The intermetallic compounds based on the tetragonal ThMn_(12) prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properti...The intermetallic compounds based on the tetragonal ThMn_(12) prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properties.However,the trade-off between the phase stability and the magnetic performance is often encountered in the ThMn_(12)-type magnets.This work was focused on the effects of V doping and nanos-tructuring on the phase stability and magnetic properties of ThMn_(12)-type Sm-Co-based magnets.Novel SmCo_(12)-based nanocrystalline alloys with the SmCo_(12) main phase were prepared for the first time.The prepared alloys from the optimal design achieved obviously higher coercivity than the isotropic SmFe_(12)-based alloys,together with comparable performance of other magnetic features.The enhancement in the coercivity was ascribed to the pinning of domain walls by the nanocrystalline grain boundaries and stacking faults.First-principles calculations and magnetic structure analysis disclosed that V substitution can stabilize the SmCo_(12) lattice and elevate its magnetocrystalline anisotropy.This study provides a new approach to developing stabilized metastable structured rare-earth-lean alloys with high magnetic per-formance.展开更多
Three types of NdFeB magnets with the same composition and different grain sizes were prepared,and then the grain boundary diffusion was conducted using metal Tb under the same technical parameters.The effect of grain...Three types of NdFeB magnets with the same composition and different grain sizes were prepared,and then the grain boundary diffusion was conducted using metal Tb under the same technical parameters.The effect of grain size on the grain boundary diffusion process and properties of sintered NdFeB magnets was investigated.The diffusion process was assessed using X-ray diffractometer,field emission scanning electron microscope,and electron probe microanalyzer.The magnetic properties of the magnet before and after diffusion were investigated.The results show that the grain refinement of the magnet leads to higher Tb utilization efficiency and results in higher coercivity at different temperatures.It can be attributed to the formation of a deeper and more complete core-shell structure,resulting in better magnetic isolation and higher anisotropy of the Nd_(2)Fe_(14)B grains.This work may shed light on developing high coercivity with low heavy rare earth elements through grain refinement.展开更多
Hexaferrites'magnetic and structural properties are highly sensitive to changes in sintering temperature and cationic replacements.We fabricated Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)hexaferrites using the sol-gel tec...Hexaferrites'magnetic and structural properties are highly sensitive to changes in sintering temperature and cationic replacements.We fabricated Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)hexaferrites using the sol-gel technique.We examined the phase,microstructure and magnetic aspects of the samples with respect to varying doping of rare earth dysprosium.The results show the expansion in the lattice upon incorporation of dysprosium against iron.Morphological studies confirm the uniform distribution of particles with slightly longitudinal nanoflakes in one direction.Magnetic investigations show an increase in magnetic saturation(Ms)with increasing dysprosium incorporation till optimum level is achieved for 15%doping concentration,with negligible change for maximum doping level.Furthermore,coercivity(Hc)and magnetic moment(mB)in terms of Bohr's magneton(μB)also show an increasing trend with dysprosium substitution levels.The maximum saturation magnetization of 33.355 emu/g is achieved with magnetic remanence of 18.290 emu/g,along with optimum magnetic moment of 6.249μB.In addition to the traditional magnetic parameters,magnetic anisotropy parameters were explored for the deep insights into magnetic parameters.These outcomes suggest that improved magnetic properties of Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)ferrites make it good substitute for storage devices,magnetic filters,and other magnetic applications.展开更多
