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Metacomposite absorbers could be optimized either by the magnetic and dielectric properties of absorbents or by periodically arranged structural units at macroscopic scale. Herein, high-performance microwave absorption Ni@C nanocapsules synthesized by a modified arc-discharge method were mixed with polyvinyl acetate adhesive and then formed a periodic millimetric pattern on a polyethylene terephthalate substrate. Such a metacomposite structure results in a significant tunability and enhancement for the microwave absorption, associated with the maximum absorption of structured absorbers presenting 52.34% absorption efficiency higher than 29.20% of the non-structured absorber. In particular, it is demonstrated that the anisotropic absorption resonances can be tuned by changing the rotation angle of multi-layered assembly. This enhanced absorption is well explained by theoretical simulation, owning to the millimeter “capacitor-like” dielectric couplings between the microstructural units. The present study thus shows an alternative way to design tunable metacomposite absorbers.

Magnetostriction deterioration has been observed in slowly cooled Fe-Ga alloys when compared with the high temperature quenched ones. To reveal the underlying origin, here we investigated the microstructure of Fe81Ga19 thin-sheet samples quenched after slow cooling (at ∼0.3 K/min) to near and below the decomposition phase boundary between A2 and (A2’ + L12) phases. In comparison with the sample quenched at 1273 K (much higher than the decomposition phase boundary, ∼793 K) or the one quenched near the decomposition boundary (773 K), magnetostriction deterioration is observed for the one quenched below the decomposition boundary (673 K). Besides the A2 matrix phase, quenching at 673 K also promotes the formation of secondary L12 phase with negative magnetostriction and the phase transformation induced dislocations located close to the grain boundaries. Simultaneously, weak D03 ordering of the untransformed bcc matrix is also observed. All these microstructural changes deteriorate the magnetostriction. Our work provides important information why the magnetostriction of Fe81Ga19 greatly depends on the thermal history.

Y-Ce co-substituted RE-Fe-B (RE, rare earth) sintered magnets with good thermal stability have attracted growing attention as low-cost hard magnetic materials. The inferior intrinsic properties of Y2Fe14B and Ce2Fe14B to Nd2Fe14B, however, limit the substitution of Y-Ce for Nd at a low level. In this work, (Nd, Pr)-Hx powders are introduced into (Nd, Pr)22.8(Y, Ce)7.7FebalM1.3B1.0 sintered magnets to further enhance the coercivity. By incorporating 1 wt% (Nd, Pr)-Hx, the coercivity is increased to 9.7 kOe, which is 16.9% higher than that for the starting magnet (8.3 kOe). Continually increasing (Nd, Pr)-Hx addition to 2 and 3 wt% lead to a very limited coercivity increment, i.e. to 10.0 kOe and 10.3 kOe, respectively. The formation of continuous RE-rich intergranular phase by the extra Nd/Pr after (Nd, Pr)-Hx dehydrogenation can enhance the magnetic isolation effect between adjacent matrix phase grains, resulting in coercivity enhancement. However, more Nd atoms exist in the RE-rich phase rather than form the Nd-rich hardening shell, which is distinct from the available Nd-Ce-Fe-B system. The REs distribution within the matrix phase grain is similar before and after (Nd, Pr)-Hx incorporation for the Nd-Ce-Y-Fe-B system. It is deemed that the preferential occupancy of Y in the 2:14:1 matrix phase hinders the diffusion of Nd into the outer layer of Y-Ce enriched regions, being responsible for the limited coercivity increment with higher (Nd, Pr)-Hx addition. The present work suggests that tuning the distribution of Y is of crucial importance to further improve the coercivity of Y-containing permanent magnets.

Inferior intrinsic magnetic properties of (La/Ce)2Fe14B to Nd2Fe14B compound pose a big challenge for the Nd-La-Ce-Fe-B sintered magnets to provide an equivalent performance to the commercial Nd-Fe-B ones. To suppress the magnetic dilution, La/Ce distributions within 2:14:1 phase are intentionally tailored in the present work. At the same La-Ce substitution level of 12 wt%, the coercivity has been substantially increased to 1.36 T by constructing the coexisting Nd-rich shell @ La/Ce-rich core and La/Ce-rich shell @ Nd-rich core morphologies, compared to the La/Ce homogenously distributed magnet (0.76 T) and the one with singular Nd-rich core surrounded by La/Ce-rich shell (0.82 T). This is attributed to combined effects of magnetically hardening Nd-rich shell in suppressing the reversal domain nucleation, and continuous grain boundary layer in reducing the short-range exchange coupling between adjacent ferromagnetic grains. It may act as part of endeavors to promote the Nd-La-Ce-Fe-B sintered magnets for commercial application.

To balance the utilization of rare earth (RE) resource, abundant La has been incorporated into the Nd-Fe-B sintered magnets via the binary main phase (BMP) approach. Microstructure and magnetic properties of the Nd-La-Fe-B BMP magnets with increasing La substitution from 0 to 45 wt% were investigated. The results show that RE-rich intergranular phase with high oxygen content forms easily in the triple junction region for the La-substituted magnets. Those hcp-RE2O3 precipitates exhibit poor wettability with the matrix phase, leading to the direct exchange coupling of adjacent grains. As a result, the coercivity of Nd-La-Fe-B BMP magnets is dramatically reduced. Fortunately, the remanence can be maintained at a high level, ascribing to the inhomogeneous RE distributions among the grains (core-shell morphology), and the stable tetragonal phase after high-temperature sintering. With 27 wt% La substitution for Nd in the BMP magnet, the remanence decreases from 13.15 to 13.01 kGs by merely 1.06%. This work suggests that if one can optimize the microstructure by constructing magnetically isolated grains, low-cost Nd-La-Fe-B BMP magnets can be promising candidates for mass production.

