The low coercivity is the major factor inhibiting the large-scale commercial utilization of Nd-Ce-Fe-B sintered magnets.In this work,we achieved a record-high coercivity of 15.04 kOe in Ga-doped Nd-Ce-Fe-B sintered ma...The low coercivity is the major factor inhibiting the large-scale commercial utilization of Nd-Ce-Fe-B sintered magnets.In this work,we achieved a record-high coercivity of 15.04 kOe in Ga-doped Nd-Ce-Fe-B sintered magnets with 30 wt%Ce replacing Nd,demonstrating enormous potential.The Ga-doped Nd-Ce-Fe-B magnets with higher boron(HB)and lower boron(LB)content are designed.The coercivity of the HB magnet increases slightly from 10.80 to 12.26 kOe after annealing,attributed to the optimized distribution of grain boundary(GB)phases.In contrast,the coercivity of the LB magnet remarkably increases from 8.13 to 15.04 kOe after annealing.Microstructural observations indicate that the narrow GB phase in the as-sintered magnet is rich in Fe,and the strong exchange coupling of adjacent grains resulted in low coercivity.The evolution of Ga-rich phases reveals a potential formation mechanism of the RE_(6)Fe_(13)Ga phase,that is the RE-Fe amorphous phase and REGa phase in the as-sintered magnet combine to form the RE_(6)Fe_(13)Ga phase and RE-Ga amorphous phase during post-sinter annealing(RE:rare earth).Moreover,the GB phase of the annealed magnet transforms into a Fe-lean phase with a thickness of 16.4 nm.Magnetization and demagnetization behavior characterizations reveal that the exchange decoupling of adjacent grains induced by the optimized GB phases is the main reason for the remarkable coercivity enhancement,which is also validated by micromagnetic simulations.展开更多
Nanocrystalline Ce-based rare earth(RE)-Fe-B alloys exhibit relatively good hard magnetic properties and high performance-cost ratio,but their properties deteriorate seriously after hot deformation(HD).Here,we present...Nanocrystalline Ce-based rare earth(RE)-Fe-B alloys exhibit relatively good hard magnetic properties and high performance-cost ratio,but their properties deteriorate seriously after hot deformation(HD).Here,we present a simplified one-step HD process for preparing anisotropic Ce-based Ce_(25.88)La_(2.85)Y_(4.56)Fe_(65.73)B_(0.98)(wt%)magnets.The precursor of nanocrystalline powders is first compacted inside a copper tube,and then the powders with the tube are deformed together to achieve magnetic anisotropy.Compared with the conventional two-step HD magnet,i.e.,hot pressing followed by HD,one-step HD significantly increased the coercivity from 1.6 to 3.0 kOe,and the maximum magnetic energy product was improved from 3.7 to 4.8 MGOe.The microstructure characterization indicates that one-step HD can not only produce a more desirable microstructure,characterized by well-aligned platelet-shaped grains with reduced aspect ratio but also greatly inhibit the formation of coarse grain(CG)region.Both of them have been confirmed to be beneficial to enhancing coercivity by micromagnetic simulations.Our results thus demonstrate that the simplified one-step HD process offers a promising approach to developing high-performance anisotropic Ce-based magnets.展开更多
In this study,to enhance the coercivity and high-temperature stability of hot-deformed PrNd-Fe-B magnets,the NdHoAlGa alloy was utilized as a diffusion source and a dual-alloy diffusion process was employed to enhance...In this study,to enhance the coercivity and high-temperature stability of hot-deformed PrNd-Fe-B magnets,the NdHoAlGa alloy was utilized as a diffusion source and a dual-alloy diffusion process was employed to enhance the room temperature coercivity from 1.72 to 2.28 T.For the magnet doped with7 wt%Nd_(72.3)Ho_(13).8Al_(2.3)Ga_(11.7),within the temperature range from 20 to 200℃,the remanence temperature coefficient a increases from-0.16%/℃to-0.14%/℃,and the coercivity temperature coefficientβincreases from-0.49%/℃to-0.43%/℃.By controlling grain boundary(GB)phases and optimizing the main phase simultaneously,Ga was induced to motivate the formation of non-ferromagnetic GB phases,reducing the size of grains and intergranular exchange coupling.Additionally,Ho was diffused into the main phase,forming(Pr,Nd,Ho)-Fe-B phase,which enhances the magnetic crystalline anisotropy field of the main phase grains at high temperatures.展开更多
Spinel cubic ferrites have huge applications in me mory and high frequency devices.For the improvement of these modern devices,the magnetic coercivity,permeability,and dielectric properties of a ferrite are the import...Spinel cubic ferrites have huge applications in me mory and high frequency devices.For the improvement of these modern devices,the magnetic coercivity,permeability,and dielectric properties of a ferrite are the important issues.This article focuses on improving the magnetic coercivity,magnetic permeability,and dielectric properties of Co_(0.2)Zn_(0.3)Ni_(0.5)Eu_(x)Fe_(2-x)O_(4) ferrites,where x=0.00,0.06,and 0.10.The X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscopy(FESEM),energy dispersive X-ray(EDX),vibrating sample magnetometer(VSM),and an impedance analyzer were used to characterize the structural,magnetic,and dielectric properties of the samples.The XRD patterns indicate the formation of spinel cubic structure of the samples with a secondary peak(EuFeO_(3))for Eu doped samples.The densities and porosities of the samples follow an inverse trend,where the doped samples’lattice parameters are increased with the increment of rare earth Eu concentration.The FTIR analysis also proves the spinel cubic phase of the samples.The average grain size of the ferrites is obtained via FESEM images,and it is increased from 121 to 198 nm.VSM analysis confirms that doping of the Eu content also changes other hysteresis loop properties of Co_(0.2)Zn_(0.3)Ni_(0.5)Eu_(x)Fe_(2-x)O_(4) ferrites.Particularly,the coercivity of the Eu doped samples is greater than that of the mother alloy(x=0.00).The EDX study shows that there is no impurity contamination in the ferrites.The permeability and dielectric measurements show an improved quality factor of the Eu-doped samples with low magnetic and dielectric losses.Frequency dependent resistivity and impedance analysis also show the improved nature.From the observed properties of the samples,all the investigated ferrites might be strong candidates for potential applications in memory devices,magnetic sensors,and high frequency applications.展开更多
