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Surface nitridation has been used to fabricate the insulation coatings of the Fe, FeSi, FeSiAl and FeSiCr soft magnetic composites (SMCs). Effects of the nitridation conditions on the magnetic performance of the SMCs have been investigated. Detailed growth mechanism and models of the coating layers for different alloy systems have been established based on combined thermodynamic and kinetics analysis. For Fe and FeSi SMCs, nitride coatings containing α-Fe(N) forms, while coexistenc of α-Fe(N) and Fe4N is obtained for the FeSiAl SMCs. For the FeSiCr system, the nitride coating is composed of α-Fe(N) and CrN with relatively large electrical resistivity, giving rise to enhanced magnetic performance compared with that of the SMCs prepared via traditional phosphoric acid passivation.

Three inorganic-organic hybrids have been designed by incorporating epoxy-modified silicone resin (ESR) with SiO2, Fe3O4 and their mixture in the application as the coating of Fe soft magnetic composites (SMCs). The introduced SiO2 nanoparticles are well dispersed in the ESR, while the Fe3O4 tends to agglomerate or even separate from the ESR. Simultaneous addition of the SiO2 and Fe3O4 gives rise to satisfactory distribution of both nanoparticles and optimized magnetic performance of the SMCs with high permeability (124.6) and low loss (807.8 mW/cm3). On one hand, introduction of the ferromagnetic Fe3O4 reduces the magnetic dilution effect, which is beneficial for improved magnetization and permeability. On the other hand, SiO2 incorporation prevents the agglomeration of the Fe3O4 nanoparticles and gives rise to increased electrical resistivity for reduced core loss as well as enhanced mechanical strength of the SMCs.

Hydrolysis precipitation as a new method was used in the preparation of oxide insulation matrix for FeSiAl soft magnetic composites (SMCs). The growth and composition of the matrix can be tuned by the concentration of the Al(NO3)3 solution, reaction temperature and pH value during the hydrolysis. With optimized Al(NO3)3 concentration of 0.6 mol/L and hydrolysis temperature of 75 °C, two mechanisms have been revealed in the formation of the insulation coating depending on the pH of the Al(NO3)3 solution. When pH = 3, the coating layer contains a mixture of Al2O3 and Fe2O3, while Al2O3 and SiO2 form as the coating for pH = 8. Despite that the Al2O3 dominates for both conditions, it grows via different routes. The Al(OH)3 as the precursor forms through Al3+ hydrolysis and heterogeneous nucleation for pH = 3. With increased pH to 8, the Al3+ directly reacts with OH− to form Al(OH)3 colloidal particles which adsorb onto the surface of FeSiAl powders via electrostatic attraction. Both mechanisms give rise to satisfactory magnetic performance with high effective permeability (μe = 103.5 and 113.4) and low core loss (Pcv = 278.4 mW·cm−3 and 237.8 mW·cm−3) for pH = 3 and 8 measured at 100 mT, 50 kHz.

MnZn power ferrites for MHz and wide temperature applications were prepared by ceramic process and effects of Co2O3 and MoO3 co-doping on the microstructure and magnetic properties have been investigated, and MnZn power ferrite with ultra-high cut-off frequency of 14.2 MHz has been prepared. It has been revealed that the grain size of the MnZn ferrite can be homogenize via the co-doping of Co2O3 and MoO3, giving rise to enhanced electrical resistivity, compensated magnetocrystalline anisotropy and reduced domain wall displacement. Effective reduction of the power loss with improved temperature stability and cut-off frequency have been achieved by synergistic function of Co2O3 and MoO3 via liquid-phase sintering increasing the possibility of Co2+ cation entering into the spinel lattice.

The phase composition, magnetic and microstructural properties of Nd 2 Fe 14 B/(α-Fe, Fe 3 B) nanocomposite magnets produced by injection casting technique have been studied. Magnetic hysteresis loop of the Nd 7 Y 6 Fe 61 B 22 Mo 4 permanent magnet demonstrates the coercivity as high as 1289 kA/m. Electron microscopy elucidates a microstructure composed of magnetically soft α-Fe, Fe 3 B and hard Nd 2 Fe 14 B/Y 2 Fe 14 B nanograins (20–50 nm) separated by ultra-thin grain boundary layer. The Henkel plot curve of the Nd 7 Y 6 Fe 61 B 22 Mo 4 magnet yields the existence of exchange coupling interactions between soft and hard phases. Macroscopically large size sheet magnet is obtained due to high glass forming ability of the Nd 7 Y 6 Fe 61 B 22 Mo 4 alloy derived from large atomic radius mismatch and negative enthalpy of alloy constituent elements. The high coercivity of the magnet is attributed to the magnetically hard phase increment, nucleation of reverse domains and the presence of thin grain boundary phase. Good magnetic properties such as remanence of 0.51 T, coercivity of 1289 kA/m and maximum energy product of 46.2 kJ/m 3 are obtained in directly casted Nd 7 Y 6 Fe 61 B 22 Mo 4 sheet magnets.