In this paper,the fracture behaviors and interface stresses of sintered Nd-Fe-B magnets were investigated.It was revealed that cracks propagated along the interfaces of Nd_(2)Fe_(14)B/Nd_(2)Fe_(14)B,Nd_(2)Fe_(14)B/Nd-...In this paper,the fracture behaviors and interface stresses of sintered Nd-Fe-B magnets were investigated.It was revealed that cracks propagated along the interfaces of Nd_(2)Fe_(14)B/Nd_(2)Fe_(14)B,Nd_(2)Fe_(14)B/Nd-rich phases and within Nd-rich phases.The misfits between 2:14:1 and Nd-rich phases were quantitatively determined,reflecting the concentration of interface stresses in magnet.Grain boundaries of magnet were reconstructed by diffusing Tb-containing and Tb-free sources,respectively.The Tb-rich shells at extensive layers of 2:14:1 grains caused lattice distortion,i.e.,internal stresses,resulting in the crack mode changing from intergranular to transgranular in near surfaces of Tb-containing diffused magnets.Therefore,the bending strengths were deteriorated although the coercivities were apparently enhanced.In the case of Tb-free Pr-Cu diffused magnet,the Pr and Cu elements were enriched at grain boundaries,and the misfits between 2:14:1 and Nd-rich phases were declined,lowering interface stresses and strengthening grain boundaries.The mechanical and magnetic properties of Pr-Cu diffused magnet were simultaneously improved.展开更多
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
In this work,the effect of the Al addition amount in the TbAl coatings on the grain boundary diffusion proces s(GBDP)of Tb were systematically explored.Direct current magnetron sputtering(DCMS)method was utilized in c...In this work,the effect of the Al addition amount in the TbAl coatings on the grain boundary diffusion proces s(GBDP)of Tb were systematically explored.Direct current magnetron sputtering(DCMS)method was utilized in co-sputtering manner to synthesize the TbAl coatings with certain Tb consumption and various Al addition amount.Results show that the moderate Al addition amount significantly improves the wettability of grain boundary(GB)phases,thereby acquiring more continuous and uniform Tb-rich shells and GB phases between matrix phases,as well as deeper diffusion depth and denser microstructure.The largest increase amplitude of intrinsic coercivity(Hcj)is improved by 78.4%in TbAIdiffused magnet compared to the pure Tb-diffused magnet,while the remanence(Br)is expected to show an overall decreasing tendency accompanied with a slight increase in the decreasing process.However,when the Al addition amount is excessive,magnetic dilution effect is enhanced,and the Tbrich shells and GB phases between matrix phases become fuzzy and even invisible,which in turn deteriorates the magnetic properties of diffused magnets.展开更多
The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr_(58)Dy_(10)Cu_(32)alloy was investigated through scanning electron microscope(SEM)and in-situ magneto-optic Kerr effect(MOKE)microscopy.The modi...The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr_(58)Dy_(10)Cu_(32)alloy was investigated through scanning electron microscope(SEM)and in-situ magneto-optic Kerr effect(MOKE)microscopy.The modification treatment resulted in the formation of a smooth and continuous weakly magnetic grain boundary layer and the(Nd,Pr,Dy)_(2)Fe_(14)B main phase with a high magnetocrystalline anisotropy field,leading to an increased coercivity of 23 kOe.MOKE observations revealed that the dynamic evolution of the maze domain area under an external magnetic field varied significantly between the original and modified magnets.Compared with the original magnets,the modified magnets exhibited a slower decrease in maze domain area during magnetization and a slower increase during reverse magnetization,contributing to the observed coercivity enhancement.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
We investigate a class of elliptic equations with an L^(1)source in the framework of variable exponent spaces.A key characteristic of these equations is the coexistence of a degenerate coercivity term and a lower-orde...We investigate a class of elliptic equations with an L^(1)source in the framework of variable exponent spaces.A key characteristic of these equations is the coexistence of a degenerate coercivity term and a lower-order convection term.By employing innovative integralbased test functions,we derive the necessary a priori estimates.To prove the convergence of solutions to the degenerate coercivity problem,we adopt a method that combines monotonicity and truncation techniques.This approach allows us to demonstrate that the gradient sequences converge almost everywhere.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
