查看更多>>摘要：The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported.The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring,the distribution of particles,and the particle size.The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect.An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data.This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.
查看更多>>摘要：Measuring the magneto-conductivity induced from impurities may help determine the impurity distribution and reveal the structure of a Weyl semimetal sample.To verify this,we utilize the Gaussian random disorder to simulate charged impurities in a two-node Weyl semimetal model and investigate the impact of charged impurities on magneto-conductivity in Weyl semimetals.We first compute the longitudinal magnetic conductivity and find that it is positive and increases proportionally with the parameter governing the Gaussian distribution of charged impurities,suggesting the presence of negative longitudinal magneto-resistivity.Then we consider both the intra-valley and inter-valley scattering processes to calculate the induced transverse magneto-conductivity in the model.Our findings indicate that both inter-valley and intra-valley scattering processes play important roles in the transverse magneto-conductivity.The locations of Weyl nodes can also be determined by magneto-conductivity measurements.This is possible if the magnetic field strength and the density of charged impurities are known.Alternatively,the measurement of magnetic conductivity may reveal the distribution of charged impurities in a given sample once the locations of the Weyl nodes have been determined.These findings can aid in detecting the structure of a Weyl semimetal sample,enhancing comprehension of magnetotransport in Weyl semimetals and promoting the development of valley electronics.
查看更多>>摘要：The Sm-Zr-Fe-Co-Ti quinary-alloys with ThMn12 structure has attracted wide attention for ultra-high intrinsic mag-netic properties,showing potentiality to be developed into rare-earth permanent magnets.The Ti element in alloys is crucial for phase stability and magnetic properties,and lower Ti content can increase intrinsic magnetic properties but reduce phase stability.In this study,the 1∶12 single-phase melt-spun ribbons with low Ti content was successfully prepared using a rapid solidification non-equilibrium method for the Sm1.1Zr0.2Fe9.2C02.3Tio.5 quinary-alloy.However,this non-equilibrium rib-bon did not achieve good magnetic hardening due to the uneven microstructure and microstrain.Then,annealing was carried out to eliminate micro-strain and homogenize microstructure,therefore,remanence and coercivity were significantly im-proved even the precipitation of a small amount of α-Fe phase which were not conducive to coercivity.The remanence of 86.1 emu/g and coercivity of 151 kA/m was achieved when annealing at 850 ℃ for 45 min.After hot pressing,under the action of high temperature and pressure,a small portion of ThMn12 phases in the magnet decompose into Sm-rich phases and α-Fe,while remanence of 4.02 kGs(1 Gs=10-4 T),and coercivity of 1.12 kOe(1 Oe=79.5775 A·m-1)were still acquired.Our findings can provide reference for exploring practical permanent magnets made of 1∶12 type quinary-alloys.
查看更多>>摘要：The unique cellular microstructure of Fe-rich Sm2Co17-type permanent magnets is closely associated with the struc-ture of the solid solution precursor.We investigate the phase structure,magnetic properties,and mechanical behavior of B-doped Sm2Co17-type magnets with high Fe content.The doped B atoms can diffuse into the interstitial vacancy,re-sulting in lattice expansion and promote the homogenization of the phase organizational structure during the solid solution treatment in theory.However,the resulting second phase plays a dominant role to result in more microtwin structures and highly ordered 2:17R phases in the solid solution stage,which inhibits the ordering transformation of 1:7H phase during aging and affects the generation of the cellular structure,and to result in a decrease in magnetic properties,yet the interface formed between it and the matrix phase hinders the movement of dislocations and enhances the mechanical properties.Hence,the precipitation of high flexural strain grain boundary phase induced by B element doping is also a new and effective way to improve the flexural strain of Sm2Co17-type magnets.Our study provides a new understanding of the phase structure evolution and its effect on the magnetic and mechanical properties of Sm2Co17-type magnets with high Fe content.
查看更多>>摘要：We described ferromagnetic film and bilayer films composed of two ferromagnetic layers coupled through antiferro-magnetic interfacial interaction by classical Heisenberg model and simulated their magnetization state,magnetic perme-ability,and Faraday effect at zero and finite temperature by using the Landau-Lifshitz-Gilbert(LLG)equation.The results indicate that in a microwave field with positive circular polarization,the ferromagnetic film has one resonance peak while the bilayer film has two resonance peaks.However,the resonance peak disappears in ferromagnetic film,and only one resonance peak emerges in bilayer film in the negative circularly polarized microwave field.When the microwave field's frequency exceeds the film's resonance frequency,the Faraday rotation angle of the ferromagnetic film is the greatest,and it decreases when the thickness of the two halves of the bilayer is reduced.When the microwave field's frequency remains constant,the Faraday rotation angle fluctuates with temperature in the same manner as spontaneous magnetization does.When a DC magnetic field is applied in the direction of the anisotropic axis of the film,the Faraday rotation angle varies with the DC magnetic field and shows a similar shape of the hysteresis loop.