SnO 2 films exhibiting room temperature ferromagnetism (RTFM) have been prepared on Si (001) by pulsed laser deposition. The saturation magnetization (M s ) of the films experiences a decreasing trend followed by increasing with the growth temperature increased from RT to 400 ℃. The growth temperature affects both the concentration and the location of the oxygen vacancies as the origin of the RTFM. With lower growth temperatures ( O + ) in the inner film are the origin of the magnetism in SnO 2 films.

Forming Nd 2 Fe 14 B/(Nd, Dy) 2 Fe 14 B core–shell structure by intergranular adding Dy-containing sources into Nd–Fe–B sintered magnets is effective to improve coercivity and to minimize remanence loss simultaneously. However, the excessive Dy located in the intergranular regions has nearly no hard magnetic contribution, causing its low utilization efficiency. In this work, diluted Dy powders (Pr 37 Dy 30 Cu 33 )–H x were prepared and incorporated into Nd–Fe–B sintered magnets via a dual-alloy approach. The coercivity increases rapidly from 15.0 to 18.2 kOe by 21.3% with 2.0 wt% (Pr, Dy, Cu)–H x addition (the equivalent Dy is only 0.32 at%). The deduced coercivity incremental ratio is 10.0 kOe per unit Dy at%. Dehydrogenation reaction of (Pr, Dy, Cu)–H x occurs during sintering, which favors Dy diffusion towards the 2:14:1 phase grains as well as smoothing the grain boundaries (GBs). The enhanced local anisotropic field and the well decoupled 2:14:1 phase grains contribute to such rapid coercivity enhancement. This work suggests that adding diluted Dy hydrides is promising for fabricating high coercivity Nd–Fe–B sintered magnets with less heavy rare-earth consumption.

Fe soft magnetic composites (SMCs) with low core loss were fabricated via surface oxidation of the Fe powders by H2O and O2 at elevated temperatures. Surface oxidation prevents magnetic dilution due to the formation of the ferromagnetic iron oxide coating layer, giving rise to high magnetic flux density and effective permeability of the SMCs compared with those fabricated with traditional phosphate coating. Mechanism of the oxidation process has been investigated where Fe3O4 forms by reactions of Fe with H2O and O2. The Fe3O4 coating layer tends to convert into γ-Fe2O3 with increased oxidation temperature and time. By controlling composition of the coating layer, low core loss of 688.9 mW/cm3 (measured at 50 mT and 100 kHz) and higher effective permeability of 88.3 can be achieved for the Fe SMCs.

High coercivity Nd–Fe–B sintered magnets serving in high-temperature environments always consume expensive and scarce heavy rare-earth Dy, which has simulated considerable interest to reduce Dy usage. In this work, coercivity of Dy-free magnets was investigated through intergranular adding eutectic Ho 63.4 Fe 36.6 powders. The coercivity increases gradually up to 4 wt% Ho 63.4 Fe 36.6 addition, however the remanence starts to deteriorate drastically as the addition is over 2.5 wt%. Coercivity above 18.0 kOe is obtained at the expense of a slight reduction in remanence through optimizing the addition amount and sintering conditions. The coercivity enhancement is explained through microstructural observations and elemental distribution analysis. (i) (Nd, Ho) 2 Fe 14 B shell forms in the outer region of 2:14:1 phase grains, strengthening the local magnetic anisotropy filed, (ii) RE-rich grain boundary phase with low Fe content is thickened, weakening the magnetic coupling between adjacent 2:14:1 phase grains, and (iii) 2:14:1 phase grains are refined upon lowering sintering temperature, reducing the microstructural defects and the stray fields aroused from neighboring grains.

Here we report that Nd-Fe-B sintered magnets containing only 12.6–12.9 at.% rare earth elements exhibit maximum energy product (BH)max of 48.0–48.8 MGOe, remanence Br of 1.40–1.41 T, and coercivity Hcj of 12.2–14.5 kOe, which are prepared through introducing eutectic Dy71.5Fe28.5 (at.%) into the near-stoichiometric (Pr,Nd)12.3FebalB6.1 (2:14:1 phase, at.%) magnets via grain boundary restructuring (GBR) approach. The low-melting-point Dy71.5Fe28.5 additive facilitates the liquid phase sintering process to achieve high densification, and generates continuous grain boundary layers that well isolate the main phase grains. Moreover, Dy enrichment at the surface region rather than the center of 2:14:1 grains not only increases the coercivity by enhancing the local magnetocrystalline anisotropy field, but also maintains the remanence. The fact that total rare earth contents of Dy71.5Fe28.5-restructured magnets are much lower than those commercial ones with equivalent magnetic performance (usually 13.5–14.0 at.%) delights the prospective future of GBR approach on fabricating high-performance Nd-Fe-B.