SmFe_(12)-based alloys perform promising potential for new generation permanent magnets,attributed to their high saturation magnetization(Ms)and anisotropy field(Ha).Introduction of the low melting point element Cu ca...SmFe_(12)-based alloys perform promising potential for new generation permanent magnets,attributed to their high saturation magnetization(Ms)and anisotropy field(Ha).Introduction of the low melting point element Cu can promote the formation of non-magnetic grain boundaries in Sm-Fe-Ti system.The effect of Cu content on the grain boundary phase formation and magnetic properties in Sm(Fe_(0.8)Co_(0.2))_(11-x)TiCu_(x)(x=0-0.5)strips has been investigated.Sm(Fe_(0.8)Co_(0.2))_(10.8)TiCu_(0.2) strip exhibited a maximum Ms value of 1.07 T.Coercivity improved from 20.96 kA m^(-1) for Sm(Fe_(0.8)Co_(0.2))_(11)Ti strip to 165.92 kA m^(-1) for Sm(Fe_(0.8)Co_(0.2))_(10.5)TiCu_(0.5) strip.When Cu content increased from 0 to 0.5 at.%,Fe content of the grain boundary phase decreased from 43.8 to 12.6 at.%.Due to the good wettability of Cu,main 1:12 phase is well isolated and enveloped by(Sm,Cu)-rich grain boundary phase.Cu addition facilitates the formation of the continuous non-magnetic grain boundaries and reduces grain size of main 1:12 phase,contributing to coercivity improvement of the strips.展开更多
Pd/Co_(2)MnSi(CMS)/Co/Pd multilayer films were designed based on the idea of combining highly spin-polarized materials with strong perpendicular magnetic anisotropy(PMA)films.The PMA of Pd/CMS/Co/Pd multilayer films w...Pd/Co_(2)MnSi(CMS)/Co/Pd multilayer films were designed based on the idea of combining highly spin-polarized materials with strong perpendicular magnetic anisotropy(PMA)films.The PMA of Pd/CMS/Co/Pd multilayer films was studied by optimizing the growth conditions and thickness of each film layer.The optimal structure of the multilayer films was Pd(6 nm)/CMS(5 nm)/Co(2 nm)/Pd(1 nm).Its abnormal Hall resistance(R_(Hall)),coercivity(H_(c))and effective magnetic anisotropy constant(Keff)are 0.08Ω,284 Oe and 1.36 Merg/cm^(3),respectively,which are 100%,492%,and 183%higher than the corresponding values(0.04Ω,48 Oe,and 0.48 Merg/cm^(3))of the Pd(6 nm)/Co(1 nm)/Pd(3 nm)trilayer films.The analysis shows that the increases of the above values are the result of the Pd/CMS interface effect and CMS/Co interface ferromagnetic(FM)coupling,and that it is closely related to the thickness of each film layer in the multilayer films and the growth conditions of the multilayer films.展开更多
The substitution of Fe by Co in the 2:14:1 phase is an effective method to increase the Curie temperature and enhance the thermal stability of the Nd-Fe-B magnets.However,the accumulation of Co ele ment at the grain b...The substitution of Fe by Co in the 2:14:1 phase is an effective method to increase the Curie temperature and enhance the thermal stability of the Nd-Fe-B magnets.However,the accumulation of Co ele ment at the grain boundaries(GBs) changes the GBs from nonmagnetic to ferromagnetic and causes the thinlayer GBs to become rare,In this paper,the method of diffusing Tb element was chosen to improve the microstructure and temperature stability of high-Co magnets.Three original sintered Nd_(28.5)Dy_(3)-CO_(x)e_(bal)M_(0.6)B_(i)(x=0,6 wt%,12 wt%;M = Cu,Al,Zr) magnets with different Co contents were diffused with Tb by grain boundary diffusion(GBD).After GBD,high-Co magnets exhibit more continuously distributed thin-layer GBs,and their thermal stability is significantly improved.In high-Co magnets(x=6 wt%),the absolute value of the temperature coefficient of coercivity decreases from 0.603%/K to0.508%/K in the temperature range of 293-413 K,that of remanence decreases from 0.099%/K to 0.091%/K,and the coercivity increases from 18.44 to 25.04 kOe.Transmission electron microscopy(TEM)characterization reveals that there are both the 1:2 phase and the amorphous phase in the high-Co magnet before and after GBD,EDS elemental analysis shows that Tb element is more likely to preferentially replace the rare earth elements in the 2:14:1 main phase than in the 1:2 phase and the amorphous phase.The concentration of Tb at the edge of the main phase is much higher than that in the 1:2phase and amorphous phase,which is beneficial to the improvement of the microstructure.The preferential replacement of Tb elements at the edge of the 2:14:1 phase and thin-layer GBs with a more continuous distribution are synergistically responsible for improving the thermal stability of high-Co magnets.The study indicates that GBD is an effective method to improve the microstructure and thermal stability of high-Co magnets.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
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
Grain boundary diffusion process(GBDP)is a widely used method of increasing the coercivity of sintered NdFeB magnets.In this study,the effects of the GBDP on the bending strength and microhardness of sintered NdFeB ma...Grain boundary diffusion process(GBDP)is a widely used method of increasing the coercivity of sintered NdFeB magnets.In this study,the effects of the GBDP on the bending strength and microhardness of sintered NdFeB magnets and the fracture mode were investigated.Results show that the bending strength of magnets is reduced by pickling and heat treatment and greatly recove rs after heavy rare earth element(Tb)grain boundary diffusion.The pickling and the heat treatment cause a slight decrease in microhardness.Compared with the recovery of the bending strength,the hardness decreases after the GBDP.The fracture mode of bended magnets changes from intergranular to transgranular.This study helps in further improving the mechanical and magnetic properties of sintered NdFeB magnets.展开更多