Overcoming the trade-offbetween saturation magnetic induction(B_(s))and coercivity(H_(c))of Fe-based nanocrystalline alloys(FNAs)remains a great challenge due to the traditional design relying on trial-anderror method...Overcoming the trade-offbetween saturation magnetic induction(B_(s))and coercivity(H_(c))of Fe-based nanocrystalline alloys(FNAs)remains a great challenge due to the traditional design relying on trial-anderror methods,which are time-consuming and inefficient.Herein,we present an interpretable machine learning(ML)algorithm for the effective design of advanced FNAs with improved B_(s)and low H_(c).Firstly,the FNAs datasets were established,consisting of 20 features including chemical composition,process parameters,and theoretically calculated parameters.Subsequently,a three-step feature selection was used to screen the key features that affect the B_(s)and H_(c)of FNAs.Among six different ML algorithms,extreme gradient boosting(XGBoost)performed the best in predicting B_(s)and H_(c).We further revealed the association of key features with B_(s)and H_(c)through linear regression and SHAP analysis.The valence electron concentration without Fe,Ni,and Co elements(VEC1)and valence electron concentration(VEC)ranked as the most important features for predicting B_(s)and H_(c),respectively.VEC1 had a positive impact on B_(s)when VEC1<0.78,while VEC had a negative effect on H_(c)when VEC<7.12.Optimized designed FNAs were successfully prepared,and the prediction errors for B_(s)and H_(c)are lower than 2.3%and 18%,respectively,when comparing the predicted and experimental results.These results demonstrate that this ML approach is interpretable and feasible for the design of advanced FNAs with high B_(s)and low H_(c).展开更多
SmCo based films with excellent intrinsic magnetic properties have promising applications in micro-electro-mechanical system(MEMS).However,due to the complexity of phase composition and uncontrollable crystallization ...SmCo based films with excellent intrinsic magnetic properties have promising applications in micro-electro-mechanical system(MEMS).However,due to the complexity of phase composition and uncontrollable crystallization degree of SmCo hard magnetic phase in the film,both the coercivity(Hc)and remanence(Mr)of films are difficult to enhance simultaneously.In this paper,SmCo based films were deposited with a Cr underlayer and capping layer on single crystal Si substrates via magnetron sputtering process.The effects of annealing parameters and Sm/Co atomic ratio on the phase structure and coercivity of films are discussed.By adjusting the Sm/Co atomic ratio from 1:5 to 1:4,Co soft magnetic phase disappears and the single phase SmCo5 is obtained,leading to the increase of coercivity of the films from 30 to 34 kOe.The influence of deposition temperature and Cu doping on magnetic properties of SmCo based films was investigated.When the deposition temperature increases from room temperature to 250℃,the coercivity will further increase from 34 to 51 kOe.However,a severe kink is observed in the demagnetization curves due to the poor exchanged coupling.An analysis of transmission electron microscopy(TEM)confirms that the average size of non-hard magnetic amorphous phase exceeds the effective exchanged coupling length of SmCo5,which contributes to the decoupling and low remanence ratio.Therefore,doping Cu and applying a post-annealing process can significantly improve the crystallization degree of the films.Both the coercivity and the remanence ratio of the demagnetization curves are greatly enhanced.We propose a plausible strategy to prepare the SmCo based films with high coercivity and remanence ratio by temperature and chemical optimization,which can be utilized in high performed MEMS devices.展开更多
The traditional high-temperature annealing process is difficult to control the morphology and size of the crystallization phases in amorphous alloy systems with high ferromagnetic element content,lead-ing to mechanica...The traditional high-temperature annealing process is difficult to control the morphology and size of the crystallization phases in amorphous alloy systems with high ferromagnetic element content,lead-ing to mechanical brittleness and soft magnetic properties deterioration.Here,we developed a flexible-annealing technique and successfully achieved a fine nanocrystalline structure in a high-ferromagnetic-content system of(Fe_(0.8)Co_(0.2))_(85)Si_(2)B_(12)Cu_(0.8)Mo_(0.2).It is exciting that the(Fe_(0.8)Co_(0.2))_(85)Si_(2)B_(12)Cu_(0.8)Mo_(0.2) nanocrystalline alloy exhibits high Bs up to 1.88 T,low coercivity of 6.3 A m-1,as well as good plas-ticity.The excellent comprehensive properties are attributed to the controllable construction of di-luted amorphous-nanocrystalline structure,the rapid release of internal stress,and the suppression of relaxation-induced uniformity achieved by the flexible annealing process.The results provide a fast and new paradigm for the development of next-generation high-Bs soft magnetic materials.展开更多
The phase structure and magnetic properties of high-Co containing permanent magnets with high thermal stability have been systematically studied in this work.It is abnormal that the coercivity of annealed samples was ...The phase structure and magnetic properties of high-Co containing permanent magnets with high thermal stability have been systematically studied in this work.It is abnormal that the coercivity of annealed samples was slightly lower than that of sintered samples,while the coercivity was usually enhanced after annealing in conventional Nd–Fe–B samples.Further analysis showed that in addition to RE_(2)(Fe,Co)_(14)B main phase and RE-rich grain boundary phase,there were also new Co-rich magnetic phases located in the grain boundary.During annealing,the phase structures of high-Co containing magnets were readjusted,especially the increasing Co-rich magnetic phase and emerging RE-rich particles precipitated from the main phase.Eventually,the isolated RE-rich particles would act as the pinning center of the domain wall movement in demagnetization process.It was confirmed that the coercivity of annealed high-Co containing magnets was controlled by both nucleation and pinning.Pinning mechanism can partially compensate for the weakening of magnetic isolation due to increased Co-rich magnetic phase,which explained the moderate decrease in coercivity of annealed high-Co containing magnets.The discovery of new coercivity mechanism contributed to in-depth understanding of high-Co containing magnets.展开更多
Due to its large magnetocrystalline anisotropy field and high Curie temperature,SmCo-based magnets are irreplaceable in high-temperature applications,The hot-deformed SmCo-based magnets are especially attractive for t...Due to its large magnetocrystalline anisotropy field and high Curie temperature,SmCo-based magnets are irreplaceable in high-temperature applications,The hot-deformed SmCo-based magnets are especially attractive for their excellent corrosion resistance,making them more suitable for harsh environments.However,it is still challenging for hot-deformed SmCo-based magnets to obtain high magnetization and high coercivity simultaneously.Therefore,it is necessary to analyze the relationship between its microstructure and magnetic properties and explore its magnetic hardening mechanism to guide the further improvement of magnetic properties.In this paper,the anisotropic heterostructure SmCo_(5)magnet was prepared by combining large height-reduction and introducing a nano-grained Smrich phase.Strong c-axis texture,(BH)m of 16.1 MGOe,and H_(ci)of 9.6 kOe were obtained via the heterostructure with SmCo_(5)micron-grain and Sm-rich nano-scale precipitates.The magnetic domain observation and technical magnetization analysis demonstrate that the coe rcivity mechanism is dominated by nucleation.The results also show that the smooth and Sm-rich precipitated grain boundary provides weak pinning effects.It provides a reference for the development of high-pe rformance nanocrystalline SmCo_(5)magnets.展开更多