Here we report the synergistic effects of Zr and Dy71.5Fe28.5 (at%) co-addition on the magnetic performance of Nd-Fe-B sintered magnets and the underlying mechanism. The high-melting-point Zr suppresses the abnormal grain growth during high-temperature sintering process and also causes insufficient densification as limited by its poor wettability with the main phase grains. The co-addition of low-melting-point Dy71.5Fe28.5, however, increases the volume fraction of liquid intergranular phases upon sintering, and facilitates the formation of smooth and continuous grain boundaries, which can counteract the adverse effect of single Zr addition. As a result, the 2:14:1 main phase grains are well isolated, exhibiting an effectively weakened short-range exchange coupling between adjacent grains. Moreover, Dy diffusion towards the surface region of grains also generates a (Pr, Nd, Dy)2Fe14B magnetically hardening outer layer. Owing to the joint contributions from grain refinement, optimized grain boundary layer, and Dy-enriched hardening shell, the coercivity can be significantly enhanced from 14.0 to 21.9 kOe upon co-doping 0.3 wt% Zr and 3 wt% Dy71.5Fe28.5, accompanied with a slight remanence reduction. It demonstrates that co-doping low-melting-point and high-melting-point additives provides an efficient approach to fabricate high-performance Nd-Fe-B magnets.

Multi-main-phase (MMP) magnets prepared by co-sintering Nd2Fe14B and (Nd,Ce)2Fe14B powders have shown better magnetic properties than the single-main-phase (SMP) magnets with the same average composition, enabling the preparation of high cost-performance permanent magnets with high Ce content. The present work focuses on the squareness factor (Q) of demagnetization curve for MMP Nd-Ce-Fe-B magnets, which represents the magnetic stability in practical applications. It is found that the MMP magnets prepared with larger fraction of (Nd,Ce)2Fe14B components possess higher Q value than those with lower fraction, which highlights the importance of relative fraction between the magnetically softer Ce-rich and the magnetically harder Nd-rich 2:14:1 grains on the squareness for the MMP magnets. Besides, the reduced Ce/Nd gradients within 2:14:1 grains and the formation of continuous RE-rich (RE, rare earth) grain boundaries also make contributions to the recovered squareness factor as well as the sustained coercivity.

Intermetallic compounds of Gd with Si, Ge, and Sn near 1:2 stoichiometry adopt several closely related crystal structures. We find that GdSi1.78 and Gd(Si0.684Ge0.316)1.78 crystallize in the same GdSi1.4-type orthorhombic structure (space group Imma), while GdGe1.57 and GdSn2 adopt α-ThSi2-type tetragonal structure (space group I41/amd) and ZrSi2-type orthorhombic structure (space group Cmcm), respectively. All compounds order antiferromagnetically; their Neel temperatures are only weakly affected by the magnetic field of less than 50 kOe. Unusual features are observed including multiple phase transitions and thermomagnetic irreversibilities.

To satisfy high-temperature applications, heavy rare-earth (RE) Dy is commonly introduced into the Nd–Fe–B sintered magnets to improve the coercivity. In addition to forming (Nd, Dy)2Fe14B, Dy also exists in the intergranular RE-rich phase. Hence, understanding the effect of Dy on the electrochemical characteristics of the RE-rich phase and corrosion resistance of the magnet is of importance. In this work, eutectic alloy Dy71.5Fe28.5 powders were added into the (Pr0.2Nd0.8)12.3FebalB6.1 magnet through binary-alloy approach to investigate the corrosion resistance of the magnet in electrochemical and hot/humid environments. The results demonstrate that Dy is enriched in the intergranular phase, improving its electrode potential and stability due to the higher electrode potential of Dy than Nd or Pr. As a consequence, the electrode potential difference between the 2:14:1 phase and the RE-rich phase is reduced, improving the corrosion resistance. Furthermore, formation of (Pr, Nd, Dy)2Fe14B shell with stronger local anisotropy surrounding the 2:14:1 phase grains improves the coercivity with a slight remanence loss. Therefore, intergranular adding Dy–Fe alloy powders can obtain both high magnetic properties and good corrosion resistance simultaneously.

Fe–Si–Ni powders were firstly prepared into soft magnetic composites (SMCs) by ball milling, surface passivation and subsequent compaction. The morphology, phase composition, and magnetic properties of the Fe–Si–Ni powders and their high-frequency performance as SMCs were investigated. The Fe–Si–Ni powders, with saturation magnetization (Ms) of 254.40 emu/g after annealing, were milled down to particle sizes ranging from 40 μm to 150 μm. Surface passivation of the powders was carried out with 0.2–1.0 wt% phosphoric acid solution prior to compaction. Evolution of the high-frequency properties for the Fe–Si–Ni SMCs with the passivator concentration and the molding pressure was studied. With optimized preparation parameters, high saturation flux density (Bs) of 1.23 T, stable permeability, and superior dc-bias property with a percentage permeability above 70% while H=50 Oe were achieved for the Fe–Si–Ni SMC. Minimum core loss (285 mW/cm3) was also measured at 50 kHz for Bm=50 mT.