SiO2 nanoparticles have been introduced into epoxy-modified silicone resin (ESR) via two routes including direct addition (DA) and in-situ growth (ISG). Growth mechanism of the SiO2 nanoparticles has been revealed where chemical bonding forms between the SiO2 and the epoxy, ester and hydroxyl groups of the ESR during ISG. The obtained hybrid resins have been used as the matrix in the fabrication of Fe soft magnetic composites (SMCs). Effects of the SiO2 incorporation method and its content on the magnetic, electrical and mechanical properties of the SMCs have been investigated. Optimized performance of the SMC with large effective permeability (107.9), reduced core loss (1220 mW/cm3) and enhanced mechanical strength (2.95 MPa) can be achieved by introduction of 34 wt% SiO2 nanoparticles into the ESR via ISG. The formation of chemical bonding between the SiO2 nanoparticles and the ESR also gives rise to improved thermal stability for complete stress relaxation of the SMCs.

Poor corrosion resistance is one major concern of RE2Fe14B-type (RE, rare earth) sintered magnets due to the large electrode potential difference between the ferromagnetic matrix phase and the RE-rich intergranular phase. The phase constituent within the intergranular region of high cost-performance Nd-La-Ce-Fe-B magnets, however varies with the La/Ce substitution level, and extra REFe2 phase forms over a critical La/Ce content. In this work, we performed a comparative study of two magnets prepared by single-main-phase (SMP, sintering the Nd-La-Ce-Fe-B powders free of REFe2 phase) or by binary-main-phase (BMP, sintering the mixture of Nd-Fe-B and Nd-La-Ce-Fe-B powders containing REFe2 phase) approaches to reveal the role of REFe2 phase on the corrosion resistance. The results show that the BMP magnet with additional REFe2 intergranular phase exhibits much better corrosion resistance against both hot/humid and saline environments than the SMP one having merely conventional RE-rich intergranular phase. It is attributed to that the REFe2 phase with higher electrode potential than RE-rich phase stabilizes the intergranular regions and lowers the driving force for electrochemical corrosion. Besides, REFe2 phase that locates mainly at the triple junctions suppresses the corrosion propagation and blocks the subsequent dissolution of RE2Fe14B grains. The Nd-La-Ce-Fe-B BMP magnets with improved corrosion resistance as well as the formerly reported superior magnetic performance to SMP ones are appealing for practical applications.

With CoCl2, NaBH4 and CNTs as the starting materials, the CoB/CNTs nanocomposites were successfully prepared and used as catalysts to improve the hydrogen storage properties of MgH2. CoB/CNTs catalysts were characterized by BET, SEM, and XRD. The results show that CoB/CNTs possesses high specific surface area. MgH2 doped with 10 wt% CoB/CNTs (MgH2+10 wt%CoB/CNTs) starts to release hydrogen at about 214 °C, and reaches a dehydrogenation peak at about 271 °C. These temperatures are 166 °C and 135 °C lower than that of commercial MgH2. The dehydriding/rehydriding kinetics of MgH2 are also remarkably improved by addition of CoB/CNTs. MgH2+10 wt%CoB/CNTs exhibits excellent isothermal hydrogen desorption kinetics at 300 °C. It can release around 5.5 wt% H2 within approximately 19 min, and can fully dehydride within 1 h. The maximum dehydridng rate reaches 22.9 wt%H2/h, which is 572 times faster than that of commercial MgH2. The activation energy of hydrogen desorption measured by Kissinger plot is estimated to be 89.1 kJ/mol for MgH2+10 wt% CoB/CNTs, which is reduced by 119.4 kJ/mol as compared to commercial MgH2. Moreover, The fully dehydrided MgH2+10 wt%CoB/CNTs product also shows excellent rehydriding properties, it can absorb up to 90% of hydrogen capacity within 20 s at 300 °C and 5 MPa H2. The catalytic mechanism is discussed.

The exploration of bio-derived materials for various applications has attracted considerable attention due to the global challenges of elemental sustainability. Herein, we report the synthesis of hollow-structure carbon fibers by carbonizing natural cotton at different temperatures. The microwave absorption properties are investigated, and the dielectric loss mechanism is studied furtherly. During the pyrolysis process, multi-elements such as oxygen, sulfur, and nitrogen existing in natural cotton can remain and in-situ doped into the carbonized fibers. And a high-concentration atomic-scale substitute is realized, which becomes the dielectric polarization site for microwave attenuation due to the symmetry breaking of localized charge. Moreover, the pyrolysis process results in forming a hollow structure of carbonized fibers, implying an ultra-low density of the resultant fibers. In the present study, it is found that the sample carbonized at 700 °C for 120 min (denoted as S700-120) exhibits the minimum reflection loss (RLmin) of − 51.9 dB at 12.1 GHz with the absorption bandwidth (fb) of 5.5 GHz when the thickness is 1.96 mm. The RLmin and fb for S700-80, S800-40, S800-80, and S800-120 are − 47.0 dB and 3.9 GHz, − 57.3 dB and 3.1 GHz, − 42.7 dB and 2.1 GHz, − 44.2 dB and 1.8 GHz, respectively, demonstrating a significant tunability of microwave absorption performances. Our work provides an alternative for the development of high-performance microwave absorbents from bio-sources.