In current research work,Dy3+substituted Mg0.5Cu0.25Co0.25Fe2-xDyxO4(0.0≤x≤0.04 with the step interval of 0.01)soft ferrites were synthesized by the sol-gel auto combustion method.The prepared samples were character...In current research work,Dy3+substituted Mg0.5Cu0.25Co0.25Fe2-xDyxO4(0.0≤x≤0.04 with the step interval of 0.01)soft ferrites were synthesized by the sol-gel auto combustion method.The prepared samples were characterized by the techniques using X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),Fourier transform infrared(FTIR)spectroscopy,curre nt-voltage(Ⅰ-Ⅴ)measurement,LCR meter,vibrating sample magnetometer(VSM)and Raman.XRD data reveal that the average crystallite size is 49.71 nm and the lattice constant is 0.83703 nm for sample x=0.03.The non-uniform grain growth was demonstrated by micrographs and impurity-free elemental composition was observed from EDX analysis.The DC resistivity has an increasing and decreasing trend in ferromagnetic and paramagnetic regions with an increase in temperature.Moreover,the high resistivity is observed with the order of 1010Ω·cm,and the activation energy is 0.944 eV for samples x=0.03.The dielectric parameters including dielectric constant,dielectric losses,and impedance gradually decrease with the increase in frequency from 8 Hz to 8 MHz.The minimum dielectric loss at high frequency is found for sample x=0.03.The coercivity(Hc)and saturation magnetization(Ms)are found in the ranges of 520.82-544.02 Oe and 20.5841-21.1473 emu/g,respectively.These observations confirm that dysprosium(x=0.03)doped MCC-soft ferrites may be applicable in transformer cores,microwave absorbance,and telecommunication devices.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
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
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
基金supported by the National Key R&D Program of China(Nos.2021YFB3501502 and 2021YFB3501504).
文摘The intermetallic compounds based on the tetragonal ThMn_(12) prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properties.However,the trade-off between the phase stability and the magnetic performance is often encountered in the ThMn_(12)-type magnets.This work was focused on the effects of V doping and nanos-tructuring on the phase stability and magnetic properties of ThMn_(12)-type Sm-Co-based magnets.Novel SmCo_(12)-based nanocrystalline alloys with the SmCo_(12) main phase were prepared for the first time.The prepared alloys from the optimal design achieved obviously higher coercivity than the isotropic SmFe_(12)-based alloys,together with comparable performance of other magnetic features.The enhancement in the coercivity was ascribed to the pinning of domain walls by the nanocrystalline grain boundaries and stacking faults.First-principles calculations and magnetic structure analysis disclosed that V substitution can stabilize the SmCo_(12) lattice and elevate its magnetocrystalline anisotropy.This study provides a new approach to developing stabilized metastable structured rare-earth-lean alloys with high magnetic per-formance.
基金Key Research and Development Program of Shandong Province(2021CXGC010310)Shandong Province Science and Technology Small and Medium Sized Enterprise Innovation Ability Enhancement Project(2023TSGC0287,2024TSGC0519)+1 种基金Shandong Provincial Natural Science Foundation(ZR2022ME222)National Natural Science Foundation of China(51702187)。
文摘Three types of NdFeB magnets with the same composition and different grain sizes were prepared,and then the grain boundary diffusion was conducted using metal Tb under the same technical parameters.The effect of grain size on the grain boundary diffusion process and properties of sintered NdFeB magnets was investigated.The diffusion process was assessed using X-ray diffractometer,field emission scanning electron microscope,and electron probe microanalyzer.The magnetic properties of the magnet before and after diffusion were investigated.The results show that the grain refinement of the magnet leads to higher Tb utilization efficiency and results in higher coercivity at different temperatures.It can be attributed to the formation of a deeper and more complete core-shell structure,resulting in better magnetic isolation and higher anisotropy of the Nd_(2)Fe_(14)B grains.This work may shed light on developing high coercivity with low heavy rare earth elements through grain refinement.