Magnetic performance of Nd–Fe–B sintered magnets, especially the coercivity is highly sensitive to microstructures extrinsically. To enhance coercivity of the near-stoichiometric Nd 2 Fe 14 B magnet (Nd, Pr) 12.5 Fe bal B 6.1 (at%), the microstructure is optimized by varying sintering condition. At lower sintering temperatures, full densification cannot be reached even prolonging the sintering time, the coupling between adjacent 2:14:1 phase grains results in a low coercivity. At higher sintering temperatures, the grains of 2:14:1 phase grow up quickly, also deteriorating the coercivity. At an optimum sintering temperature of 1050 °C, the magnet reaches a full densification with most 2:14:1 phase grains of 4–5 μm, showing a high coercivity of 16.4 kOe. The formation of smooth and continuous grain boundary RE-rich phase reduces the magnetic interactions and the grain refinement hinders nucleation of reversed domains at low fields, respectively.

Aiming to improve the corrosion resistance of Nd–Fe–B sintered magnets, Nd 6 Co 13 Cu powders are introduced into a near-stoichiometric Nd 2 Fe 14 B magnet by grain boundary restructuring. The restructured magnet containing only 28.46 wt% (Pr, Nd) shows much better corrosion resistance against hot/humid, acidic and saline environments than the un-restructured magnet with equivalent rare earth content (REC). It results mainly from the formation of higher electrode potential Co-rich phase and Cu-rich interface layers in the intergranular regions. Besides, magnetic properties of the restructured magnet are well retained with coercivity H cj above 12.5 kOe, remanence B r above 14.0 kGs and maximum magnetic energy product ( BH ) max above 48.5 MGOe respectively. It can be ascribed to the formation of more continuous grain boundary phase that isolates well the neighboring Nd 2 Fe 14 B grains.

The magnetic properties, phase evolution and microstructure of Fe70−xMxB19Nd7Nb4 (M=Si, Gd, Si+Gd; x=0–2.5 at%) bulk nanocomposite permanent magnets in the form of rods produced by annealing the amorphous precursor have been investigated systematically. Microstructural examination, three-dimensional atom probe microanalysis, δM-plots, X-ray diffraction analysis and magnetometer studies deduced that good magnetic properties in the magnets originate from the homogenous microstructure consisting of exchange coupled, soft magnetic (α-Fe, Fe3B) and hard magnetic (Nd,Gd)2Fe14B nanophases. Optimally annealed Fe70B19Nd7Nb4 rod magnets exhibit magnetic properties of Br=0.61 T, iHc=876 kA/m and (BH)max=50.2 kJ/m3. Gadolinium and silicon addition to quaternary Fe70B19Nd7Nb4 alloy increased the mass fraction of hard magnetic phase, strengthened the exchange coupling interactions and enhanced the magnetic properties. Gadolinium and silicon segregated into hard magnetic phase which led to enhance coercivity up to 1115 kA/m. Enhancement in the coercivity is mainly resulted by hard phase increment as well as domain wall pinning, while strengthening of exchange coupling is caused by grain size refinement and increase in Curie temperature of the magnetic phases. The Fe67B19Nd7Gd2Nb4Si1 magnetic rods of 1.2 mm in diameter demonstrated the best magnetic properties such as intrinsic coercivity, iHc of 1115 kA/m, remanence, Br of 0.57 T and maximum energy product, (BH)max of 65.7 kJ/m3.

To enhance coercivity and reduce the rare-earth consumption of Nd–Fe–B sintered magnets simultaneously, low melting point Dy 69 Ni 31 (at%) powders are introduced into a slightly off-stoichiometric Nd 2 Fe 14 B (2:14:1 phase) (Pr, Nd) 12.36 Fe bal B 6.09 (at%) starting magnet. Because of insufficient rare-earth element, the starting magnet possesses discontinuous intergranular grain boundaries (GBs) that cannot decouple the 2:14:1 phase grains well, hence leading to a low coercivity of only 9.53 kOe. The Dy 69 Ni 31 additive provides extra rare-earth that improves the liquid-phase sintering with the formation of continuous intergranular GBs, accompanied by the diffusion of Dy towards surface region of the 2:14:1 phase grains. A significant increment in coercivity of 6.25 kOe is realized with a slight reduction in remanence by −3.0% per unit at% Dy. Satisfactory magnetic performance with ( BH ) max =47.49 MGOe, B r =13.92 kGs and H cj =13.93 kOe, is obtained in the magnet containing only 12.92 at% rare-earth elements, in which 0.68 at% Dy is included. It combines advantages of the modification of intergranular GBs and the formation of a magnetically hardening shell surrounding 2:14:1 phase grains, which can be a promising approach to fabricate low rare-earth and high performance Nd–Fe–B magnets for mass production.