The effect of the Y spacer layer on the phase composition,coercivity,and magnetization reversal processes of La-Nd-Fe-B films has been investigated.The addition of a 10 nm Y spacer layer increases the coercivity of th...The effect of the Y spacer layer on the phase composition,coercivity,and magnetization reversal processes of La-Nd-Fe-B films has been investigated.The addition of a 10 nm Y spacer layer increases the coercivity of the film to 1.36 T at 300 K and remains 0.938 T at 380 K.As the thickness of the Y spacer layer increases,Y participates in the formation of the main phase in the film,and further regulates the formation of La-B phases.The results of the first-order reversal curve(FORC)and micromagnetic fitting show that the coercivity of all the films is dominated by nucleation mechanism.The c-axis preferred orientation,good magnetic microstructure parameters and the largest dipole interaction enhance the coercivity.Therefore,the introduction of the Y spacer layer can be an effective way to improve the coercivity of La-Nd-Fe-B film over a wide temperature range of 150 K-380 K.展开更多
The incorporation of the high-abundance rareearth element Y in(Nd,Y)-Fe-B sintered magnets offers an opportunity to reduce the cost of permanent magnetic materials,while promoting the balanced usage of rare-earth reso...The incorporation of the high-abundance rareearth element Y in(Nd,Y)-Fe-B sintered magnets offers an opportunity to reduce the cost of permanent magnetic materials,while promoting the balanced usage of rare-earth resources.However,the performance of(Nd,Y)-Fe-B magnets prepared using the conventional dual-main-phase(DMP)method undergoes significant degradation due to the strong diffusion ability of Y.To suppress the excessive diffusion of Y,this study presents a macroscopic lamellar magnet preparation scheme.Consequently,the micromagnetic simulations revealed that the multilayer magnets exhibited superior intrinsic performance compared to DMP magnets.Subsequently,the multilayer magnets were prepared by alternately stacking the 0%Y(0Y)and 30%Y(30Y)magnetic powders.The observed magnetic properties demonstrated that the coercvity of the three-layer magnet was~0.23 T higher than that of the DMP magnet,leading to improved coercivity stability at high temperatures.Furthermore,the microstructural observations and elemental analyses indicated the presence of a~200-μm-thick interface layer at the contact site between the 0Y and 30Y magnetic layers.Thus,the proposed approach effectively suppressed the excessive diffusion of Y in(Nd,Y)-Fe-B magnets,thereby enhancing the magnetic performance of the sintered magnets.展开更多
Grain boundary diffusion technique with TbH3 nanoparticles was applied to fabricate Tb-less sintered NdFe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematic...Grain boundary diffusion technique with TbH3 nanoparticles was applied to fabricate Tb-less sintered NdFe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet are improved by 112% and reduced by 26% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient（α） and the coercivity temperature coefficient（β） of the magnets are improved after diffusion treatment. Microstructure shows that Tb element enriches in the surface region of Nd2Fe（14）B grains and is expected to exist as（Nd,Tb）2Fe（14）B phase. Thus, the magneto-crystalline anisotropy field of the magnet improves remarkably. As a result, the sintered Nd-FeB magnets by grain boundary diffusion with TbH3 nanoparticles exhibit enhanced coercivity.展开更多
MM85Cu15(MM = La,Ce,Pr,Nd) eutectic alloys were added into the hot-deformed Nd-Fe-B magnets to enhance the coercivity.It is found that three endothermic peaks occur on the differential scanning calorimetry curve of th...MM85Cu15(MM = La,Ce,Pr,Nd) eutectic alloys were added into the hot-deformed Nd-Fe-B magnets to enhance the coercivity.It is found that three endothermic peaks occur on the differential scanning calorimetry curve of the MM-Cu melt-spun ribbons at 432.2,451.1 and 516.5℃.The peaks substantially correspond to three types of MM-Cu low-melting eutectic phase.The coercivity of magnets increases when the MM-Cu content is lower than 4 wt%,and then keeps almost no change with the content further increasing to 5 wt%.The coercivity of the hot-deformed magnets with 4 wt% and without MM-Cu addition is 948 and 683 kA/m,respectively.Nearly all the platelet-shaped grains are isolated by the thickened intergranular phase after MM-Cu addition.Moreover,the average grain size of the magnets with MM-Cu addition decreases compared with that of the magnet without MM-Cu addition.Scanning electron microscopy images show that the areal fraction of the RE-rich grain boundary phase increases from 8.6% to 15.1% after MM-Cu addition.The La,Ce together with Cu and Ga aggregate at the grain boundary regions separating neighboring grains and smoothing the grain boundaries.Therefore,both the thickened grain boundary and decreased mean grain size result in the enhancement of coercivity after MM-Cu eutectic alloy addition.展开更多
It is confirmed that phase homogenization is very important for improving the magnetic properties of 2:17-type Sm-Co sintered magnets,In this work,the influence of solid solution process on microstructure and magnetic...It is confirmed that phase homogenization is very important for improving the magnetic properties of 2:17-type Sm-Co sintered magnets,In this work,the influence of solid solution process on microstructure and magnetic properties of the Sm(CobalFe0.233Cu0.073Zr0.024)7.6 sintered magnets was systematically studied.With the solid-solution treating duration(tS)increasing from 0 to 4 h,intrinsic coercivity(Hcj)increases from 12.83 to 36.54 kOe,magnetic field at knee-point(Hknee)increases from2.76 to 19.14 kOe,and the maximum energy product increases from 19.79 to 29.48 MGOe.The electron probe microanalyzer results reveal that there mainly exist gray and dark regions besides"white"rare earth-rich phase,and the conte nt of Sm,Fe and Cu elements for the two kinds of regions changes a lot for the specimens,Furthermore,with tS increasing up to 4 h,the elements content deviation between the gray and dark regions becomes small gradually from 3.94 at%to 0.27 at%,7.66 at%to 0.21 at%and 7.27 at%to 0.16 at%for Sm,Fe and Cu elements,respectively.Moreover,transmission electron microscopy results show that the distribution of cell size is much more concentrated for aged specimens when tS is 4 h.It is also found that the Cu concentration at cell boundaries for the 4 h solid-solution treatment case shows relatively higher values and greater concentration gradient(1.94 at%/nm).It is verified that sufficient solution treatment duration is prerequisite to form these homogeneous microstructural features,which are the key points for obtaining both high Hcj and Hknee.展开更多
