the saturation magnetization on easy axis is decreased with increasing of Pr content, from 77.24Am2 kg−1 for , reduces to minimum value of 11.84Am2 kg−1 for , and returns to 37.14Am2 kg−1 for . The non-cubic phases appear beyond and the matrix changes from TbFe2 phase for to (Tb, Pr)Fe3 phase for , at last to (Tb, Pr)2Fe17 phase for . The compound structures turn more complex as the Pr content increased. [Copyright &y& Elsevier]

• The GBDP magnets were prepared by TbF 3 through screen printing technology. • The application of pressure can reduce diffusion time to develop core–shell structure. • The diffusion behavior and the role of F element in GBDP magnets were explored. The screen printing technology (SPT) was utilized to prepare TbF 3 coatings on Nd-Fe-B magnets. The effect of pressure-assisted grain boundary diffusion on magnetic properties and microstructure of Nd-Fe-B magnet has been intensively investigated. The results indicated that the intrinsic coercivity increment (ΔH ci) enhanced with increasing diffusion temperature and time. Meanwhile, the pressure could promote grain boundary diffusion process and shorten diffusion time obviously. Microstructural and compositional analyses indicated that the appropriate temperature and time were essential to develop the core–shell structure within a certain depth, which played a key role in the coercivity enhancement of magnet. Meanwhile, the thickness and continuity of Tb-rich shells decrease with diffusion depth. Furthermore, the pressure can strengthen the adhesion of TbF 3 coatings to base magnet, promoting the diffusion of Tb element into deeper regions and the formation of Tb-rich shells. The diffusion behavior and role of F element in magnet were also explored. The results confirmed that the diffusion depth of F was close to that of Tb element. However, the F element did not diffuse into 2:14:1 phase but formed NdOF phase distributing at grain boundaries. [ABSTRACT FROM AUTHOR]

The microstructure, magnetic and magnetostrictive properties as well as ultrasonic guided wave sensing performance of annealed Fe 81 Al 19 coatings prepared on 316L stainless steel by high velocity oxy-fuel spraying were investigated systematically. The maximum magnetostriction reaches 38 ppm with the coating annealed at 400 °C and the saturation magnetic field is <400 Oe. The phase transformation behavior of A2 → A2 + DO 3 occurs with the annealing temperature increases above 470 °C. Effects of annealing on texture and structural evolution and magnetic properties of the coating are also discussed. Based on magnetostrictive effect and Villari effect of Fe 81 Al 19 coating, the ultrasonic guided waves are actuated and detected successfully. With proper bias magnetic field, the amplitudes of echo signals can be enhanced in Fe-Al coating annealed at 500 °C. The corresponding (dλ/d H) max under a lower bias magnetic field indicates less eddy current loss and the optimal transduction. The deeper electromagnetic skin depth in the annealed coating results in a higher ultrasonic guided wave amplitude and improves the detection sensitivity in the electromagnetic acoustic transducers. This work exhibits the prospect of the magnetostrictive coatings in a range of potential applications, such as electromagnetic acoustical transducers used for non-destructive testing. Unlabelled Image • The magnetostrictive Fe 81 Al 19 coatings are fabricated by high velocity oxy-fuel spraying. • The phase transformation occurs at 470 °C during the post annealing temperature. • The maximum magnetostriction reaches 38 ppm in the annealed Fe 81 Al 19 coating. • Ultrasonic guided waves are obtained from magnetostrictive Fe-Al coating, which can be used in non-destructive testing. [ABSTRACT FROM AUTHOR]