In the design of advanced electromagnetic wave absorbing materials, composition and microstructure are critical to affect interactions between the incident waves with the absorbers. Here hierarchical SiO2@MoSe2@FeNi3 has been developed and impacts of evolution from core-shell, yolk-shell to hollow structures on the absorption performance has been investigated. Combination of the magnetic FeNi3 and the dielectric MoSe2 and SiO2 gives rise to synergistic and effective dissipation of the incident waves, whereas the impedance can be tuned by the size of the void during the microstructural evolution. Among the designed hierarchical SiO2@MoSe2@FeNi3, the yolk-shell composite exhibits enhanced absorption with a minimum reflection loss of − 45.25 dB over a wide effective absorption bandwidth of 6.80 GHz at a thickness of 1.4 mm due to optimal attenuation and impedance matching.

Resorcinol formaldehyde carbon aerogel (RFC)was synthesized in this paper to be used as a scaffold for nanoconfining 2LiBH 4 -LiAlH 4 composite. LiBH 4 and LiAlH 4 were nanoconfined into the pores of the prepared resorcinol formaldehyde carbon aerogel by a two-step melt-infiltration process. The microstructure evolution was investigated by XRD, FTIR analysis, and BET measurements. The hydrogen storage properties were studied by TPD, TG/DSC/MS measurements. The experimental results show that LiBH 4 and LiAlH 4 are well dispersed in the scaffold after the melt infiltration process. The nano-confined 2LiBH 4 -LiAlH 4 composite (denoted as 2LiBH 4 -LiAlH 4 /RFC) shows a two-step dehydrogenation process. The onset dehydrogenation temperatures for the two steps are 100 °C and 280 °C, respectively, which are 70 °C and 170 °C lower than that of the milled 2LiBH 4 -LiAlH 4 mixture. The formation of AlB 2 during the second dehydrogenation step alters the reaction pathway of LiBH 4 . The kinetic properties of the composite are greatly enhanced compared to the physical mixture of LiBH 4 and LiAlH 4 . The nanoconfinement and the formation of AlB 2 have a combined effect on the improvement of hydrogen storage properties for nanoconfined 2LiBH 4 -LiAlH 4 /RFC. It could be rehydrogenated at 350 °C and 5 MPa H 2 . A reversible hydrogen storage capacity of 5.7 wt.% is achieved.

Motivated by the global rare earth (RE) criticality, the utilization of abundant Ce and Y has attracted tremendous interests in the Nd-Fe-B community. Although the Y substitution can enhance the thermal stability of Nd-Ce-Fe-B magnet, the room-temperature coercivity is lowered drastically, which remains a challenging hurdle. Considering the equivalent intrinsic HA between Ce2Fe14B and Y2Fe14B compound, there is an intriguing possibility of achieving the balanced contributions from Y substitution on the improved coercivity and thermal stability of Nd-Ce-Y-Fe-B magnets simultaneously. Inspired by this possibility, a series of [Nd0.5(Ce1-xYx)0.5]30.5Fe68.5B1.0 melt-spun ribbons (x = 0–0.5, wt%) are prepared through adjusting the Ce/Y ratio in present work. Results show that maximized room-temperature coercivity Hcj of 12.0 ~12.2 kOe, together with preferable temperature coefficient α of −0.17 ~ −0.16%/K and β of −0.37 ~ −0.35%/K within 293–393 K interval are acquired at the optimal Y content (x = 0.1 and 0.2). Above outstanding combination of coercivity and thermal stability are the highest values reported so far upon 50 wt% Ce-Y substitution for Nd, which is ascribed to the intrinsic contribution from Y replacement for Ce in 2:14:1 lattice, as well as the microstructural advantages from refined RE2Fe14B grain and continuous RE-rich grain boundary layer. However, excessive Y substitution leads to dramatic grain growth and weakened exchanging coupling effect, drastically deteriorating the coercivity and remanence, despite the fact that both α and β are continually improved. Above findings shed new light on developing resource-saving Nd-Ce-Y-Fe-B permanent magnets with high synergy of coercivity and thermal stability.

Exploiting high-performance 2:14:1-type permanent magnet at high La–Ce substitution level remains a bottleneck concern due to the severe magnetic dilution from inferior intrinsic magnetism and microstructural deterioration. In present work, to promote the La–Ce application, (Pr, Nd)Hx is introduced into LaCe-40 sintered magnet (La–Ce/TRE = 40 wt%, TRE: total rare earth) through two approaches, grain boundary restructuring (GBR) and grain boundary diffusion process (GBDP). Results show that (Pr, Nd)Hx GBR leads to a twofold coercivity by optimizing the distribution of GB phase and forming a Pr/Nd-rich magnetically hardening shell. However, the remanence is lowered drastically due to massive formation of REFe2 phase during high-temperature sintering. Comparably, (Pr, Nd)Hx GBDP magnet with an identical average composition to GBR one yields a nearly threefold coercivity without sacrificing the remanence, ascribing to the formation of more continuous RE-rich GB layer and thicker Pr/Nd-rich shell near the surface region. Above comparative study highlights the crucial role of surface magnetic isolation in enhancing the coercivity of Nd–La–Ce–Fe–B sintered magnet, and delights the prospect of abundant La–Ce for industrial application.

Soft magnetic composites (SMCs) containing Fe powders embedded in insulating matrix have been fabricated via alkaline bluing as a new method. Effects of reaction time on the magnetic properties of the SMCs have been investigated. Mechanism of the oxidation process has also been revealed, which involves initial oxidation of Fe into Fe 2+ (Na 2 FeO 2 ) and Fe 3+ (Na 2 Fe 2 O 4 ) by NaNO 2 and NaNO 3 followed by hydrolysis of Fe 2+ and Fe 3+ into Fe 3 O 4 . Hydrolysis of the excessive Fe 3+ leads to the formation of Fe 2 O 3 which reduced the effective permeability of the SMCs. To form pure Fe 3 O 4 coating, the reaction process has been improved to suppress the Fe 3+ hydrolysis. The obtained ferromagnetic Fe 3 O 4 coating effectively reduces magnetic dilution, while its high electrical resistivity allows satisfactory insulation between the Fe powders, giving rise to simultaneous high effective permeability (97.7) and low core loss (771.3 mW/cm 3 ) of the SMC.