To improve coercivity without sacrificing other magnetic performance of NdFeB sintered magnets, a low melting point Dy32.5Fe62Cu5.5 alloy was introduced as an intergranular additive. Magnetic properties and microstructure of the magnets with different Dy32.5Fe62Cu5.5 contents were studied. At the optimum addition of 3 wt%, coercivity Hcj was enhanced from 12.7 to 15.2 kOe, the maximum magnetic energy product (BH)max was simultaneously increased from 46.6 to 47.8 MG Oe, accompanied by a slight reduction in remanence Br. Further investigation on microstructure and grain boundary composition indicated that the enhanced Hcj and (BH)max could be attributed to the refined and uniform 2:14:1 phase grains, continuous grain boundaries and a (Nd,Dy)2Fe14B hardening shell surrounding the 2:14:1 phase grains.

Nd 7 Fe 67 B 22 Mo 3 Zr 1 magnets in rods have been prepared by annealing the amorphous precursors produced through injection casting. Phase formation, microstructure and magnetic properties of Nd 7 Fe 67 B 22 Mo 3 Zr 1 magnets have been investigated and discussed in the as-cast and annealed states. Cast Nd 7 Fe 67 B 22 Mo 3 Zr 1 rods have the soft magnetic characteristics, which changed into magnetically hard by annealing. Magnetic properties in Nd 7 Fe 67 B 22 Mo 3 Zr 1 magnets are influenced by the intrinsic properties of magnetically soft α-Fe (Fe 3 B) and hard Nd 2 Fe 14 B phases. The Zr and Mo elements in the Nd 7 Fe 67 B 22 Mo 3 Zr 1 alloy promote the formation of amorphous phase and reduce the grain size of magnetic phases. Optimal annealed Nd 7 Fe 67 B 22 Mo 3 Zr 1 rods of 2 mm in diameter and 52 mm in length presented maximum magnetic properties such as: remanence ( B r ) of 0.53 T, coercivity ( i H c ) of 1110 kA/m and maximum energy product ( BH ) max of 49.5 kJ/m 3 .

Intergranular adding Dy-containing powders is effective to enhance the coercivity of Nd2Fe14B-based sintered magnets with slight remanence loss due to the formation of (Nd, Dy)2Fe14B hardening shell surrounding the 2:14:1 grains. Here, the influences of post-sinter annealing (PSA) time on microstructure and coercivity of Dy69Ni31-added Nd-Fe-B magnets have been investigated. With prolonging the annealing time at 580 °C, the coercivity increases rapidly from 10.1 kOe to 16.2 kOe when the annealing time is less than 6 h and keeps nearly unchanged after longer time annealing. Longer time annealing promotes the formation of thicker Dy-enriched 2:14:1 hardening shells as well as optimized and continuous grain boundary (GB) layers, which plays positive contributions to enhance coercivity. However, the transmission electron microscope (TEM) investigations reveal that crystal structure of RE-oxides at the triple junctions changes with prolonging PSA time, transforming from double hexagonal close-packed (d-hcp) to a mixture of face-centered cubic (fcc) and ordered body-centered cubic (bcc) and to hexagonal close-packed (hcp). The latter transformation may play a negative role on coercivity enhancement, offsetting the positive contributions. These findings may provide a useful guide for engineering the microstructure of Nd-Fe-B sintered magnets.

Fe69B20.2Nd4.2Nb3.3Y2.5Zr0.8 hard magnets in rods were produced by injection casting method. Magnetic properties, phase evolution and microstructure for Fe69B20.2Nd4.2Nb3.3Y2.5Zr0.8 magnets have been investigated and presented in as-cast and annealed states. The magnets possess soft magnetic characteristics in as-cast state, and hard magnetic characteristics after annealing. The Nb refines the grain sizes of α-Fe, Fe3B and Nd2Fe14B magnetic phases, while Y and Zr improve the glass forming ability. Good magnetic properties in Fe69B20.2Nd4.2Nb3.3Y2.5Zr0.8 magnets arise from the microstructure composed of magnetically exchange coupled nanocrystalline α-Fe, Fe3B and Nd2Fe14B phases. Optimal annealed magnets of 2 mm diameter and 30 mm length demonstrate the hard magnetic properties, i.e. intrinsic coercivity jHc of 496 kA/m, remanence Br of 0.76 T and maximum energy product (BH)max of 72.0 kJ/m3.