Highlights • Coercivities of PCA, PTCA-5, PTCA-20 magnets are 19.6 kOe, 24.1 kOe and 24.3 kOe. • Coercivity enhancement of PCA magnet is owing to magnetic isolation by Nd-rich GBP. • Coercivity enhancement of PTCA-20 magnet results from magnetic hardening by TRS. • Magnetic isolation and hardening result in coercivity enhancement of PTCA-5 magnet. Abstract Grain boundary diffusion process (GBDP) with low melting-point alloy ribbons, namely Pr 70 Cu 15 Al 15 (PCA), Pr 65 Tb 5 Cu 15 Al 15 (PTCA-5) and Pr 50 Tb 20 Cu 15 Al 15 (PTCA-20, at%), was applied to Nd-Fe-B sintered magnet (52 M) as thick as 6 mm. The coercivities of diffused magnets by PCA, PTCA-5 and PTCA-20 increase significantly to 19.6 kOe, 24.1 kOe and 24.3 kOe, respectively, from original 14.7 kOe. Microstructural investigations indicate that the coercivity enhancement of PCA magnet is mainly attributed to magnetic isolation by continuous Nd-rich grain boundary phases (GBP). However, the coercivity enhancement of PTCA-20 magnet is mainly owing to magnetic hardening by Tb-rich shells (TRS), and that of PTCA-5 magnet results from a combined strengthening of magnetic isolation by GBP and magnetic hardening by TRS. Meanwhile, the coercivity of PTCA-5 magnet is as high as that of PTCA-20 magnet, but the former consumes Tb only 0.60 wt%, lower than 1.23 wt% for the latter. [ABSTRACT FROM AUTHOR]

Highlights • Tb-rich shells can be optimized by adjusting diffusion source, temperature and time. • Magnetic isolation is enhanced by forming continuous and smooth Nd-rich GBP. • Crystal structure of TJP and GBP transforms from hcp-Nd 2 O 3 to cubic-Nd 2 O 3. • Coercivity of magnet is greatly enhanced with efficient utilization of Tb. Abstract Effect of Tb content and diffusion parameters (diffusion temperature and time) on boundary structure and magnetic properties of Nd-Fe-B sintered magnet was systematically studied by grain boundary diffusion process (GBDP) using Pr 70− x Tb x Cu 15 Al 15 (x = 5, 10, 15, 20, atom fraction) alloys. When x increases from 5 at% to 15 at%, coercivities of diffused magnets increase from the original 11.9 kOe to 22.4 kOe for 5 at% magnet (PTCA-5) and 23.5 kOe for 15 at% magnet (PTCA-15), with a slight decrease in remanence. With x increasing to 20 at% (PTCA-20), coercivity of diffused magnet is only 0.6 kOe higher than that of PTCA-15 magnet, with sharp decrease in remanence. So, Tb content in Pr-Tb-Cu-Al alloy should be limited. And when diffusion temperature and time increase from 600 °C and 2 h to 950 °C and 8 h, coercivities of diffused magnet linearly increase first, and then reach stable. The enhancement mechanisms for magnetic properties contribute to magnetic hardening by Tb-rich shells, magnetic isolation by continuous Nd-rich grain boundary phases and reduced lattice misfit between Nd-rich phases and Nd 2 Fe 14 B grains. Furthermore, distribution of Tb-rich shells along diffusion length can be optimized by adjusting Tb content in diffusion sources and diffusion parameters, contributing to coercivity enhancement of magnet. [ABSTRACT FROM AUTHOR]

• Mn-Zn binary co-substituted cobalt ferrite (Co 1-x (MnZn) x Fe 2 O 4 (0 ≤ x ≤ 0.4)) was synthesized by conventionally compacting and magnetic field assisted injection molding. • Mn-Zn binary co-substitution changes the cation distribution in the crystal lattice and affects the magnetic properties of CoFe 2 O 4. • The existence of 〈0 0 1〉 silk texture in undoped oriented polycrystalline samples enhances strain sensitivity (dλ/dH) max (∼0.88 ppm/Oe) by ∼ 600 % of isotropic CoFe 2 O 4. Mn-Zn binary co-substituted cobalt ferrite (Co 1-x (MnZn) x Fe 2 O 4 (0 ≤ x ≤ 0.4)) was synthesized by conventionally compacting and magnetic field assisted injection molding. XRD and SEM analysis characterized the single-phase spinel structure, preferred 〈0 0 1〉 orientation, and uniform grain size. XPS analysis reveals the cation redistribution in the mixed spinel structure of co-substituted samples, which has a direct consequence on magnetic properties. The addition of Mn-Zn increases the saturation magnetization (M s), while decreases magnetocrystalline anisotropy constant (K 1), leading to a decrease of magnetostrictive saturation field (H S). For pressure samples, the maximum (dλ/dH) max is −0.15 ppm/Oe under 300 Oe applied field at x = 0.2. The samples with 〈0 0 1〉 fiber texture were prepared by magnetic field alignment of the semi-solid slurry to achieve higher magnetostrictive properties. The highest magnetostriction λ S reaches −432 ppm, which is 200 % higher than pressed samples, and the corresponding maximum strain derivative (dλ/dH) max reaches −0.88 ppm/Oe at a lower magnetic field. [ABSTRACT FROM AUTHOR]