The double-alloy powder mixed method is very proper for developing new small-mass products by changing the composi- tion of sintered Nd-Fe-B magnets, and there is little research on this aspect. The variation on magne...The double-alloy powder mixed method is very proper for developing new small-mass products by changing the composi- tion of sintered Nd-Fe-B magnets, and there is little research on this aspect. The variation on magnetic and mechanical properties of high intrinsic coercivity Nd-Fe-B magnets prepared by double-alloy powder mixed method was discussed, which is a method blend- ing two-type main phase alloy powders with different components. The results showed that the intrinsic coercivity and density of sin- tered Nd-Fe-B magnets increased gradually with the increase in Dy content, and the double-alloy powder mixed method could obtain high intrinsic coercivity Nd-Fe-B magnets with good crystallographic alignment and microstructure. The bending strength of sintered Nd-Fe-B magnets declined, and the Rockwell hardness of sintered Nd-Fe-B magnets first declined, and then increased with the in- crease in Dy content. The microstructure showed that there existed the phenomenon that the Dy element diffused into main phase dur- ing sintering process, and the distribution of Dy content in main phase had some variation in homogeneity as a result of incomplete reaction between the double-alloy powder types.展开更多
Nd-Fe-B permanent magnets with a small amount of A1 nano-particles doping were prepared by conventional sintered method. Effect of AI content on magnetic property, corrosion resistance and oxidation properties of the ...Nd-Fe-B permanent magnets with a small amount of A1 nano-particles doping were prepared by conventional sintered method. Effect of AI content on magnetic property, corrosion resistance and oxidation properties of the magnets were studied. Inves- tigation showed that the coercivity rose gradually, while the remanence decreased simultaneously with increase of A1 doping amount. Further investigation revealed that most A1 element diffused into the main phase and some A1 element diffused into the Nd-rich phase The autoclave test results showed that the corrosion rate of the magnets decreased with A1 content increasing. After oxidation, the maximum energy product losses of the magnets with 0.0 wt.% and 0.2 wt.% AI nano-particles doping were 6.13% and 3.99%, respec- tively. Therefore, A1 nano-particles doping was a promising way to enhance the coercivity and corrosion resistance of sintered Nd-Fe-B magnet.展开更多
The effects of Tb addition on the microstructure and magnetic properties of the NdFeB magnets prepared by HD method were investigated by X-ray diffraction(XRD) and BH magnetometers.The results of the microstructure sh...The effects of Tb addition on the microstructure and magnetic properties of the NdFeB magnets prepared by HD method were investigated by X-ray diffraction(XRD) and BH magnetometers.The results of the microstructure showed that both the Tb-doped and undoped permanent magnets were composed mostly of Tetragonal phase Nd2Fe14B(space group P42/mnm) and a trace amount of Nd-rich phase.Accordingly,addition of Tb led to a decrease of the pole density factor of(004),(006) and(008) crystal plane of the Nd2Fe14B phase calculated by Horta formula,but the coercivity of the magnets increased from 2038 kA/m up to 2302 kA/m as a consequence of Tb addition.The study of the Hc(T)/Ms(T) versus/Ms(T) behavior showed that the nucleation was the dominating mechanism for the magnetization reversal in both sintered magnets,and the microstructural parameters of αk and Neff were obtained also.The Kronmüller-plot showed an increase of the αk responsible for an increase of the coercivity.展开更多
Nd-Fe-B permanent magnets with a small amount of Cu nano-particles doping have been prepared by con-ventional sintered method. Effects of Cu content on magnetic properties, corrosion resistance, and oxidation properti...Nd-Fe-B permanent magnets with a small amount of Cu nano-particles doping have been prepared by con-ventional sintered method. Effects of Cu content on magnetic properties, corrosion resistance, and oxidation properties of the magnets have been studied. It shows that the coercivity rises gradually, while the remanence decreases simultaneously with increasing Cu doping amount. Microstructure observation reveals that Cu ele- ment enriches mainly the Nd-rich phase. Autoclave test results show that the corrosion rate of the magnets decreases with increasing Cu content. After oxidation, the maximum energy product loss of the magnets with 0 and 0.2 wt% Cu nano-particles doping are 6.13% and 0.g9%, respectively. Therefore, it is concluded that Cu nano-particles doping is a promising way to enhance the coercivity and corrosion resistance of sintered Nd-Fe-B magnets.展开更多
An N38SH-grade magnet with low oxygen content was used to study the evolution of magnetic properties upon post-sin-tering annealing. Phase transformation of as-sintered magnet was investigated by differential scanning...An N38SH-grade magnet with low oxygen content was used to study the evolution of magnetic properties upon post-sin-tering annealing. Phase transformation of as-sintered magnet was investigated by differential scanning calorimetry （DSC）. Three low temperature eutectic transition points were detected. Little change could be found when annealed below the lowest eutectic transition point. A wide annealing temperature range （460–560 oC） between the lowest and highest eutectic transition point was available for this magnet to achieve a relatively high coercivity （~1671 kA/m） at a relatively low Dy content （~3 wt.%）. However, squareness fac-tor （SF） of the demagnetizing curve and its temperature stability were found to decrease after annealing above the highest eutectic transition point. This was attributed to the change of Cu content in the Nd-rich phase under different annealing temperatures.展开更多
The effects of Nb on the thermal stability and impact toughness of ultra-high intrinsic coercivity of Nd-Fe-B magnets were investigated.The results showed that the addition of Nb could improve the thermal stability,an...The effects of Nb on the thermal stability and impact toughness of ultra-high intrinsic coercivity of Nd-Fe-B magnets were investigated.The results showed that the addition of Nb could improve the thermal stability,and obviously increased the impact toughness of sintered Nd-Fe-B magnets.The optimum thermal stability of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.0 at.%.The maximum impact toughness of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.5 at.%,but the magnetic properties of sintered Nd-Fe-B magnets drastically deteriorated when the content of Nb increased from 1.0 at.% to 1.5 at.%.The microstructure showed that overfull Nb addition made many ultra-fine grains get together,which led to the density of sintered Nd-Fe-B magnets decline and drastically deteriorated the magnetic properties of sintered Nd-Fe-B magnets.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52261037,52088101)the Key research project of Jiangxi Province(No.20203ABC28W006)the Double-Thousand Plan of Jiangxi Province(No.jxsq2023101057).