Magnetic phase evolution, crystallographic texture, microstructure and magnetic properties of Fe–28Cr–15Co–3.5Mo–1.8Ti alloy have been investigated by X-ray diffractometry, scanning transmission electron microscopy and magnetometry techniques as a function of processing conditions. Heat treatment conditions for obtaining optimum textural, microstructural and magnetic properties have been established by the experimentations. The Goss {110}〈001〉 and cube type {001}〈010〉 textures have been developed in an optimal treated Fe–28Cr–15Co–3.5Mo–1.8Ti magnets. The coercive force in Fe–28Cr–15Co–3.5Mo–1.8Ti magnets depends critically on the shape anisotropy of rod-like Fe Co Ti-rich α 1 particles and remanence on the alignment and elongation of α 1 particles parallel to applied magnetic field 〈100〉 directions. The optimum magnetic properties obtained in Fe–28Cr–15Co–3.5Mo–1.8Ti alloy are intrinsic coercive force, i H c , of 78.8 kA/m (990 Oe), remanence, B r of 1.12 T (11.2 kG) and energy product, (BH) max of 52.5 kJ/m 3 (6.5 MGOe). The development of Fe–28Cr–15Co–3.5Mo–1.8Ti magnets as well as characterization of texture, microstructural and magnetic properties in the current study would be helpful in designing the new Fe–Cr–Co–Mo based magnets suitable for scientific and technological applications.

The Fe 63 B 23 Nd 7 Y 3 Nb 3 Cr 1 nanocomposite magnets in the form of sheets have been prepared by copper mold casting technique. The phase evolution, crystal structure, microstructural and magnetic properties have been investigated in the as-cast and annealed states. The as-cast sheets show magnetically soft behaviors which become magnetically hard by thermal annealing. The optimal annealed microstructure was composed of nanosize soft magnetic α-Fe (19–29 nm) and hard magnetic Nd 2 Fe 14 B (45–55 nm) grains. The best hard magnetic properties such as intrinsic coercivity, j H c of 1119 kA/m, remanence, B r of 0.44 T, magnetic induction to saturation magnetization ratio, M r / M s =0.61 and maximum energy product, (BH) max of 55 kJ/m 3 was obtained after annealing at 680 °C for 15 min. The annealing treatment above 680 °C results in non-ideal phase grains growth, which degrade the magnetic properties.

The Fe65B22Nd9Mo4 nanocomposite permanent magnets in the form of a rectangular cross sectioned rod have been prepared by annealing the amorphous precursors. The thermal behavior, structure and magnetic properties of the magnets have been investigated by differential scanning calorimetry, X-ray diffractometry, electron microscopy and magnetometry techniques. The as-cast Fe65B22Nd9Mo4 alloy showed soft magnetic properties, which changed into magnetically hard after annealing. Results provoke that the magnetic properties of the alloy are sensitive to thermal processing conditions. The optimum hard magnetic properties with a remanence (Br) of 0.56 T, coercivity (iHc) of 920.7 kA/m and maximum energy product (BH)max of 50.15 kJ/m3 were achieved after annealing the alloy at 983 K for 10 min. The good magnetic properties of Fe65B22Nd9Mo4 magnets are ascribed to the exchange coupling between the nano-scaled soft α-Fe, Fe3B and hard Nd2Fe14B magnetic grains.

The microstructural and magnetic properties of Al 100− x Cu x (15at%≤ x ≤45 at%) doped Nd–Fe–B magnets were studied. The distribution and alloying effects of Cu or Al on the intergranular microstructure were investigated by thermodynamic analysis, differential scanning calorimetery and microscopy techniques. It was observed that when the Cu content of Al 100 x Cu x exceeds to 25 at%, the (Pr, Nd)Cu and CuAl 2 phases form in these magnets. The formation of (Pr, Nd)Cu phase depends on the negative formation enthalpy of (Pr, Nd)Cu and the exclusive distribution of Cu in the intergranular regions. The eutectic reaction between (Pr, Nd)Cu phase and (Pr, Nd) occurs at 480 °C, which forms the liquid phase that dissolves the (Pr, Nd) 2 Fe 14 B surface irregularities and thus increases the quantities of (Pr, Nd)-rich phase at the grain boundaries. These changes benefit the grain boundary microstructure, especially the distribution of (Pr, Nd)-rich phase, which effectively improves the intrinsic coercivity i H c due to the decreases of exchange coupling between the (Pr, Nd) 2 Fe 14 B grains.

In this work, we have investigated the room-temperature phase constitution of heat-treated Fe 81 Ga 19 alloys cooled from 800 °C at different rates. Results show that at cooling rates in the range from 0.43 to 0.26 °C/min, in addition to the A2 matrix, an fcc phase also can be observed in Fe 81 Ga 19 samples at room temperature. To investigate the precipitation of the fcc phase out of A2 matrix, a systematic study of phase constitution was carried out on the samples quenched from different temperatures during cooling from 800 °C at 0.32 °C/min, which reveals an anomalous phase transformation between A2 and fcc. Precipitation of the fcc phase from A2 matrix occurs at 500 °C and its volume fraction exhibits a sharp increase at 400 °C. However, it begins to dissolve when further decreasing the temperature and only a minor fcc phase can be retained at room temperature, which suggests that the fcc phase is metastable below 400 °C. Magnetic measurements indicate that the precipitation of fcc phase deteriorates the saturation magnetization of Fe 81 Ga 19 .