The grain boundary diffusion process was applied to the commercial sintered Nd–Fe–B magnets using Pr 68 Cu 32 , Dy 70 Cu 30 and Pr 35 Dy 35 Cu 30 ribbons as direct diffusion source. The coercivities increased from 1114.4 kA/m for the original magnet to 1642.8 kA/m for the processed magnet by Pr 68 Cu 32 , higher than 1402.7 kA/m by Dy 70 Cu 30 . Microstructural investigations showed that the evident coercivity enhancement for the sample by Pr 68 Cu 32 was mainly attributed to continuous intergranular layers isolating Nd 2 Fe 14 B grains. Nevertheless, the coercivity enhancement of the sample by Dy 70 Cu 30 was mainly resulted from the magnetic strengthening of the extensive layers in Nd 2 Fe 14 B grains. [ABSTRACT FROM AUTHOR]

The surfaces parallel and perpendicular to c-axis of commercial N52 Nd-Fe-B magnet were coated with Tb by magnetron sputtering, respectively. The effect of Tb diffusion anisotropy on magnetic and mechanical properties was investigated. The coercivity increased from original 13.66 kOe to 21.90 kOe for the magnet diffusing parallel to c-axis and 19.68 kOe for the perpendicular diffusion, mainly resulting from the formation of (Nd, Tb) 2 Fe 14 B shells. The bending strength σ b of original magnet revealed obvious anisotropy. The σ b of diffused magnets for parallel to c-axis and perpendicular to c-axis showed a decrease by 1.76% and 6.14%, respectively. The deterioration in mechanical properties was related to internal stress resulting in transgranular fracture near surface of diffused magnet. The difference of magnetic and mechanical properties for the magnets with diverse diffusion direction was mainly caused by anisotropy of Tb diffusion in magnet. • Tb exhibits obvious anisotropy of diffusion behavior in Nd-Fe-B magnet. • The magnetic and mechanical properties of Tb-diffused magnets are anisotropic. • Internal stress and transgranular fracture near surface change mechanical properties. [ABSTRACT FROM AUTHOR]

In this work, iron-based soft magnetic composites coated with the amorphous SiO 2 layer have been fabricated by utilizing tetraethoxysilane in the reverse microemulsion method, and then the effects of addition amount of SiO 2 and annealing temperature on the magnetic properties were investigated. The results show that the surface of iron powders contains a thin amorphous SiO 2 insulation layer, which effectively decreases the magnetic loss of synthesized magnets. The magnetic loss of coated samples decreased by 87.8% as compared with that of uncoated samples at 150 kHz. Magnetic measurements show that the sample with 1.25 wt% SiO 2 has an acceptable real part and minimum imaginary part of permeability in comparison with other samples. Also, the annealing treatment increased the initial permeability, the maximum permeability and the magnetic induction and decreased the coercivity with increasing temperature in the range 300–600 °C. The results of the loss separation imply that the annealed SMCs have a higher hysteresis loss coefficient ( k 2 ) and lower eddy current loss coefficient ( k 3 ) as compared with the pure iron compacts after the same heat treatment due to the preservation of the SiO 2 layer. [ABSTRACT FROM AUTHOR]

In contrast to the disordered body-centered cubic (bcc) A2 phase, the ordered face-centered cubic (fcc) L1 2 phase exhibits negative magnetostriction (λ) and has a high elastic modulus (E). Therefore, an in-depth understanding of the microstructural evolution of Fe–Ga thin films from bcc A2 phase to fcc L1 2 phase is essential to obtain Fe–Ga thin films with desirable properties. The transformation of the phase structure, magnetic domain structure, and magnetic properties of Fe 72 Ga 28 thin films is analyzed in this study. The phase transformation of the Fe 72 Ga 28 thin film from A2 to A2 L1 2 occurred after heat treatment, as determined by high-resolution transmission electron microscopy (HRTEM) and glancing-incidence X-ray diffraction (GI-XRD). Non-continuous lattice distortion at the phase boundaries of A2 and L1 2 was also observed, as shown by geometric phase analysis (GPA) and electron backscattered scattering detection (EBSD). Numerous edge dislocations at the phase boundaries were revealed by HRTEM. A shift in the magnetic domain structure from the maze-like domain to maze-like domain and honeycomb-like domain was detected by magnetic force microscopy (MFM). The variation in magnetic properties was determined to be related to the structural transformation and ununiform lattice distortion between the phase boundaries of the A2 and L1 2. • The A2 to A2+L1 2 transition in annealed Fe 72 Ga 28 thin films is proved. • The largest lattice distortion is discontinuous along the phase boundaries of the A2 and L1 2 phases. • The lattice distortion of the L1 2 phase is not uniform, unlike that of the A2 phase. • Magnetic domain of annealed Fe 72 Ga 28 thin films changed from maze-like domain to maze-like domain and honeycomb-like domain. • The effects of structural transformation and lattice distortion on the magnetic properties of the films are evaluated. [ABSTRACT FROM AUTHOR]