文摘The low coercivity is the major factor inhibiting the large-scale commercial utilization of Nd-Ce-Fe-B sintered magnets.In this work,we achieved a record-high coercivity of 15.04 kOe in Ga-doped Nd-Ce-Fe-B sintered magnets with 30 wt%Ce replacing Nd,demonstrating enormous potential.The Ga-doped Nd-Ce-Fe-B magnets with higher boron(HB)and lower boron(LB)content are designed.The coercivity of the HB magnet increases slightly from 10.80 to 12.26 kOe after annealing,attributed to the optimized distribution of grain boundary(GB)phases.In contrast,the coercivity of the LB magnet remarkably increases from 8.13 to 15.04 kOe after annealing.Microstructural observations indicate that the narrow GB phase in the as-sintered magnet is rich in Fe,and the strong exchange coupling of adjacent grains resulted in low coercivity.The evolution of Ga-rich phases reveals a potential formation mechanism of the RE_(6)Fe_(13)Ga phase,that is the RE-Fe amorphous phase and REGa phase in the as-sintered magnet combine to form the RE_(6)Fe_(13)Ga phase and RE-Ga amorphous phase during post-sinter annealing(RE:rare earth).Moreover,the GB phase of the annealed magnet transforms into a Fe-lean phase with a thickness of 16.4 nm.Magnetization and demagnetization behavior characterizations reveal that the exchange decoupling of adjacent grains induced by the optimized GB phases is the main reason for the remarkable coercivity enhancement,which is also validated by micromagnetic simulations.
基金supported by the National Natural Science Foundation of China(Nos.U21A2052,52071143 and 52301237)Guangdong Basic and Applied Basic Research Foundation(Nos.2023A1515010431 and 2022A1515011453)+1 种基金China Postdoctoral Science Foundation funded project(No.2022M720845)GDAS Project of Science and Technology Development(Nos.2022GDASZH-2022010104 and 2023GDASZH-2023010104)。
文摘Nanocrystalline Ce-based rare earth(RE)-Fe-B alloys exhibit relatively good hard magnetic properties and high performance-cost ratio,but their properties deteriorate seriously after hot deformation(HD).Here,we present a simplified one-step HD process for preparing anisotropic Ce-based Ce_(25.88)La_(2.85)Y_(4.56)Fe_(65.73)B_(0.98)(wt%)magnets.The precursor of nanocrystalline powders is first compacted inside a copper tube,and then the powders with the tube are deformed together to achieve magnetic anisotropy.Compared with the conventional two-step HD magnet,i.e.,hot pressing followed by HD,one-step HD significantly increased the coercivity from 1.6 to 3.0 kOe,and the maximum magnetic energy product was improved from 3.7 to 4.8 MGOe.The microstructure characterization indicates that one-step HD can not only produce a more desirable microstructure,characterized by well-aligned platelet-shaped grains with reduced aspect ratio but also greatly inhibit the formation of coarse grain(CG)region.Both of them have been confirmed to be beneficial to enhancing coercivity by micromagnetic simulations.Our results thus demonstrate that the simplified one-step HD process offers a promising approach to developing high-performance anisotropic Ce-based magnets.
基金Project supported by the National Key Research and Development Program of China(2022YFB3503403)the Inner Mongolia Major Technology Project(2021ZD0035)+1 种基金the Ningbo Natural Science Foundation(2023J343)the Science and Technology Innovation 2025 Major Project of Ningbo(2022Z106)。
文摘In this study,to enhance the coercivity and high-temperature stability of hot-deformed PrNd-Fe-B magnets,the NdHoAlGa alloy was utilized as a diffusion source and a dual-alloy diffusion process was employed to enhance the room temperature coercivity from 1.72 to 2.28 T.For the magnet doped with7 wt%Nd_(72.3)Ho_(13).8Al_(2.3)Ga_(11.7),within the temperature range from 20 to 200℃,the remanence temperature coefficient a increases from-0.16%/℃to-0.14%/℃,and the coercivity temperature coefficientβincreases from-0.49%/℃to-0.43%/℃.By controlling grain boundary(GB)phases and optimizing the main phase simultaneously,Ga was induced to motivate the formation of non-ferromagnetic GB phases,reducing the size of grains and intergranular exchange coupling.Additionally,Ho was diffused into the main phase,forming(Pr,Nd,Ho)-Fe-B phase,which enhances the magnetic crystalline anisotropy field of the main phase grains at high temperatures.
基金supported by the Research and Innovation Centre,Khulna University(KURC ID-47/2020)。
文摘Spinel cubic ferrites have huge applications in me mory and high frequency devices.For the improvement of these modern devices,the magnetic coercivity,permeability,and dielectric properties of a ferrite are the important issues.This article focuses on improving the magnetic coercivity,magnetic permeability,and dielectric properties of Co_(0.2)Zn_(0.3)Ni_(0.5)Eu_(x)Fe_(2-x)O_(4) ferrites,where x=0.00,0.06,and 0.10.The X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscopy(FESEM),energy dispersive X-ray(EDX),vibrating sample magnetometer(VSM),and an impedance analyzer were used to characterize the structural,magnetic,and dielectric properties of the samples.The XRD patterns indicate the formation of spinel cubic structure of the samples with a secondary peak(EuFeO_(3))for Eu doped samples.The densities and porosities of the samples follow an inverse trend,where the doped samples’lattice parameters are increased with the increment of rare earth Eu concentration.The FTIR analysis also proves the spinel cubic phase of the samples.The average grain size of the ferrites is obtained via FESEM images,and it is increased from 121 to 198 nm.VSM analysis confirms that doping of the Eu content also changes other hysteresis loop properties of Co_(0.2)Zn_(0.3)Ni_(0.5)Eu_(x)Fe_(2-x)O_(4) ferrites.Particularly,the coercivity of the Eu doped samples is greater than that of the mother alloy(x=0.00).The EDX study shows that there is no impurity contamination in the ferrites.The permeability and dielectric measurements show an improved quality factor of the Eu-doped samples with low magnetic and dielectric losses.Frequency dependent resistivity and impedance analysis also show the improved nature.From the observed properties of the samples,all the investigated ferrites might be strong candidates for potential applications in memory devices,magnetic sensors,and high frequency applications.
基金supported by the National Key R&D Program of China(Grant No.2022YFB2404101)the“Pioneer”R&D Programof Zhejiang Province(No.2023C01075)+1 种基金the Youth Innovation Promotion Association CAS(Grant No.2021294)the Ningbo Natural Science Foundation(No.2021J197).
文摘Overcoming the trade-offbetween saturation magnetic induction(B_(s))and coercivity(H_(c))of Fe-based nanocrystalline alloys(FNAs)remains a great challenge due to the traditional design relying on trial-anderror methods,which are time-consuming and inefficient.Herein,we present an interpretable machine learning(ML)algorithm for the effective design of advanced FNAs with improved B_(s)and low H_(c).Firstly,the FNAs datasets were established,consisting of 20 features including chemical composition,process parameters,and theoretically calculated parameters.Subsequently,a three-step feature selection was used to screen the key features that affect the B_(s)and H_(c)of FNAs.Among six different ML algorithms,extreme gradient boosting(XGBoost)performed the best in predicting B_(s)and H_(c).We further revealed the association of key features with B_(s)and H_(c)through linear regression and SHAP analysis.The valence electron concentration without Fe,Ni,and Co elements(VEC1)and valence electron concentration(VEC)ranked as the most important features for predicting B_(s)and H_(c),respectively.VEC1 had a positive impact on B_(s)when VEC1<0.78,while VEC had a negative effect on H_(c)when VEC<7.12.Optimized designed FNAs were successfully prepared,and the prediction errors for B_(s)and H_(c)are lower than 2.3%and 18%,respectively,when comparing the predicted and experimental results.These results demonstrate that this ML approach is interpretable and feasible for the design of advanced FNAs with high B_(s)and low H_(c).