A simple and facile method has been provided to develop novel core-heteroshell electromagnetic (EM) wave absorbers via selenylation of FeNi3 nanoparticles. Core-heteroshell composites containing multiple phases including the FeNi3, NiFe2O4 and NiSex can been obtained with increased surface gradient of Se with the growth mechanisms revealed. Not only synergistic effects of magnetic and dielectric attenuation have been introduced, the multiple components also give rise to tunable impedance and enhanced interfacial polarization for improved EM wave absorbing performance. Such effective one-step route may be extendable to achieve core-heteroshell structure with multiple components for applications in other fields including energy, catalysis and sensing.

While most studies on high-entropy alloys (HEAs) are focused on their potential applications as structural materials, the consideration in research as potential functional materials is still preliminary. This paper presents a comprehensive analysis of the microstructure, phase constitution and magnetic properties of the FeCoNi(AlMn)x (0.1 ≤ x ≤ 1.0) with the aim of developing the potential technological applications of HEAs soft magnetic materials. The results show that the addition of AlMn into FeCoNi alloy leads to the phase transition from FCC to BCC for the HEAs, which results in the increase of hardness and electrical resistivity (ρ). Owing to the synergistic effect of Al and Mn elements, the alloy with lower energy losses can be obtained when x = 0.5, whereas the alloy shows higher μi, μm, Bm, Ms, AC Bm when x = 1.0. Furthermore, compared with other soft magnetic materials, the FeCoNi(AlMn)x HEAs exhibit a superior combination of magnetic, electrical and mechanical properties. Therefore, this work showcases possible applications of each HEAs as soft magnetic materials in functional magnetic elements.

Fe soft magnetic composites (SMCs) containing Fe powders embedded in Fe3O4/epoxy-modified silicone resin (ESR) matrix have been fabricated via thermal oxidation of Fe powders with H2O under alkalic conditions, prior to mixing with ESR. The ferromagnetic Fe3O4 coating effectively reduces magnetic dilution, while high electrical resistivity of both Fe3O4 and ESR provides satisfactory insulation of the SMCs, giving rise to simultaneous high permeability and low core loss. Evolution of the Fe3O4/ESR matrix during the annealing process has been investigated, which is correlated to changes in the magnetic properties of the SMCs. The ESR starts to decompose at around 382 °C, leaving reducing groups which then convert the Fe3O4 coating into Fe with increased annealing temperature to 466 °C. Further raised annealing temperature to 570 °C leads to the reduction of Fe3O4 into FeO. Such evolution provides in-sight information on choosing appropriate annealing conditions to avoid decomposition of the Fe3O4/ESR matrix and can be expanded to other Fe-based SMCs.

Fe73.5Cu1Nb3Si15.5B7 amorphous alloy was fabricated into nanocrystalline soft magnetic composites (SMCs). Crystallization process and the evolution of stress relaxation of the SMCs during annealing have been investigated and their effects on the magnetic properties are revealed. Crystallization of the amorphous alloy is accomplished by increment of nucleation sites with the annealing temperature ranged from 500 °C to 600 °C. Stress induced by milling and compaction relieves with increased annealing temperature and complete relaxation can be achieved at around 575 °C. Coupling of small grains (9.1 nm–12.8 nm) and stress relaxation ensures the FeCuNbSiB SMCs of relatively low coercivity, high permeability and low loss. Further raised annealing temperature above 600 °C leads to dominating growth and coalescence of the existing α-Fe(Si) grains and the precipitation of the Fe23B6 phase, which deteriorates the magnetic properties. Optimized soft magnetic properties of the SMCs such as small coercivity (4.5 Oe), large effective permeability (115) and low total core loss (200 mW/cm3 measured when Bm = 0.1 T and f = 50 kHz) can be achieved by post-annealing at 575 °C.

The tungsten–copper alloys were prepared and characterized utilizing pressureless microwave sintering and hot pressure microwave sintering. The performance of tungsten–copper alloy was assessed based on the relative density and hardness. The influence of different pressure and copper content on the microstructure of tungsten copper alloy has been investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Experimental results indicate tungsten–copper alloy with excellent performance under microwave hot press sintering. The relative density of the alloy was estimated to be 98.14% at a sintering temperature of 1100 °C, applied pressure of 30 MPa for duration of 1 h. The relative density was found to increase with increase in the applied pressure. The microstructure of tungsten–copper alloy sintered by microwave hot press method was more uniform having a compact matrix.

A series of Co 3 O 4 /Ketjen Black cathodes are fabricated by electrostatic spray deposition technique for Li–O 2 batteries. A sluggish kinetics of oxygen reduction reaction and oxygen evolution reaction processes is noted either when Co 3 O 4 is lacked or Ketjen Black is insufficient, which leads to much higher overpotentials between charge and discharge profiles. By contrast, with the optimal design in terms of electric conduction and catalytic activity, the Co 3 O 4 /Ketjen Black (80 wt%) composite achieves enhanced electrochemical performance with an initial discharge capacity of 2044 mAh g −1 and maintaining 33 cycles at a fixed capacity of 500 mAh g −1 . The electrochemical characterization indicates that the improved Li–O 2 battery performance may benefit from the highest oxygen reduction reaction and oxygen evolution reaction activity under this electro-chemically optimized composite. This work may shed light on the design principle of future cathode materials for Li–O 2 batteries.

