Micromagnetic study of magnetization reversal in inhomogeneous permanent magnets

Macroscopic magnetic properties of magnets strongly depend on the magnetization process and the microstructure of the magnets.Complex materials such as hard-soft exchange-coupled magnets or just real technical materials with impurities and inhomogeneities exhibit complex magnetization behavior.Here we investigate the effects of size,volume fraction,and surroundings of inhomogeneities on the magnetic properties of an inhomogeneous magnetic material via micromagnetic simulations.The underlying magnetization reversal and coercivity mechanisms are revealed.Three different demagnetization characteristics corresponding to the exchange coupling phase,semi-coupled phase,and decoupled phase are found,depending on the size of inhomogeneities.In addition,the increase in the size of inhomogeneities leads to a transition of the coercivity mechanism from nucleation to pinning.This work could be useful for optimizing the magnetic properties of both exchange-coupled nanomagnets and inhomogeneous single-phase magnets.

Federation Boosting Tree for Originator Rights Protection

The problem of data island hinders the application of big data in artificial intelligence model training,so researchers propose a federated learning framework.It enables model training without having to centralize all data in a central storage point.In the current horizontal federated learning scheme,each participant gets the final jointly trained model.No solution is proposed for scenarios where participants only provide training data in exchange for benefits,but do not care about the final jointly trained model.Therefore,this paper proposes a newboosted tree algorithm,calledRPBT(the originator Rights Protected federated Boosted Tree algorithm).Compared with the current horizontal federal learning algorithm,each participant will obtain the final jointly trained model.RPBT can guarantee that the local data of the participants will not be leaked,while the final jointly trained model cannot be obtained.It is worth mentioning that,from the perspective of the participants,the scheme uses the batch idea to make the participants participate in the training in random batches.Therefore,this scheme is more suitable for scenarios where a large number of participants are jointly modeling.Furthermore,a small number of participants will not actually participate in the joint training process.Therefore,the proposed scheme is more secure.Theoretical analysis and experimental evaluations show that RPBT is secure,accurate and efficient.

Tailored martensitic transformation and enhanced magnetocaloric effect in all-d-metal Ni_(35)Co_(15)Mn_(33)Fe_(2)Ti_(15)alloy ribbons

The crystal structure,martensitic transformation and magnetocaloric effect have been studied in all-d-metal Ni35Co15Mn33Fe2Ti15alloy ribbons with different wheel speeds(15 m/s(S15),30 m/s(S30),and 45 m/s(S45)).All three ribbons crystalize in B2-ordered structure at room temperature with crystal constants of 5.893(2)A,5.898(4)A,and5.898(6)A,respectively.With the increase of wheel speed,the martensitic transformation temperature decreases from230 K to 210 K,the Curie temperature increases slightly from 371 K to 378 K.At the same time,magnetic entropy change(△Sm)is also enhanced,as well as refrigeration capacity(RC).The maximum△Sm of 15.6(39.7)J/kg·K and RC of85.5(212.7)J/kg under?H=20(50)k Oe(1 Oe=79.5775 A·m^(-1))appear in S45.The results indicate that the ribbons could be the candidate for solid-state magnetic refrigeration materials.

The energy-free purification of trace thallium(I)-contaminated potable water using a high-selective filter paper with multi-layered Prussian blue decoration

Thallium is a highly toxic metal,and trace amount of thallium(I)(Tl+)in potable water could cause a severe water crisis,which arouses the exploitation of highly-effective technology for purification of Tl+contaminated water.This report proposes the multi-layered Prussian blue(PB)-decorated composite membranes(PBx@PDA/PEI-FP)based on the aminated filter papers for Tl+uptake.Extensively characterization by Fourier transform infrared spectrometer-attenuated total reflectance,scanning electron microscope,thermogravimetric analysis,X-ray photoelectron spectroscopy and X-ray diffraction were performed to confirm the in situ growth of cubic PB crystals on filter paper membrane surfaces via the aminated layers,and the successful fabrication of multi-layered PB overcoats via the increasing of aminated layers.The effect of PB layers on Tl+removal by PBx@PDA/PEI-FP from simulated drinking water was evaluated as well as the influence of different experimental conditions.A trade-off between PB decoration layer number and PB distribution sizes is existed in Tl+uptake by PBx@PDA/PEI-FP.The double-layered PB2@PDA/PEI-FP membrane showed the maximum sorption capacity,but its Tl+uptake performance was weakened by the acid,coexisting ions(K+and Na+)and powerful operation pressure,during filtrating a large volume of low-concentrated Tl+-containing water.However,the negative effect of coexisting ions on the Tl+uptake could be effectively eliminated in weak alkaline water,and the Tl+removal was increased up to 100%without any pressure driving for PB2@PDA/PEI-FP membrane.Most importantly,PB2@PDA/PEI-FP displayed the high-efficiency and high-selectivity in purifying the Tl+-spiked Pearl River water,in which the residual Tl+in filtrate was less than 2μg·L^(–1) to meet the drinking water standard of United States Environmental Protection Agency.This work provides a feasible avenue to safeguard the drinking water in remote and underdeveloped area via the energy-free operation.