基金the Deanship of Scientific Research at King Khalid University for funding this work through a large group Research Project under grant(RGP2/111/45)。
文摘Hexaferrites'magnetic and structural properties are highly sensitive to changes in sintering temperature and cationic replacements.We fabricated Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)hexaferrites using the sol-gel technique.We examined the phase,microstructure and magnetic aspects of the samples with respect to varying doping of rare earth dysprosium.The results show the expansion in the lattice upon incorporation of dysprosium against iron.Morphological studies confirm the uniform distribution of particles with slightly longitudinal nanoflakes in one direction.Magnetic investigations show an increase in magnetic saturation(Ms)with increasing dysprosium incorporation till optimum level is achieved for 15%doping concentration,with negligible change for maximum doping level.Furthermore,coercivity(Hc)and magnetic moment(mB)in terms of Bohr's magneton(μB)also show an increasing trend with dysprosium substitution levels.The maximum saturation magnetization of 33.355 emu/g is achieved with magnetic remanence of 18.290 emu/g,along with optimum magnetic moment of 6.249μB.In addition to the traditional magnetic parameters,magnetic anisotropy parameters were explored for the deep insights into magnetic parameters.These outcomes suggest that improved magnetic properties of Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)ferrites make it good substitute for storage devices,magnetic filters,and other magnetic applications.
基金supported by the National Natural Science Foundation of China(No.52271165)the National Key R&D Program of China(No.2022YFB3505501).
文摘In this paper,the fracture behaviors and interface stresses of sintered Nd-Fe-B magnets were investigated.It was revealed that cracks propagated along the interfaces of Nd_(2)Fe_(14)B/Nd_(2)Fe_(14)B,Nd_(2)Fe_(14)B/Nd-rich phases and within Nd-rich phases.The misfits between 2:14:1 and Nd-rich phases were quantitatively determined,reflecting the concentration of interface stresses in magnet.Grain boundaries of magnet were reconstructed by diffusing Tb-containing and Tb-free sources,respectively.The Tb-rich shells at extensive layers of 2:14:1 grains caused lattice distortion,i.e.,internal stresses,resulting in the crack mode changing from intergranular to transgranular in near surfaces of Tb-containing diffused magnets.Therefore,the bending strengths were deteriorated although the coercivities were apparently enhanced.In the case of Tb-free Pr-Cu diffused magnet,the Pr and Cu elements were enriched at grain boundaries,and the misfits between 2:14:1 and Nd-rich phases were declined,lowering interface stresses and strengthening grain boundaries.The mechanical and magnetic properties of Pr-Cu diffused magnet were simultaneously improved.
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Project supported by National Key Research and Development Program of China(2021YFB3500100)National Natural Science Foundation of China(52301068)。
文摘In this work,the effect of the Al addition amount in the TbAl coatings on the grain boundary diffusion proces s(GBDP)of Tb were systematically explored.Direct current magnetron sputtering(DCMS)method was utilized in co-sputtering manner to synthesize the TbAl coatings with certain Tb consumption and various Al addition amount.Results show that the moderate Al addition amount significantly improves the wettability of grain boundary(GB)phases,thereby acquiring more continuous and uniform Tb-rich shells and GB phases between matrix phases,as well as deeper diffusion depth and denser microstructure.The largest increase amplitude of intrinsic coercivity(Hcj)is improved by 78.4%in TbAIdiffused magnet compared to the pure Tb-diffused magnet,while the remanence(Br)is expected to show an overall decreasing tendency accompanied with a slight increase in the decreasing process.However,when the Al addition amount is excessive,magnetic dilution effect is enhanced,and the Tbrich shells and GB phases between matrix phases become fuzzy and even invisible,which in turn deteriorates the magnetic properties of diffused magnets.