查看更多>>摘要：The evolution process of magnetic domains in response to external fields is crucial for the modern understanding and application of spintronics.In this study,we investigated the domain rotation in stripe domain films of varying thicknesses by examining their response to microwave excitation in four different orientations.The resonance spectra indicate that the rotation field of stripe domain film under an applied magnetic field approaches the field where the resonance mode of sample changes.The saturation field of the stripe domain film corresponds to the field where the resonance mode disappears when measured in the stripe direction parallel to the microwave magnetic field.The results are reproducible and consistent with micromagnetic simulations,providing additional approaches and techniques for comprehending the microscopic mechanisms of magnetic domains and characterizing their rotation.
查看更多>>摘要：The dependences of spin wave resonance(SWR)frequency on the surface anisotropy field,interface exchange cou-pling,symmetry,biquadratic exchange(BQE)interaction,film thickness,and the external magnetic field in bilayer ferro-magnetic films are theoretically analyzed by employing the linear spin wave approximation and Green's function method.A remarkable increase of SWR frequency,except for energetically lower two modes,can be obtained in our model that takes the BQE interaction into account.Again,the effect of the external magnetic field on SWR frequency can be increased by increasing the biquadratic to interlayer exchange ratio.It has been identified that the BQE interaction is of utmost impor-tance in improving the SWR frequency of the bilayer ferromagnetic films.In addition,for bilayer ferromagnetic films,the frequency gap between the energetically highest mode and lowest mode is found to increase by increasing the biquadratic to interlayer exchange ratio and film thickness and destroying the symmetry of the system.These results can be used to improve the understanding of magnetic properties in bilayer ferromagnetic films and thus may have prominent implications for future magnetic devices.
查看更多>>摘要：This study investigated the effect of antioxidants on the grinding efficiency,magnetic powder characteristics,mi-crostructure,and magnetic properties of 2∶17 type SmCo permanent magnet materials.The results show that adding an-tioxidants helps improve the dispersion among magnetic powders,leading to a 33.3％decrease in jet milling time and a 15.8％increase in magnet powder production yield.Additionally,adding antioxidants enhances the oxidation resistance of the magnetic powders.After being stored in a constant temperature air environment at 25 ℃ for 48 h,the O content in the powder decreased by 33％compared to samples without antioxidants.While in the magnet body,the O content decreased from 0.21 wt.％to 0.14 wt.％,which helps increase the effective Sm content and domain wall pinning uniformity in the magnet.Excellent magnetic properties were obtained in the magnet with added antioxidants:Br=11.6 kGs,SF=79.6％,Hcj=16.8 kOe,and(BH)max=32.5 MGOe.
查看更多>>摘要：Deformation can change the transition pathway of materials under high pressure,thus significantly affects physical and chemical properties of matters.However,accurate pressure calibration under deformation is challenging and thereby causes relatively large pressure uncertainties in deformation experiments,resulting in the synthesis of complex multiphase materials.Here,pressure generations of three types of deformation assemblies were well calibrated in a Walker-type large-volume press(LVP)by electrical resistance measurements combined with finite element simulations(FESs).Hard Al203 or diamond pistons in shear and uniaxial deformation assemblies significantly increase the efficiency of pressure generation compared with the conventional quasi-hydrostatic assembly.The uniaxial deformation assembly using flat diamond pistons possesses the highest efficiency in these deformation assemblies.This finding is further confirmed by stress distribution analysis based on FESs.With this deformation assembly,we found shear can effectively promote the transformation of C60 into diamond under high pressure and realized the synthesis of phase-pure diamond at relatively moderate pressure and temperature conditions.The present developed techniques will help improve pressure efficiencies in LVP and explore the new physical and chemical properties of materials under deformation in both science and technology.
查看更多>>摘要：Ultraviolet photodetectors(UV PDs)are widely used in civilian,scientific,and military fields due to their high sensi-tivity and low false alarm rates.We present a temperature-dependent Lewis acid p-type doping method for transition metal dichalcogenides(TMDs),which can effectively be used to extend the optical response range.The p-type doping based on surface charge transfer involves the chemical adsorption of the Lewis acid SnCl4 as a light absorption layer on the surface of WS2,significantly enhancing its UV photodetection performance.Under 365 nm laser irradiation,WS2 PDs exhibit response speed of 24 ms/20 ms,responsivity of 660 mA/W,detectivity of 3.3 × 1011 Jones,and external quantum efficiency of 226％.Moreover,we successfully apply this doping method to other TMDs materials(such as MoS2,MoSe2,and WSe2)and fabricate WS2 lateral p-n heterojunction PDs.
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