基金Project supported by the National Key R&D Program of China(2022YFB3505700,2022YFB3807900)National Natural Science Foundation of China(51901079)+2 种基金R&D(Research and Development)Plan in Key Areas of Guangdong Province(SDZX2021002,212021032611700001)Natural Science Foundation of Guangdong Province(2020A1515010736,2021A1515010451)the Guangzhou Municipal Science and Technology Program(202007020008)。
文摘SmCo based films with excellent intrinsic magnetic properties have promising applications in micro-electro-mechanical system(MEMS).However,due to the complexity of phase composition and uncontrollable crystallization degree of SmCo hard magnetic phase in the film,both the coercivity(Hc)and remanence(Mr)of films are difficult to enhance simultaneously.In this paper,SmCo based films were deposited with a Cr underlayer and capping layer on single crystal Si substrates via magnetron sputtering process.The effects of annealing parameters and Sm/Co atomic ratio on the phase structure and coercivity of films are discussed.By adjusting the Sm/Co atomic ratio from 1:5 to 1:4,Co soft magnetic phase disappears and the single phase SmCo5 is obtained,leading to the increase of coercivity of the films from 30 to 34 kOe.The influence of deposition temperature and Cu doping on magnetic properties of SmCo based films was investigated.When the deposition temperature increases from room temperature to 250℃,the coercivity will further increase from 34 to 51 kOe.However,a severe kink is observed in the demagnetization curves due to the poor exchanged coupling.An analysis of transmission electron microscopy(TEM)confirms that the average size of non-hard magnetic amorphous phase exceeds the effective exchanged coupling length of SmCo5,which contributes to the decoupling and low remanence ratio.Therefore,doping Cu and applying a post-annealing process can significantly improve the crystallization degree of the films.Both the coercivity and the remanence ratio of the demagnetization curves are greatly enhanced.We propose a plausible strategy to prepare the SmCo based films with high coercivity and remanence ratio by temperature and chemical optimization,which can be utilized in high performed MEMS devices.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research,China(Grant No.2019B030302010)the Guangdong Basic and Applied Baic Research,China(Grant No.2020B1515130007)+2 种基金the Key Research and Development Plan of Dongguan,China(Grant No.20221200300062)the National Natural Science Foundation of China(Grant Nos.52192602,52071222,52101191,52171149)the National Key Research and Development Program of China(Grant No.2021YFA0716302).
文摘The traditional high-temperature annealing process is difficult to control the morphology and size of the crystallization phases in amorphous alloy systems with high ferromagnetic element content,lead-ing to mechanical brittleness and soft magnetic properties deterioration.Here,we developed a flexible-annealing technique and successfully achieved a fine nanocrystalline structure in a high-ferromagnetic-content system of(Fe_(0.8)Co_(0.2))_(85)Si_(2)B_(12)Cu_(0.8)Mo_(0.2).It is exciting that the(Fe_(0.8)Co_(0.2))_(85)Si_(2)B_(12)Cu_(0.8)Mo_(0.2) nanocrystalline alloy exhibits high Bs up to 1.88 T,low coercivity of 6.3 A m-1,as well as good plas-ticity.The excellent comprehensive properties are attributed to the controllable construction of di-luted amorphous-nanocrystalline structure,the rapid release of internal stress,and the suppression of relaxation-induced uniformity achieved by the flexible annealing process.The results provide a fast and new paradigm for the development of next-generation high-Bs soft magnetic materials.
基金Project supported by National Key R&D Program of China(Grant No.2021YFB3803003)Youth Innovation Promotion Association CAS(Grant No.2023311).
文摘The phase structure and magnetic properties of high-Co containing permanent magnets with high thermal stability have been systematically studied in this work.It is abnormal that the coercivity of annealed samples was slightly lower than that of sintered samples,while the coercivity was usually enhanced after annealing in conventional Nd–Fe–B samples.Further analysis showed that in addition to RE_(2)(Fe,Co)_(14)B main phase and RE-rich grain boundary phase,there were also new Co-rich magnetic phases located in the grain boundary.During annealing,the phase structures of high-Co containing magnets were readjusted,especially the increasing Co-rich magnetic phase and emerging RE-rich particles precipitated from the main phase.Eventually,the isolated RE-rich particles would act as the pinning center of the domain wall movement in demagnetization process.It was confirmed that the coercivity of annealed high-Co containing magnets was controlled by both nucleation and pinning.Pinning mechanism can partially compensate for the weakening of magnetic isolation due to increased Co-rich magnetic phase,which explained the moderate decrease in coercivity of annealed high-Co containing magnets.The discovery of new coercivity mechanism contributed to in-depth understanding of high-Co containing magnets.
基金Project supported by the National Key Research and Development Program of China(2021YFB3500300)the National Natural Science Foundation of China(51931007,51871005,52201212,52271161)+1 种基金General Program of Science and Technology Development Project of Beijing Municipal Education Commission of China(KM201710005006)the Program of Top Disciplines Construction in Beijing(PXM2019_014204_500031)。
文摘Due to its large magnetocrystalline anisotropy field and high Curie temperature,SmCo-based magnets are irreplaceable in high-temperature applications,The hot-deformed SmCo-based magnets are especially attractive for their excellent corrosion resistance,making them more suitable for harsh environments.However,it is still challenging for hot-deformed SmCo-based magnets to obtain high magnetization and high coercivity simultaneously.Therefore,it is necessary to analyze the relationship between its microstructure and magnetic properties and explore its magnetic hardening mechanism to guide the further improvement of magnetic properties.In this paper,the anisotropic heterostructure SmCo_(5)magnet was prepared by combining large height-reduction and introducing a nano-grained Smrich phase.Strong c-axis texture,(BH)m of 16.1 MGOe,and H_(ci)of 9.6 kOe were obtained via the heterostructure with SmCo_(5)micron-grain and Sm-rich nano-scale precipitates.The magnetic domain observation and technical magnetization analysis demonstrate that the coe rcivity mechanism is dominated by nucleation.The results also show that the smooth and Sm-rich precipitated grain boundary provides weak pinning effects.It provides a reference for the development of high-pe rformance nanocrystalline SmCo_(5)magnets.