基金supported by the National Key Research and Development Program of China(Grant Nos.2021YFB3500300,2023YFB3507000,and 2023XYJG0001-01-03)the National Natural Science Foundation of China(Grant No.52171167)Inner Mongolia Northern Rare Earth Advanced Materials Technology Innovation Co.,Ltd.Project(Grant No.CXZX-B-202304-0004).
文摘The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr_(58)Dy_(10)Cu_(32)alloy was investigated through scanning electron microscope(SEM)and in-situ magneto-optic Kerr effect(MOKE)microscopy.The modification treatment resulted in the formation of a smooth and continuous weakly magnetic grain boundary layer and the(Nd,Pr,Dy)_(2)Fe_(14)B main phase with a high magnetocrystalline anisotropy field,leading to an increased coercivity of 23 kOe.MOKE observations revealed that the dynamic evolution of the maze domain area under an external magnetic field varied significantly between the original and modified magnets.Compared with the original magnets,the modified magnets exhibited a slower decrease in maze domain area during magnetization and a slower increase during reverse magnetization,contributing to the observed coercivity enhancement.
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Supported by the National Natural Science Foundation of China(Grant No.11901131)。
文摘We investigate a class of elliptic equations with an L^(1)source in the framework of variable exponent spaces.A key characteristic of these equations is the coexistence of a degenerate coercivity term and a lower-order convection term.By employing innovative integralbased test functions,we derive the necessary a priori estimates.To prove the convergence of solutions to the degenerate coercivity problem,we adopt a method that combines monotonicity and truncation techniques.This approach allows us to demonstrate that the gradient sequences converge almost everywhere.
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.
文摘SmFe_(12)-based alloys perform promising potential for new generation permanent magnets,attributed to their high saturation magnetization(Ms)and anisotropy field(Ha).Introduction of the low melting point element Cu can promote the formation of non-magnetic grain boundaries in Sm-Fe-Ti system.The effect of Cu content on the grain boundary phase formation and magnetic properties in Sm(Fe_(0.8)Co_(0.2))_(11-x)TiCu_(x)(x=0-0.5)strips has been investigated.Sm(Fe_(0.8)Co_(0.2))_(10.8)TiCu_(0.2) strip exhibited a maximum Ms value of 1.07 T.Coercivity improved from 20.96 kA m^(-1) for Sm(Fe_(0.8)Co_(0.2))_(11)Ti strip to 165.92 kA m^(-1) for Sm(Fe_(0.8)Co_(0.2))_(10.5)TiCu_(0.5) strip.When Cu content increased from 0 to 0.5 at.%,Fe content of the grain boundary phase decreased from 43.8 to 12.6 at.%.Due to the good wettability of Cu,main 1:12 phase is well isolated and enveloped by(Sm,Cu)-rich grain boundary phase.Cu addition facilitates the formation of the continuous non-magnetic grain boundaries and reduces grain size of main 1:12 phase,contributing to coercivity improvement of the strips.
基金Project supported by Shandong Provincial Natural Science Foundation,China(Grant No.ZR2022ME059)。
文摘Pd/Co_(2)MnSi(CMS)/Co/Pd multilayer films were designed based on the idea of combining highly spin-polarized materials with strong perpendicular magnetic anisotropy(PMA)films.The PMA of Pd/CMS/Co/Pd multilayer films was studied by optimizing the growth conditions and thickness of each film layer.The optimal structure of the multilayer films was Pd(6 nm)/CMS(5 nm)/Co(2 nm)/Pd(1 nm).Its abnormal Hall resistance(R_(Hall)),coercivity(H_(c))and effective magnetic anisotropy constant(Keff)are 0.08Ω,284 Oe and 1.36 Merg/cm^(3),respectively,which are 100%,492%,and 183%higher than the corresponding values(0.04Ω,48 Oe,and 0.48 Merg/cm^(3))of the Pd(6 nm)/Co(1 nm)/Pd(3 nm)trilayer films.The analysis shows that the increases of the above values are the result of the Pd/CMS interface effect and CMS/Co interface ferromagnetic(FM)coupling,and that it is closely related to the thickness of each film layer in the multilayer films and the growth conditions of the multilayer films.