The function of doping nitrogen on removing fluoride with decomposing La-MOF-NH_2:Density functional theory calculation and experiments

Fluoride is an important pollutant in wastewater,and adsorption is an effective way to remove fluoride.Because nitrogen plays an important role in adsorbent materials,computational models were developed to understand the changes in work function resulting from nitrogen doping.La-N-C-800℃,was prepared by pyrolyzing La-MOF-NH_(2)to verify the influence on the performance of removing fluoride by electrosorption.Material and electrochemical performance tests were performed to characterize La-N-C-800℃.Adsorption kinetics,adsorption thermodynamics,initial concentrations,pH,and ions competition were investigated using La-N-C-800℃for fluoride removal.In addition,density functional theory was applied to evaluate the function of nitrogen.When nitrogen atoms were added,the density of states,partial density of states,populations,and different orbits of charge were calculated to discover deep changes.Nitrogen strengthened the carbon structure and La_(2)O_(3)structure to remove fluoride.In addition,nitrogen can also act as an adsorption site in the carbon structure.These results provide design ideas for improving the performance of adsorbent materials by doping elements.

Microstructure evolution of hot-deformed SmCo-based nanocomposites induced by thermo-mechanical processing

Nanocomposite permanent magnets have ultra-high theoretical magnetic energy products,due to cou-pling of the soft/hard magnetic phases,inciting strict microstructural requirements.In this study,the microstructure evolution,including the phase transition,morphological changes,and texture formation,of hot-deformed SmCo-based nanocomposites under thermal-stress-strain coupling was characterized to determine a possible strategy for achieving high performance.The SmCo_(5)/α-Fe nanocomposites precursor contained fine and dispersed Sm(Fe,Co)_(5)and Fe-Co grains and exhibited a two-stage phase transforma-tion accompanied by grain growth.In the early stage of deformation at relatively low temperature,the adjacent Sm(Co,Fe)5 and Fe-Co phase formed the Sm_(2)(Co,Fe)_(17)-H phase,which was stable only with small grain sizes.In the high-temperature deformation stage,the Sm_(2)(Co,Fe)_(17)-H phase transformed into the Sm_(2)(Co,Fe)_(17)-R phase with large grain sizes.In addition,the strong c-axis texture formed in the Sm(Co,Fe)_(5)phase but not in the Sm_(2)(Co,Fe)_(17)-R phase.Subsequently,the phase transition process and texture formation mechanism were systematically analyzed by transmission electron microscopy.The ini-tiation of a slip system and/or preferential grain growth explained the formation of texture under the action of uniform stress and strain and assisted by dispersed Sm-rich nanograins.The Sm_(2)(Co,Fe)_(17)-R grains with poor orientations and large grain sizes did not achieve magnetic hardening,which also dam-age the magnetic properties.According to the results of this work,we also presented a new strategy to prepare high-performance SmCo-based nanocomposites magnets.

Combined Fenton process and sulfide precipitation for removal of heavy metals from industrial wastewater:Bench and pilot scale studies focusing on in-depth thallium removal

Thallium (Tl) in industrial wastewater is a public health concern due to its extremely high toxicity. However, there has been limited research regarding Tl removal techniques and engineering practices to date. In this investigation, bench and pilot studies on advanced treatment of industrial wastewater to remove Tl to a trace level were conducted. The treatment process involved a combination of hydroxide precipitation, Fenton oxidation, and sulfide precipitation. While hydroxide precipitation was ineffective for Tl^+ removal, it enabled the recovery of approximately 70%-80% of Zn as Zn hydroxide in alkaline conditions. The Fenton process provided good Tl removal (>95%) through oxidation and precipitation. Tl was then removed to trace levels (< 1.0 μg/L) via sulfide precipitation. Effective removal of other heavy metals was also achieved, with Cd < 13.4 μg/L, Cu < 39.6 μg/L, Pb < 5.32 μg/L, and Zn < 357 μg/L detected in the effluent. X-ray photoelectron spectroscopy indicated that T12S precipitate formed due to sulfide precipitation. Other heavy metals were removed via the formation of metal hydroxides during hydroxide precipitation and Fenton treatment, as well as via the formation of metal sulfides during sulfide precipitation. This combined process provides a scalable approach for the in-depth removal of Tl and other heavy metals from industrial wastewater.