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFB3500303)the National Natural Science Foundation of China(Grant Nos.52031014 and 51971219).
文摘The effect of the Y spacer layer on the phase composition,coercivity,and magnetization reversal processes of La-Nd-Fe-B films has been investigated.The addition of a 10 nm Y spacer layer increases the coercivity of the film to 1.36 T at 300 K and remains 0.938 T at 380 K.As the thickness of the Y spacer layer increases,Y participates in the formation of the main phase in the film,and further regulates the formation of La-B phases.The results of the first-order reversal curve(FORC)and micromagnetic fitting show that the coercivity of all the films is dominated by nucleation mechanism.The c-axis preferred orientation,good magnetic microstructure parameters and the largest dipole interaction enhance the coercivity.Therefore,the introduction of the Y spacer layer can be an effective way to improve the coercivity of La-Nd-Fe-B film over a wide temperature range of 150 K-380 K.
基金financially supported by the National Natural Science Foundation of China(No.52201235)the Natural Science Foundation of Ningbo City(No.2022J308)+4 种基金the Science and Technology Program of Zhejiang Province(No.2024C01145)Ningbo Young Science and Technology Innovation Leading Talents(No.2023QL040)Kunpeng Plan of Zhejiang ProvinceNingbo Top Talent Programthe"Pioneer"and"Leading Goose"R&D Program of Zhejiang(No.2022C01020)。
文摘The incorporation of the high-abundance rareearth element Y in(Nd,Y)-Fe-B sintered magnets offers an opportunity to reduce the cost of permanent magnetic materials,while promoting the balanced usage of rare-earth resources.However,the performance of(Nd,Y)-Fe-B magnets prepared using the conventional dual-main-phase(DMP)method undergoes significant degradation due to the strong diffusion ability of Y.To suppress the excessive diffusion of Y,this study presents a macroscopic lamellar magnet preparation scheme.Consequently,the micromagnetic simulations revealed that the multilayer magnets exhibited superior intrinsic performance compared to DMP magnets.Subsequently,the multilayer magnets were prepared by alternately stacking the 0%Y(0Y)and 30%Y(30Y)magnetic powders.The observed magnetic properties demonstrated that the coercvity of the three-layer magnet was~0.23 T higher than that of the DMP magnet,leading to improved coercivity stability at high temperatures.Furthermore,the microstructural observations and elemental analyses indicated the presence of a~200-μm-thick interface layer at the contact site between the 0Y and 30Y magnetic layers.Thus,the proposed approach effectively suppressed the excessive diffusion of Y in(Nd,Y)-Fe-B magnets,thereby enhancing the magnetic performance of the sintered magnets.
基金financially supported by the National Natural Science Foundation of China(Nos.51001002 and 51371002)the National High Technology Research and Development Program of China(No.2012AA063201)+3 种基金the Key Program of Science and Technology Development Project of Beijing Municipal Education Commission(No.KZ201110005007)Jinghua Talents of Beijing University of TechnologyRixin Talents of Beijing University of Technologythe Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions
文摘Grain boundary diffusion technique with TbH3 nanoparticles was applied to fabricate Tb-less sintered NdFe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet are improved by 112% and reduced by 26% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient（α） and the coercivity temperature coefficient（β） of the magnets are improved after diffusion treatment. Microstructure shows that Tb element enriches in the surface region of Nd2Fe（14）B grains and is expected to exist as（Nd,Tb）2Fe（14）B phase. Thus, the magneto-crystalline anisotropy field of the magnet improves remarkably. As a result, the sintered Nd-FeB magnets by grain boundary diffusion with TbH3 nanoparticles exhibit enhanced coercivity.
基金the National Natural Science Foundation of China(51771055,51331003)Plan of National Key Research and Development(2016YFB0700903)。
文摘MM85Cu15(MM = La,Ce,Pr,Nd) eutectic alloys were added into the hot-deformed Nd-Fe-B magnets to enhance the coercivity.It is found that three endothermic peaks occur on the differential scanning calorimetry curve of the MM-Cu melt-spun ribbons at 432.2,451.1 and 516.5℃.The peaks substantially correspond to three types of MM-Cu low-melting eutectic phase.The coercivity of magnets increases when the MM-Cu content is lower than 4 wt%,and then keeps almost no change with the content further increasing to 5 wt%.The coercivity of the hot-deformed magnets with 4 wt% and without MM-Cu addition is 948 and 683 kA/m,respectively.Nearly all the platelet-shaped grains are isolated by the thickened intergranular phase after MM-Cu addition.Moreover,the average grain size of the magnets with MM-Cu addition decreases compared with that of the magnet without MM-Cu addition.Scanning electron microscopy images show that the areal fraction of the RE-rich grain boundary phase increases from 8.6% to 15.1% after MM-Cu addition.The La,Ce together with Cu and Ga aggregate at the grain boundary regions separating neighboring grains and smoothing the grain boundaries.Therefore,both the thickened grain boundary and decreased mean grain size result in the enhancement of coercivity after MM-Cu eutectic alloy addition.
基金Project supported by the National Key Research and Development Program of China(2016YFB0700903)the National Natural Science Foundation of China(5159088251401054)。
文摘It is confirmed that phase homogenization is very important for improving the magnetic properties of 2:17-type Sm-Co sintered magnets,In this work,the influence of solid solution process on microstructure and magnetic properties of the Sm(CobalFe0.233Cu0.073Zr0.024)7.6 sintered magnets was systematically studied.With the solid-solution treating duration(tS)increasing from 0 to 4 h,intrinsic coercivity(Hcj)increases from 12.83 to 36.54 kOe,magnetic field at knee-point(Hknee)increases from2.76 to 19.14 kOe,and the maximum energy product increases from 19.79 to 29.48 MGOe.The electron probe microanalyzer results reveal that there mainly exist gray and dark regions besides"white"rare earth-rich phase,and the conte nt of Sm,Fe and Cu elements for the two kinds of regions changes a lot for the specimens,Furthermore,with tS increasing up to 4 h,the elements content deviation between the gray and dark regions becomes small gradually from 3.94 at%to 0.27 at%,7.66 at%to 0.21 at%and 7.27 at%to 0.16 at%for Sm,Fe and Cu elements,respectively.Moreover,transmission electron microscopy results show that the distribution of cell size is much more concentrated for aged specimens when tS is 4 h.It is also found that the Cu concentration at cell boundaries for the 4 h solid-solution treatment case shows relatively higher values and greater concentration gradient(1.94 at%/nm).It is verified that sufficient solution treatment duration is prerequisite to form these homogeneous microstructural features,which are the key points for obtaining both high Hcj and Hknee.