A 〈1 1 0〉 oriented rod of the alloy Tb 0.3 Dy 0.7 Fe 1.95 was subjected to a magnetic heat treatment, cooling through its Curie temperature under 240 kA/m. Besides the improved magnetostriction under free conditions, the magnetically annealed rod still exhibited an obvious magnetostriction “jump” effect when subjected to a uniaxial compressive pre-stress. A giant magnetostriction of 2680×10 −6 was achieved under 640 kA/m and 30 MPa, which became 67% larger than before magnetic annealing. The optimum magnetostrictive strain coefficient d 33 was also dramatically enhanced. Magnetic force microscopy images show magnetic domain configurations that contribute to the improved magnetostrictive performance. The effect of induced additional anisotropy by magnetic annealing on the improvement of the magnetostriction is also discussed.

Nanocrystalline Fe–Ti–Si–Al flaky powders with large aspect ratio have been fabricated by high-energy planetary milling melt-spun ribbons. Magnetic composites made of thermally annealed Fe–Ti–Si–Al flaky powders embedded in epoxy resin exhibit excellent electromagnetic wave absorption properties in a wide frequency range from 100 MHz to 2.65 GHz. Ti additions can enhance the electrical resistivity of Fe–Si–Al alloy without changing the crystallographic structure, resulting in the reduction of eddy current loss at high frequencies. Moreover, the substitution of Ti for Fe enhances the cut-off frequency of flaky powder–polymer composites. Meanwhile, compared to the Ti-free composites, reflection loss of the Ti-doped composites (3 mm in thickness) is lower than −10 dB in the frequency range from 593 MHz to 1.83 GHz, indicating that the composites can effectively work in a wider frequency bandwidth.

This work presents a study on the relation between the fiber texture and the magnetostrictive performance in an antiferromagnetic Mn 50 Fe 50 alloy wire, which was prepared through the combining process of hot rolling and cold drawing. The face-centered cubic (fcc) crystal structure can be retained during the plastic deformation process. Mixed fiber textures consisting of both 〈1 1 0〉 and 〈1 0 0〉 components were formed along the drawing direction (DD) in the wire. A large magnetostriction of 750 ppm was obtained along DD under 1.2 T, which can be ascribed to the single γ phase and the formation of preferred crystal orientation.

Distributions of particles in a suspension comprised of magnetic particles (MPs) and nonmagnetic particles (NPs) under gradient magnetic fields are vitally important for the preparation of magnetic–nonmagnetic functionally graded materials (FGMs). In the present study, the effects of magnetic field gradient, magnetic interaction between MPs and concentration of NPs on the distributions of particles in the suspension are investigated using a two-dimensional Monte Carlo simulation. The results show that a gradient distribution of MPs is formed under gradient magnetic fields and increases with increasing the field gradient. However, as the interaction between MPs increases, the distribution gradient decreases, accompanied by the formation of chain-like MP clusters. Moreover, NPs are found to hinder the translation of MPs along the field direction. As the NP concentration increases, the translation of MPs becomes difficult.

The structures of suspensions comprised of magnetic and nonmagnetic particles in magnetic fields are studied using two-dimensional Monte Carlo simulations. The magnetic interaction among magnetic particles, magnetic field strength, and concentrations of both magnetic and nonmagnetic particles are considered as key influencing factors in the present work. The results show that chain-like clusters of magnetic particles are formed along the field direction. The size of the clusters increases with increasing magnetic interaction between magnetic particles, while it keeps nearly unchanged as the field strength increases. As the concentration of magnetic particles increases, both the number and size of the clusters increase. Moreover, nonmagnetic particles are found to hinder the migration of magnetic ones. As the concentration of nonmagnetic particles increases, the hindrance on migration of magnetic particles is enhanced.

To improve the magnetic properties and corrosion resistance of magnet, SiO 2 nanopowders were added into Nd 28.25 Dy 2.75 Fe bal Al 0.15 Ga 0.1 Nb 0.1 B 0.98 -sintered magnets as grain boundary modifiers. It was found that the intrinsic coercivity ( H cj ), remanence ( B r ) and corrosion resistance were all improved with addition of certain amount of SiO 2 nanopowders. The optimum addition amount of SiO 2 nanopowders was found to be 0.01 wt%. Thermodynamic calculation in combination of energy dispersive X-ray spectroscopy (EDX) analyses indicated that SiO 2 nanopowders reacted with Nd of Nd-rich phase. As a result, the intergranular phase was modified, and the grain growth of main phase was restrained. It led to the optimization of microstructure.