The FeNi3, MoSe2 and MoSe2@FeNi3 hollow nano-spheres synthesized by wet chemical method are used for the first time to improve the hydrogen storage properties of the MgH2. The results show that they all possess excellent catalytic activity in the hydrogen desorption/sorption reactions of MgH2. Because of the synergistic catalytic effect of MoSe2 and FeNi3, the MoSe2@FeNi3 has the most outstanding catalytic effect. In detail, the onset dehydrogenation temperature of MgH2 is reduced from 310 °C to 194 °C, and its maximum dehydrogenation rate is increased by 19.8 times by the introduction of 10 wt% MoSe2@FeNi3. Furthermore, the 10 wt% MoSe2@FeNi3-doped MgH2 sample, 5.8 wt% H2 can be absorbed in 0.5 min at 150 °C. However, the un-doped MgH2 sample hardly absorbs hydrogen under the same conditions. The onset hydrogen absorption temperature of the composite is only 73 °C. More importantly, it has an excellent cycling stability. These improvements are because the in situ formed MgSe, Mo, Mg2Ni and Fe can serve as active species, and they as well as their homogeneous distribution on MgH2 matrix can remain stable during dehydrogenation/hydrogenation. In addition, the presence of Mg2Ni can convert MgH2 to an easier pathway of hydrogen absorption/desorption. These help to facilitate the hydrogen storage performance of MgH2.

Nowadays, the magnetic materials with special functional characteristics are played very important roles in the development of our present modern society. The magnetic refrigeration (MR) technology which is based on the magnetocaloric effect (MCE) of magnetic solids has been considered as an energy-efficient alternative method to our present well used gas compression/expression refrigeration technology. The commercial products of magnetic refrigerators are still in the developing stage, searching and designing magnetic solids with outstanding MCE performances is one of the most important tasks at present. This paper briefly reviewed our recent progress in the investigation of the crystal structure, magnetic properties and magnetocaloric performances in several series of binary and ternary rare earth (RE) based intermetallic compounds. Some of them have been found to exhibit promising magnetocaloric performances at low temperatures which make them be considerable for cryogenic MR application.

Phosphate layers were prepared as the insulation coating for Fe and FeSiAl soft magnetic composites (SMCs) and mechanisms of the phosphating process have been investigated. Effects of high-temperature annealing on the phosphate coating and the magnetic properties of the SMCs have also been revealed. For Fe SMCs, the insulating coating mainly consists of iron phosphate after surface passivation. It degrades into iron phosphide after annealing at relatively high temperatures (600 °C), leading to decreased electrical resistivity and increased eddy current for deteriorated magnetic properties of Fe SMCs. For the FeSiAl SMCs, the phosphate coating mainly contains Al(PO 3 ) 3 , which converts into oxides such as Al 2 O 3 and P 2 O 5 after annealing. These oxides possess high electrical resistivity, and continue to serve as the insulation coating for the composites. Consequently, the resistivity of the FeSiAl SMCs increases with the annealing temperature, which is beneficial to decrease the eddy current loss for enhanced magnetic performance.

ErCo 2 compound is a well-known magnetocaloric material which shows giant magnetocaloric effect in the vicinity of first-order phase transition. We demonstrate a new way of fine tuning its crystal structure and magnetic properties. Er atomic vacancies are introduced in order to manipulate the local atomic environment, the phase transition characteristics, and the magnetocaloric effect as well. Er 1− x Co 2 can be stable over a narrow homogenous range, and maintain the cubic structure. The Bragg peaks shift upward to higher angles, and the unit cell volume contracts with reduction of the Er content. The Curie temperatures in low magnetic field increase from 32 K (ErCo 2 ) to 46 K (Er 0.97 Co 2 ), and linearly change with the magnetic field in nearly same slope. Er 1− x Co 2 compounds exhibit anomalous susceptibility behaviors in the paramagnetic state, and deviate from the Curie–Weiss law at around 100 K. The temperature range of anomalous susceptibility behaviors also move upward to higher temperature with reduction of Er content. Er 1− x Co 2 compounds also show anomalous coercivity behavior in the vicinity of phase transition. Er 1− x Co 2 compounds exhibit large magnetocaloric effect and good refrigerant capacity in the vicinity of ferrimagnetic–paramagnetic phase transition.

In order to improve the coercivity of Nd–Fe–B sintered magnets, DyH2 and DyH3 fine powders were prepared and used as additive for preparing Nd–Fe–B sintered magnets. The effects of DyHx powders addition on the microstructures and the magnetic properties of the magnets have been investigated. It was found that hydrogen will react with oxygen of NdOx rich intergranular phases to form Nd rich phases by dysprosium hydride addition. The Nd-rich grain boundary phases are more homogenous and continuous because the volume fraction of Nd-rich grain boundary phases increases with respect to the Nd oxide phases. After desorption, fine dysprosium powders become more active and wrap matrix phases well so that the diffusion of dysprosium to the surface layer of matrix phases is convenient, so dysprosium decreases in grain boundary phases and aggregates in surface layer of matrix phases. Then, intrinsic coercivity of NdFeB sintered magnets is improved from 14.96 kOe to 20.5 kOe and 20.31 kOe by 2.0 wt.% DyH3 and 2.0 wt.% DyH2 addition, respectively. This study has shown that DyHx addition can reduce the content of oxygen in grain boundary phases. This can be an effective method for massive production.