基金supported by the National Key R&D Program of China (2021YFB3502902,2021YFB3503100,2022YFB3503300,2022YFB3505200)。
文摘The substitution of Fe by Co in the 2:14:1 phase is an effective method to increase the Curie temperature and enhance the thermal stability of the Nd-Fe-B magnets.However,the accumulation of Co ele ment at the grain boundaries(GBs) changes the GBs from nonmagnetic to ferromagnetic and causes the thinlayer GBs to become rare,In this paper,the method of diffusing Tb element was chosen to improve the microstructure and temperature stability of high-Co magnets.Three original sintered Nd_(28.5)Dy_(3)-CO_(x)e_(bal)M_(0.6)B_(i)(x=0,6 wt%,12 wt%;M = Cu,Al,Zr) magnets with different Co contents were diffused with Tb by grain boundary diffusion(GBD).After GBD,high-Co magnets exhibit more continuously distributed thin-layer GBs,and their thermal stability is significantly improved.In high-Co magnets(x=6 wt%),the absolute value of the temperature coefficient of coercivity decreases from 0.603%/K to0.508%/K in the temperature range of 293-413 K,that of remanence decreases from 0.099%/K to 0.091%/K,and the coercivity increases from 18.44 to 25.04 kOe.Transmission electron microscopy(TEM)characterization reveals that there are both the 1:2 phase and the amorphous phase in the high-Co magnet before and after GBD,EDS elemental analysis shows that Tb element is more likely to preferentially replace the rare earth elements in the 2:14:1 main phase than in the 1:2 phase and the amorphous phase.The concentration of Tb at the edge of the main phase is much higher than that in the 1:2phase and amorphous phase,which is beneficial to the improvement of the microstructure.The preferential replacement of Tb elements at the edge of the 2:14:1 phase and thin-layer GBs with a more continuous distribution are synergistically responsible for improving the thermal stability of high-Co magnets.The study indicates that GBD is an effective method to improve the microstructure and thermal stability of high-Co magnets.
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Project supported by the National Key Research and Development Program of China(2021YFB3502902)the Key Research and Development Program of Ningbo(2021Z024)。
文摘Grain boundary diffusion process(GBDP)is a widely used method of increasing the coercivity of sintered NdFeB magnets.In this study,the effects of the GBDP on the bending strength and microhardness of sintered NdFeB magnets and the fracture mode were investigated.Results show that the bending strength of magnets is reduced by pickling and heat treatment and greatly recove rs after heavy rare earth element(Tb)grain boundary diffusion.The pickling and the heat treatment cause a slight decrease in microhardness.Compared with the recovery of the bending strength,the hardness decreases after the GBDP.The fracture mode of bended magnets changes from intergranular to transgranular.This study helps in further improving the mechanical and magnetic properties of sintered NdFeB magnets.
文摘In current research work,Dy3+substituted Mg0.5Cu0.25Co0.25Fe2-xDyxO4(0.0≤x≤0.04 with the step interval of 0.01)soft ferrites were synthesized by the sol-gel auto combustion method.The prepared samples were characterized by the techniques using X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),Fourier transform infrared(FTIR)spectroscopy,curre nt-voltage(Ⅰ-Ⅴ)measurement,LCR meter,vibrating sample magnetometer(VSM)and Raman.XRD data reveal that the average crystallite size is 49.71 nm and the lattice constant is 0.83703 nm for sample x=0.03.The non-uniform grain growth was demonstrated by micrographs and impurity-free elemental composition was observed from EDX analysis.The DC resistivity has an increasing and decreasing trend in ferromagnetic and paramagnetic regions with an increase in temperature.Moreover,the high resistivity is observed with the order of 1010Ω·cm,and the activation energy is 0.944 eV for samples x=0.03.The dielectric parameters including dielectric constant,dielectric losses,and impedance gradually decrease with the increase in frequency from 8 Hz to 8 MHz.The minimum dielectric loss at high frequency is found for sample x=0.03.The coercivity(Hc)and saturation magnetization(Ms)are found in the ranges of 520.82-544.02 Oe and 20.5841-21.1473 emu/g,respectively.These observations confirm that dysprosium(x=0.03)doped MCC-soft ferrites may be applicable in transformer cores,microwave absorbance,and telecommunication devices.
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 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.