Crystal structure and magnetic properties of magnetostrictive compounds Tb0.36Dy0.64(Fe0.85Co0.15)2−xBx (0⩽x⩽0.15) have been investigated at room temperature. The matrix of these compounds keeps a cubic MgCu2-type structure. Lattice parameter a of the Laves phase decreases to reach a minimum at x=0.10, then increases with increasing boron content. Through analyzing the Mossbauer spectra, the easy magnetization direction (EMD) for all samples is confirmed to lie along 〈111〉 direction at room temperature, suggesting the presence of the giant magnetostriction. The mean hyperfine field Hhf and the deduced iron moment μFe increase with increasing boron content, resulting in the enhancement of both Curie temperature TC and spin reorientation temperature Tr. Although the addition of B enlarges the magnetocrystalline anisotropy constant K1, the composition dependence of the ratio λ/K1 for Tb0.36Dy0.64(Fe0.85Co0.15)2−xBx, however, reaches a maximum value at x=0. 05 under high magnetic fields.

To improve sintered NdFeB magnets’ thermal stability and magnetic properties, combined addition of elements Cu and Gd was investigated. It was found that with Gd addition increase to 1.0%, the temperature coefficient α improved from −0.15 to −0.05%/°C (maximum working temperature 120 °C), but the remanence and the maximum energy product linearly decreased. With addition of Cu in Gd-containing magnets the intrinsic coercivity increased greatly, and the remanence increased also because of their density improvement, and optimum Cu content was achieved at 0.2%. Microstructure analysis showed that most of the Cu distributed at grain boundaries and led to clear and smooth morphologies. Magnets with high thermal stability α=−0.05%/°C and magnetic properties were obtained with addition of Gd=0.8% and Cu=0.2%.

Nanocomposite (Nd,Pr) 2 Fe 14 B/α-Fe magnets were prepared by crystallizing the amorphous melt-spun ribbons. The effects of Nb and Zr additions on the crystallization behavior, microstructure, and magnetic properties of (Nd 0.4 Pr 0.6 ) 8.5 Fe 85.5− x − y Nb x Zr y B 6 ( x = 0 , 0.5 , 1 ; y = 0 , 0.5 , 1 ) alloys were studied. The microstructure and phase analysis shows that for (Nb,Zr)-free ribbons, α-Fe first precipitates, followed by the crystallization from amorphous to metastable phase before final transformation to the 2 : 14 : 1 phase and α-Fe. However, the combined Nb and Zr additions can increase the precipitating temperature of α-Fe, restrain the formation and growth of α-Fe, avoid the formation of metastable phase, refine and uniform the grain size, and thus greatly enhance intergrain exchange coupling between the hard and soft magnetic phases (verified by δM – H plot). After optimal thermal treatment, the coercivity and maximum energy product increase from 411 kA/m, 107 kJ/m 3 for (Nd 0.4 Pr 0.6 ) 8.5 Fe 85.5 B 6 sample to 534 kA/m, 144 kJ/m 3 for (Nd 0.4 Pr 0.6 ) 8.5 Fe 84.5 Zr 0.5 Nb 0.5 B 6 sample, respectively.

The effects of CuO and V2O5 additions and the particle sizes of precursor materials on the microstructure and relative initial permeability of low firing temperature NiCuZn ferrites were investigated. It was found that additions of CuO and V2O5 contribute to the grain growth and densification of matrix in the sintering process, which were favorable for increase in relative initial permeability. The relative initial permeability was also strongly affected by the average particle size of precursor materials. Through using precursor materials of 0.8 μm average particle size and adding 10 mol% CuO and 0.20 mol% V2O5, for the low firing temperature NiCuZn ferrite, very high relative initial permeability of 1417 can be achieved at the frequency of 1 MHz.

The effect of annealing treatment on the magnetic properties and microstructure of Nd 12.0 Dy 2.8 Fe 74.7 Co 3.4 Cu 0.2 B 6.9 magnets has been investigated. It is found that intrinsic coercivity i H c is improved with the increase of annealing temperature, and the maximum value is attained at 480 °C. i H c is rapidly decreased with a further increase of annealing temperature. For a given annealing temperature of 480 °C, i H c is increased with the increase of annealing time, and the maximum value is achieved at 2 h. It almost remains constant when annealing time is further increased. However, while the annealing treatment has little effect on remanence B r . It is certain that the increase of i H c for the annealed magnets arises from the more smooth grain boundaries of the RE 2 Fe 14 B phases and the more continuous/uniform distribution of RE-rich phases. The great change of microstructure in the annealed magnets can be explained using atomic diffusion theory.

Dy and Nb were added into the sintered NdFeB magnets with the aim of improving their magnetic properties and corrosion resistance. It was found that intrinsic coercivity of magnets is promoted whilst remanence is reduced as a result of Dy addition. Simultaneous addition of Dy and Nb not only gives rise to greatly improved coercivity, but also suppresses the undesirable effect of Dy on the remanence. The optimum magnetic properties were achieved when 1.0% Dy and 1.5% Nb were incorporated. Moreover, corrosion resistance of NdFeB magnets improves with the increase in the content of Dy and Nb.