Although lower rare-earth content (REC) Nd–Fe–B sintered magnets possess better corrosion resistance, it is hardly to achieve full densification and high magnetic performance for near-stoichiometric Nd 2 Fe 14 B magnets. To improve magnetic performance and corrosion resistance simultaneously, Nd 64 Co 36 eutectic alloy powders are added into (Pr, Nd) 29.00 Fe 69.75 Ga 0.20 B 1.05 (wt.%) sintered magnets. With 0.5 wt.% addition, continuous thin grain boundary layers are formed for their better wettability with the (Pr, Nd) 2 Fe 14 B matrix phase. The coercivity H cj is hence enhanced from 9.94 to 13.01 kOe without deteriorating remanence B r , resulting in an obvious increase of maximum magnetic energy product ( BH ) max from 40.02 to 47.93 MGOe accordingly. In comparison with the 48 MGOe commercial magnets, such performance is superior, but the REC is 1.24 wt.% lower, which leads to an improved corrosion resistance and reduced cost. Further investigations reveal that the stability enhancement of the intergranular phase results from the formation of more stable Co-containing phases and oxides within the intergranular regions and the blocked corrosion channels by them.

The CuW80 alloy was prepared by the method of microwave vacuum sintering. The effects of temperatures on the performance of CuW80 alloy was assessed based on the relative density and hardness. The micro structure of alloy was characterized using scanning electron microscopy, while XRD was utilized to identify the structure changes. Experimental results indicate CuW80 alloy with excellent performance under vacuum conditions prepared by microwave sintering. Density was found to increase with increase in sintering temperature linearly until 1200 C, while the rate of increase was found to reduce at higher temperatures, reaching an asymptote. The maximum relative density of the alloy was estimated to be 97.95% at 1300 C. At a sintering temperature of 1200 C, CuW80 alloy was more uniform with the main phase of alloy being Cu0.4W0.6 (PDF: 50-1451) and maximum hardness being 222 HBS.

Effects of compaction and annealing process on the magnetic properties and microstructures of molybdenum permalloy (MP) powder cores have been investigated. MP compacts, with density as high as 92% of the theoretical value, were obtained under 1800 MPa compaction pressure. The MP powder cores show an enhanced effective magnetic permeability of 160 after post-annealing at 690 °C, which is attributed to the relief of internal stress rather than the phase transformation evidenced by the XRD analysis. However, higher annealing temperature destroys the insulating layer, resulting in the drop of the electrical resistivity, the effective magnetic permeability as well as the frequency stability. The results show that the samples compacted at 1800 MPa and annealed at 690 °C exhibit excellent magnetic properties, with core loss of 780 mw/cm 3 (100 kHz, 100 mT) and effective magnetic permeability of 160 whose frequency stability is up to 1 MHz.

Nd–Dy–Fe–B magnets require a prolonged high temperature sintering process because of the enlarged melting point of intergranular (Dy,Nd)-rich phase, which subsequently results in abnormal grain growth of the Nd2Fe14B matrix phase. In this work, in order to achieve higher coercivity and maintain the remanence Br simultaneously, Ta was introduced into Nd–Dy–Fe–B magnets through intergranular addition. With the addition of 0.2 wt.%, the average grain size of the matrix phase was reduced from 22.4 μm to 8.7 μm, and the coercivity Hcj can be enhanced from 16.7 kOe to 17.7 kOe without sacrificing Br. It is found that Ta entered mainly into the intergranular regions and rarely located inside the matrix phase, hence hindering the abnormal growth of Nd2Fe14B grains. In addition, stability of the intergranular phase was also improved, which leads to better corrosion resistance of the magnets against both electrochemical and hot/humid environments.

A facile and scalable process for synthesizing Fe3O4/C composites via a solution combustion technique followed by carbon-coating annealing treatment is developed. The as-prepared Fe3O4/C sample containing about 13.9 wt% carbon displays an attractive cycling performance up to 100 cycles (∼470 mA h g−1 retained at 100 mA g−1). In addition, the Fe3O4/C electrode shows good rate capability, a capacity of 530 mA h g−1 at 92.4 mA g−1 is still recoverable and sustainable up to 60 cycles after charge/discharge process at high rates. The enhanced electrochemical performance can be attributed to the improved electron transport from the consecutive carbon layer and Li+ diffusion due to the nanoscale nature of the Fe3O4 active materials. The present work represents a successful example of solution combustion technique combined with carbon-coating annealing process for preparing iron oxide-based electrodes in large scale, which can also be extended to prepare other metal oxide/carbon composites.

Lithium alloys and metal oxides have been widely recognized as the next-generation anode materials for lithium-ion batteries with high energy density and high power density. A variety of lithium alloys and metal oxides have been explored as alternatives to the commercial carbonaceous anodes. The electrochemical characteristics of silicon, tin, tin oxide, iron oxides, cobalt oxides, copper oxides, and so on are systematically summarized. In this review, it is not the scope to retrace the overall studies, but rather to highlight the electrochemical performances, the lithium storage mechanism and the strategies in improving the electrochemical properties of lithium alloys and metal oxides. The challenges and new directions in developing lithium alloys and metal oxides as commercial anodes for the next-generation lithium-ion batteries are also discussed.

Sintered Nd–Fe–B magnets with various degrees of grain alignment are prepared by the conventional powder metallurgy technique. The magnetic properties, bending strength and fracture morphologies of sintered magnets with different alignment degrees are investigated. The results show that the remanence B r and maximum energy product ( BH ) max increase, while intrinsic coercivity H cj decreases gradually with increasing the alignment degree. Moreover, the bending strengths measured by applying force parallel ( σ bb∥ ) and perpendicular ( σ bb⊥ ) to the alignment magnetic field H appl present opposite variation tendency, and σ bb∥ is larger than σ bb⊥ , suggesting the more significant anisotropy of mechanical properties with increasing the degree of grain alignment. Furthermore, the related mechanisms are systematically analyzed.