• Nano-TiC particles can significantly improve the bending strength. • Nano-TiC particles are mainly distributed at the triple junction phase. • The complete lattice structure of the nano-TiC particle is maintained. Nano-TiC powder was introduced into sintered Nd-Fe-B magnets and the effect of adding content on mechanical and magnetic properties was investigated. The results show that the bending strength is significantly enhanced, showing an increase of approximately 28% for 0.6 wt% doping magnet compared to the Ref. sample without addition. Meanwhile, the coercivity and squareness degree are enhanced to a certain extent without obvious remanence reduction. Microstructural analysis shows that the nano-TiC particles mainly segregate at triple junction regions, which plays a key role in the enhancement of bending strength. [ABSTRACT FROM AUTHOR]

• Tb-rich shells is homogenized by substituting Al for Cu in Pr 60 Tb 10 Cu 30− x Al x alloys. • Magnetic decoupling of 2:14:1 phase is strengthened by increasing Al substitution. • Cu/Al co-addition can improve Tb diffusion efficiency by modifying boundary phase. • The highest value of H ci (kOe) + (BH) max (MGOe) is obtained by diffusing Pr 60 Tb 10 Cu 25 Al 5. Grain boundary diffusion process (GBDP) using Pr 60 Tb 10 Cu 30− x Al x (x = 0, 5, 15, 25, 30, atomic fraction) alloy ribbons, named as A0–A30 alloys, was applied to high maximum energy product (BH) max Nd-Fe-B sintered magnet. After diffusion, coercivity (H ci) of A0 magnet is significantly enhanced from the original 11.4 kOe to 19.5 kOe with remanence (B r) decreasing from 14.65 kGs to14.32 kGs, which is mainly attributed to magnetic hardening effect by Tb-rich shells. With substituting 5 at% Al for Cu, the H ci and B r of A5 magnet are simultaneously enhanced by the homogenized distribution of Tb-rich shells and the reduced interface energy of Nd-rich phase and Nd 2 Fe 14 B phase. The highest coercivity of 22.4 kOe is obtained for A25 magnet by further strengthening magnetic isolation of Nd 2 Fe 14 B phase, however, which results in a drastic decrease in B r due to the increased fraction of Nd-rich phase and too much substitution of Al for Fe in Nd 2 Fe 14 B phase. Therefore, the H ci (kOe) + (BH) max (MGOe) reaches to the peak value for A5 magnet. Also, it is proven that Cu/Al co-addition can effectively improve Tb diffusion efficiency by modifying intergranular Nd-rich phase. [ABSTRACT FROM AUTHOR]

• The orientation of the magnet is significantly increased by the wet pressing method with special double-layer mold. • The liquid solvents lubricate the powders well and are almost eliminated at the end of the pressing process. • The remanent magnetization of the magnet shows a significant increase with negligible coercivity change. • The density of magnet is greatly increased and approaches the limit one. • The compressive strength of the magnet is greatly improved compared with that of the traditional pressing method. Fine magnetic powder particles are usually utilized to prepare high coercivity Nd-Fe-B magnets. However, it is more difficult to obtain high orientation degree due to the larger friction between finer powder particles during magnetic-aligned compaction process, which greatly affects the performance of final magnets. In this work, a special wet pressing method is adopted to reduce the friction between the powder particles. The degree of alignment of the magnet is obviously increased and the microstructure is optimized. The remanent magnetization of the magnet shows a significant increase with negligible coercivity change, while the compressive strength is improved compared with that of the traditional method. [ABSTRACT FROM AUTHOR]