Morphology and magnetic properties of Sm_(2)Co_(7)/α-Fe nanocomposite magnets produced by high energy ball milling and spark plasma sintering

In this article,the Sm_(2)Co_(7)/α-Fe nanocomposite magnets were prepared by high energy ball milling and spark plasma sintering method.The effect of soft phase content on the magnetic properties was studied.Up to 30 wt% α-Fe was added into Sm_(2)Co_(7) matrix without the decrease of remanence.Optimal energy product(BH)max of 9.2 MGOe was obtained with 20 wt% α-Fe.TEM observation shows that the grain size of α-Fe is 20-50 nm which ensures a good coupling effect between soft and hard phase.One more thing needs to be mentioned is that there exists inter-diffusion between Sm-Co phase and α-Fe phase.Moreover,our results can also illustrate that the Sm_(2)Co_(7)/α-Fe nanocomposite magnets are able to acquire better magnetic properties than the SmCo_(5)/α-Fe magnets prepared by the same process due to the large domain width of Sm_(2)Co_(7) phase.

Theory of high-density low-cross-talk waveguide superlattices

Waveguide superlattices, a special type of waveguide arrays, can be designed to achieve very low cross talk at submicrometer/subwavelength pitches. The theoretical framework and design rationales for such waveguide superlattices will be presented in depth. Waveguide sidewall roughness can help to deter the coherent coupling between identical waveguides in nearby supercells, but it also induces random fluctuation of transmission.Statistical behavior of the transmission due to roughness in a waveguide superlattice is systematically treated.Complex transmission characteristics due to spectral oscillation and random roughness will be presented, and their evolution with the superlattice length will be analyzed.

Analysis on deformation and texture formation mechanism of hot-deformed Nd-Fe-B magnets based on heterogeneous structure evolution

In this paper, microstructure, micromagnetic structure, texture, together with magnetic properties of the hot-deformed(HD) Nd-Fe-B magnets were systematically studied to understand the deformation process and the formation mechanism of c-axis texture. The results show that the platelet grains are formed in the fine-grain regions at the initial stage of the deformation. As the amount of deformation increases, the proportion of platelet grains increases and arranges gradually, causing the formation of c-axis texture, till the grain merging occurres when the deformation is excessive. It should be noted that the rare earth-rich phase in the fine-grained region slowly diffuses to the coarse-grained region where only grain growth can be observed during deformation. The deformation mechanism and formation of c-axis texture in HD Nd-Fe-B magnets can be deduced to be accomplished by the processes of dissolution-precipitation diffusion, grain rotation and grain arrangement, based on the characterization of microstructure and texture evolution. Also, approaches to optimize the preparation process and magnetic properties of the hot-deformed Nd-Fe-B magnets were discussed.

Preparation and characterization of sodium silicate/epoxy resin composite bonded Nd-Fe-B magnets with high performance

As an organic binder for bonded Nd-Fe-B magnets, epoxy resin(EP) has poor heat resistance but good moisture resistance, while sodium silicate(SS) has poor moisture absorption but better heat resistance and corrosion resistance. In order to improve high temperature stability and decrease moisture absorption of bonded Nd-Fe-B magnets, EP/SS composites were applied as the binder to prepare bonded Nd-Fe-B magnets. The magnetic properties, moisture absorption, corrosion resistance, compressive strength and microstructure of composite bonded magnets were investigated. The results show that EP/SS bonded magnets can obtain excellent magnetic properties at room temperature, and even useable magnetic properties a thigh temperature environments at 200°C. EP/SS composite binder effectively improves heat resistance and corrosion resistance of bonded Nd-Fe-B magnets, and reduces the hygroscopic properties. The molecule of sodium silicateis rigid and keeps it original shape at high temperature environments. In addition, SS in composite binder improves the mobility of the magnetic powders during the pre-pressing process, which makes the magnetic powders attain a more regular structure. These two factors will increase the mechanical properties. Moreover, sodium silicate in the composite binder can also cover the surfaces protecting the magnetic powders from oxidation and corrosion. EP in composite binder can cover SS surface to reduce the water absorption of SS as epoxy is a hydrophobic material. The EDX analysis shows that the composite binder has accumulated in the gaps of the magnet powders, which not only improves heat resistance and corrosion resistance, but also increases the mechanical properties. Therefore, EP/SS composite binder endows bonded Nd-Fe-B magnets excellent comprehensive properties.