The effect of defects in the diluted magnetic semiconductor (DMS) of Fe and Na co-doped ZnO nanoparticles was investigated. Structural characterizations revealed that Fe and Na ions enter into ZnO lattice without any secondary phase. The ferromagnetic behaviors at room temperature were found in all samples, which are attributed to the exchange via electron trapped oxygen vacancies (F-center) coupled with magnetic Fe ions. With the increase of the Na concentration, the oxygen vacancy mediated ferromagnetic state is enhanced. The observed correlation between the Na concentration, the carrier concentration and the magnetization revealed the role of the defect in tuning the ferromagnetism in the ZnO-based DMS system.

To improve the dehydrogenation properties of LiBH4, a novel hydrogen storage system, LiBH4–Li3AlH6, was synthesized by mechanical ball milling. The dehydrogenation/rehydrogenation properties of LiBH4–Li3AlH6 (molar rato: 1:1) composites were studied via thermogravimetry (TG), differential scanning calorimetry (DSC), mass spectral analysis (MS), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The experimental results show that the hydrogen desorption capacity reaches 8.5 wt% and that the whole dehydrogenation is a three-step process: (1) a decomposition reaction Li3AlH6 → 3LiH + Al + 3/2H2, occurring at 160 °C; (2) formation of an intermediate product from 300 °C to 350 °C, and then subsequent transformation into Al, AlB2, and H2. (2LiBH4 + Al → [Li2B2AlH4] → x(AlB2 + 2LiH + 3H2) + (1 − x) [Li2B2AlH4], (0 < x < 1)); and (3) final dehydrogenation of LiH + Al → LiAl + 1/2H2, occurring at 415 °C, with sequential decomposition of the remaining intermediate ((1 − x)[Li2B2AlH4]→(1 − x)(AlB2 + 2LiH + 3H2), (0 < x < 1)). Furthermore, the dehydrogenated products can be rehydrogenated to LiBH4 at 8 MPa H2 and 400 °C.

The Nd7Y2.5Fe64.5Nb3B23 nanocomposite permanent magnets in the form of rods with 2 mm in diameter have been developed by annealing the amorphous precursors produced by copper mold casting technique. The phase evolution, structure, magnetic and mechanical properties were investigated with X-ray diffractometry, differential scanning calorimetry, electron microscopy, magnetometry and universal uniaxial compression strength techniques. The heat treatment conditions under which the magnets attained maximum magnetic and mechanical properties have been established. The results indicate that magnet properties are sensitive to grain size and volume content of the magnetic phases present in the microstructure. The composite microstructure was mainly composed of soft α-Fe (20–30 nm) and hard Nd2Fe14B (45–65 nm) magnetic phase grains. The maximum coercivity of 959.18 kA/m was achieved with the magnets annealed at 760 °C whereas the highest remanence of 0.57 T was obtained with the magnets treated at 710 °C. The optimally annealed magnets possessed promising magnetic properties such as jHc of 891.52 kA/m, Br of 0.57 T, Mr/Ms = 0.68, (BH)max of 56.8 kJ/m3 as well as the micro-Vickers hardness (Hv) of 1138 ± 20 and compressive stress (σf) of 239 ± 10 MPa.

High-quality uniform SnO2 thin films were successfully prepared by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) method, using a cost-efficient precursor of (Bu2Sn)-Bu-n(acac)(2). The volatility and stability of (Bu2Sn)-Bu-n(acac)(2) were studied through thermogravimetric-differential thermal (TG-DTA) analysis and mass spectrometry, indicating the good adaptability for the CVD process. Deposition of SnO2 films was made in the range of 250-450 degrees C to investigate the effect of substrate temperature on their structural and physical properties. The film growth activation energy changes from 66.5 kJ/mol in the range of 250-330 degrees C to 0 kJ/mol at 330-450 degrees C, suggesting the change of the rate-limiting step from surface kinetics to diffusion control. All films possess the rutile-type tetragonal structure, while a change of preferred orientation from (1 1 0) to (1 0 1) plane is observed upon the increase of the deposition temperature. The different variation of the nucleation and growth rates with the deposition temperature is proposed to explain the observed unusual change of crystallite size. A significant deterioration of the electrical conductivity was observed upon the increase of the deposition temperature, which was tentatively attributed to the non-specific decomposition of the precursor at high temperature leading to carbon contamination. Optical measurements show transparencies above 80% in the visible spectral range for all films, while band gap energy increases from 4.02 eV to 4.08 eV when the deposition temperature was raised from 250 degrees C to 450 degrees C. (C) 2011 Elsevier B.V. All rights reserved.

Low-temperature reactive pulsed laser deposition (PLD) was used to prepare iron nitride films. The textured γ′-Fe 4 N films with (0 0 1)-orientation were deposited on Si (1 0 0) substrate with Fe buffer layer at a substrate temperature as low as 150 °C. The (0 0 1)-oriented γ′-Fe 4 N film grew on the Fe buffer layer with a 3.5-nm thick amorphous interlayer, which eliminated the lattice mismatch stress between them. The films showed a columnar granular morphology with an average lateral grain size of approximately 110 nm. The films exhibited good soft magnetic properties with a high in-plane M r / M s value of 0.84. The magneto-optic Kerr effect results indicated an in-plane magnetic isotropy and confirmed the high remnant ratio of the γ′-Fe 4 N films.