基金Project supported by the Natural Science Foundation of Hubei Province(2014CFB626,2015CFC785)the Research Project of Hubei Provincial Department of Education(D20151801)the Opening Foundation of Hubei Key Laboratory of Automotive Power Train and Electronic Control(ZDK1201404)
文摘The double-alloy powder mixed method is very proper for developing new small-mass products by changing the composi- tion of sintered Nd-Fe-B magnets, and there is little research on this aspect. The variation on magnetic and mechanical properties of high intrinsic coercivity Nd-Fe-B magnets prepared by double-alloy powder mixed method was discussed, which is a method blend- ing two-type main phase alloy powders with different components. The results showed that the intrinsic coercivity and density of sin- tered Nd-Fe-B magnets increased gradually with the increase in Dy content, and the double-alloy powder mixed method could obtain high intrinsic coercivity Nd-Fe-B magnets with good crystallographic alignment and microstructure. The bending strength of sintered Nd-Fe-B magnets declined, and the Rockwell hardness of sintered Nd-Fe-B magnets first declined, and then increased with the in- crease in Dy content. The microstructure showed that there existed the phenomenon that the Dy element diffused into main phase dur- ing sintering process, and the distribution of Dy content in main phase had some variation in homogeneity as a result of incomplete reaction between the double-alloy powder types.
基金Project supported by National Natural Science Foundation of China(51001002)Research Fund for the Doctoral Program of Higher Education of China(20091103120024)+3 种基金National High Technology Research and Development Program of China(2012AA063201)the Key Program of Science and Technology Development Project of Beijing Municipal Education Commission(KZ201110005007)the Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions211 Project of Beijing University of Technology and Rixin Talents of Beijing Universityof Technology for financial support
文摘Nd-Fe-B permanent magnets with a small amount of A1 nano-particles doping were prepared by conventional sintered method. Effect of AI content on magnetic property, corrosion resistance and oxidation properties of the magnets were studied. Inves- tigation showed that the coercivity rose gradually, while the remanence decreased simultaneously with increase of A1 doping amount. Further investigation revealed that most A1 element diffused into the main phase and some A1 element diffused into the Nd-rich phase The autoclave test results showed that the corrosion rate of the magnets decreased with A1 content increasing. After oxidation, the maximum energy product losses of the magnets with 0.0 wt.% and 0.2 wt.% AI nano-particles doping were 6.13% and 3.99%, respec- tively. Therefore, A1 nano-particles doping was a promising way to enhance the coercivity and corrosion resistance of sintered Nd-Fe-B magnet.
基金Project supported by the Key Project of the International Cooperation and Exchanges of the Zhejiang Province (2006C14014)the Provincial Science and Technology Project (2009C21010)+2 种基金the Provincial Natural Science Foundation (Z4090462 and Y6100640)the National Natural Science Foundation (51001092)the Foundation for University Young Teachers from the Ministry of Education of Zhejiang Province
文摘The effects of Tb addition on the microstructure and magnetic properties of the NdFeB magnets prepared by HD method were investigated by X-ray diffraction(XRD) and BH magnetometers.The results of the microstructure showed that both the Tb-doped and undoped permanent magnets were composed mostly of Tetragonal phase Nd2Fe14B(space group P42/mnm) and a trace amount of Nd-rich phase.Accordingly,addition of Tb led to a decrease of the pole density factor of(004),(006) and(008) crystal plane of the Nd2Fe14B phase calculated by Horta formula,but the coercivity of the magnets increased from 2038 kA/m up to 2302 kA/m as a consequence of Tb addition.The study of the Hc(T)/Ms(T) versus/Ms(T) behavior showed that the nucleation was the dominating mechanism for the magnetization reversal in both sintered magnets,and the microstructural parameters of αk and Neff were obtained also.The Kronmüller-plot showed an increase of the αk responsible for an increase of the coercivity.
基金supported by the National Natural Science Foundation of China (No. 51001002)the Research Fund for the Doctoral Program of Higher Education of China (No. 20091103120024)+2 种基金the National High Technology Research and Development Program of China (No.2012AA063201)the Key Program of Science and Technology Development Project of Beijing Municipal Education Commission (No. KZ201110005007)211 Project of Beijing University of Technology and Rixin Talents of Beijing University of Technology
文摘Nd-Fe-B permanent magnets with a small amount of Cu nano-particles doping have been prepared by con-ventional sintered method. Effects of Cu content on magnetic properties, corrosion resistance, and oxidation properties of the magnets have been studied. It shows that the coercivity rises gradually, while the remanence decreases simultaneously with increasing Cu doping amount. Microstructure observation reveals that Cu ele- ment enriches mainly the Nd-rich phase. Autoclave test results show that the corrosion rate of the magnets decreases with increasing Cu content. After oxidation, the maximum energy product loss of the magnets with 0 and 0.2 wt% Cu nano-particles doping are 6.13% and 0.g9%, respectively. Therefore, it is concluded that Cu nano-particles doping is a promising way to enhance the coercivity and corrosion resistance of sintered Nd-Fe-B magnets.
基金Project supported by the National Natural Science Foundation of China(51171111)
文摘An N38SH-grade magnet with low oxygen content was used to study the evolution of magnetic properties upon post-sin-tering annealing. Phase transformation of as-sintered magnet was investigated by differential scanning calorimetry （DSC）. Three low temperature eutectic transition points were detected. Little change could be found when annealed below the lowest eutectic transition point. A wide annealing temperature range （460–560 oC） between the lowest and highest eutectic transition point was available for this magnet to achieve a relatively high coercivity （~1671 kA/m） at a relatively low Dy content （~3 wt.%）. However, squareness fac-tor （SF） of the demagnetizing curve and its temperature stability were found to decrease after annealing above the highest eutectic transition point. This was attributed to the change of Cu content in the Nd-rich phase under different annealing temperatures.
基金supported by the National High Technology Research and Development Program of China(2007AA03Z438)the National Natural Science Foundations of China(50871032)
文摘The effects of Nb on the thermal stability and impact toughness of ultra-high intrinsic coercivity of Nd-Fe-B magnets were investigated.The results showed that the addition of Nb could improve the thermal stability,and obviously increased the impact toughness of sintered Nd-Fe-B magnets.The optimum thermal stability of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.0 at.%.The maximum impact toughness of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.5 at.%,but the magnetic properties of sintered Nd-Fe-B magnets drastically deteriorated when the content of Nb increased from 1.0 at.% to 1.5 at.%.The microstructure showed that overfull Nb addition made many ultra-fine grains get together,which led to the density of sintered Nd-Fe-B magnets decline and drastically deteriorated the magnetic properties of sintered Nd-Fe-B magnets.