A series of [(Fe 1− x Co x ) 72 Mo 4 B 24 ] 94 Dy 6 ( x = 0.1, 0.2, 0.3, 0.4 and 0.5 at.%) bulk metallic glasses (BMGs) in rod geometries with critical diameter up to 3 mm were fabricated by copper mold casting method. This alloy system exhibited good thermal stability with high glass transition temperature ( T g ) 860 K and crystallization temperature ( T x ) 945 K. The addition of Co was found to be effective in adjusting the alloy composition deeper to eutectic, leading to lower liquidus temperature ( T l ). The [(Fe 0.8 Co 0.2 ) 72 Mo 4 B 24 ] 94 Dy 6 alloy showed the largest supercooled liquid region (Δ T x = T x − T g = 92 K), reduced glass transition temperature ( T rg = T g / T l = 0.622) and gamma parameter ( γ = T x /( T g + T l ) = 0.424) among the present system. Maximum compressive fracture strength of 3540 MPa and micro-Vickers hardness of 1185 kg/mm 2 was achieved, resulting from the strong bonding structure among the alloy constituents. The alloy system possessed soft magnetic properties with high saturation magnetization of 56.61–61.78 A m 2 /kg and coercivity in the range of 222–264.2 A/m, which might be suitable for application in power electronics devices.

(Fe 72 Mo 4 B 24 ) 100− x Tb x ( x = 4, 5, 6, 7 at.%) bulk glassy alloys with diameter of 2 mm were prepared by copper mold casting. The influence of Tb content on glass forming ability was investigated. There is partial crystallization in the alloy when x = 4, while fully amorphous alloys with no detectable crystallization are obtained for x = 5, 6, 7, respectively. DSC curves of the amorphous alloys indicate that this system exhibits a high glass transition temperature ( T g = 848–927 K) and a wide supercooled liquid region up to 104 K. The best glass forming ability is obtained for x = 5. These bulk metallic glasses exhibit good mechanical properties, with the compressive strength up to 3163 MPa, and H v up to 1149. In addition, the alloys exhibit relatively good soft magnetic properties, with M s up to 69.205 emu/g and H c as low as 4 Oe.

To improve the corrosion resistance and magnetic properties, Al85Cu15 (at.%) compound powders were added to (Pr, Nd)14.8Fe78.7B6.5 sintered magnets as grain boundary modifiers. The corrosion resistance was found to be remarkably improved by small additions of Al85Cu15 powders. When 1.2 wt% Al85Cu15 was added, the corrosion rate of magnets in humid environments was reduced by two orders of magnitude. This is partly due to the stability enhancement of the (Pr, Nd)-rich intergranular phase by Cu and Al. In addition, the occurrence of the Cu-rich phase ((Pr, Nd)22Fe56Cu10Al2O10), whose open-circuit potential is higher than the (Pr, Nd)-rich intergranular phase, may be another reason for the improvement of the corrosion resistance. Furthermore, the magnetic properties of (Pr, Nd)14.8Fe78.7B6.5 were also improved by adding 0.3–1.2 wt% Al85Cu15. Optimum addition amount was 0.6 wt%. The improvement of the magnetic properties may be related to the microstructural modification and the increase of magnet density.

The newly discovered large magnetostriction in antiferromagnetic γ-Mn–Fe alloy is of interest to develop a new kind of ductile and low-cost magnetostrictive materials. This work presents a detailed study on the structures, magnetostrictive, and magnetic properties of a heat-treated Mn42Fe58 alloy by X-ray diffraction (XRD), transmission electronic microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometer. The single γ-phase separates into a mixture containing a face-centered-cubic (fcc) γ-phase, a hexagonal close-packed (hcp) ɛ-phase, and a body-centered-cubic (bcc) α-phase after isothermal heat treatment for 24 h at 1100 °C. Such phase separation in Mn42Fe58 alloy not only leads to a slight increase in lattice parameter a of the γ-phase and Neel temperature TN, but also results in an obvious enhancement in magnetization due to the presence of ferromagnetic bcc phase. The magnetostrictive performance, however, deteriorates accompanying with the phase separation.

Ni–ZrO2 functionally graded materials (FGMs) have been fabricated via slip casting under a series of gradient magnetic fields. The effects of field gradient, holding time and Ni concentration on microstructures of Ni–ZrO2 FGMs were investigated. A Ni composition gradient was formed along the field direction in Ni–ZrO2 FGMs, and increased when the magnetic field gradient increased from 0.5 to 3.0 T/m. Moreover, the composition gradient also increased with the prolongation of holding time. However, the composition gradient decreased as Ni concentration increased from 4 to 15 wt.%, which can be attributed mainly to the formation of Ni clusters. A schematic model was proposed to explain the distribution of particles in gradient magnetic fields.

The magnetic and magnetotransport properties of polycrystalline Er1-xDyxMn6Sn6 (x = 0-0.6) compounds have been investigated in the temperature interval of 5-435 K. The compounds with low Dy concentration (x = 0-0.1) show ferrimagnetic and antiferromagnetic behavior, (T-N = 346-349 K). The Dy-rich compounds (x = 0.3-0.6) behave ferrimagnetically (T-C = 365-380 K). The intermediate compounds (x = 0.2-0.26) display ferrimagnetism, antiferromagnetism, re-entrant ferrimagnetism, and paramagnetism with increasing temperature. In the antiferromagnetic state (x = 0-0.26), the transition from antiferromagnetism to ferrimagnetism can be induced by an applied field, and the metamagnetic transition field decreases monotonously with increasing x, such as from 15.5 kOe for x = 0 to 1.5 kOe for x = 0.26 at 253 K. A large magnetoresistance(MR) effect is observed with the metamagnetic behavior, e.g. MR = -9.7% for x = 0 at 125 K in a field of 50 kOe. It is interestingly observed that the Er1-xDyxMn6Sn6 (X = 0 and 0.26) compounds display the positive. MR effect in the low-temperature ferrimagnetic state,which is likely due to the scattering of the conduction electrons by the nonmagnetic Sn layers. (C) 2003 Elsevier B.V. All rights reserved.