Microwave permeability spectra of single Co nanotube under equilibrium state have been studied by micromagnetics simulation.More than four obvious resonance peaks have been found(11.72,24.20,33.18 and 39.55 GHz).Such ...Microwave permeability spectra of single Co nanotube under equilibrium state have been studied by micromagnetics simulation.More than four obvious resonance peaks have been found(11.72,24.20,33.18 and 39.55 GHz).Such large resonance frequency cannot be found in other traditional magnetic materials.The configurations of magnetic moments along the nanotube have been simulated.The results show that the top end of nanotube has a"flow-out"pattern of magnetic moments configuration.The bottom end has a"flow-in"pattern of magnetic moments configuration.The magnetic moments within the main body of nanotube are aligned perfectly along the length of nanotube.The magnitude of natural resonance peak is strongly related to the volume fraction of a zone,which has the same orientation of magnetic moments.Large microwave permeability values have been found for single nanotube.The generalized Snoek’s law has been used to validate the micromagnetics simulations in this paper.展开更多
Magnetoelastic couplings in giant magnetostrictive materials(GMMs)attract significant interests due to their extensive applications in the fields of spintronics and energy harvesting devices.Understanding the role of ...Magnetoelastic couplings in giant magnetostrictive materials(GMMs)attract significant interests due to their extensive applications in the fields of spintronics and energy harvesting devices.Understanding the role of the selection of materials and the response to external fields is essential for attaining desired functionality of a GMM.Herein,machine learning(ML)models are conducted to predict saturation magnetostrictions(λ_(s))in RFe_(2)-type(R=rare earth)GMMs with different compositions.According to ML-predicted composition–λsrelations,it is discovered that the values ofλshigher than1100×10^(-6)are almost situated in the composition space surrounded by 0.26≤x≤0.60 and 1.90≤y≤2.00 for the ternary compounds of Tb_(x)Dy_(1-x)Fe_(y).Assisted by ML predictions,the compositions are further narrowed down to the space surrounded by 0.26≤x≤0.32 and 1.92≤y≤1.97 for the excellent piezomagnetic(PM)performance in the Tb_(x)Dy_(1-x)Fe_(y)based PM device through our developed high-throughput(HTP)micromagnetic simulation(MMS)algorithm.Accordingly,high sensitivities up to10.22-13.61 m T·MPa^(-1)are observed in the optimized range within which the available experimental data fall well.This work not only provides valuable insights toward understanding the mechanism of magnetoelastic couplings,but also paves the way for designing and optimizing highperformance magnetostrictive materials and PM sensing devices.展开更多
MicroMagnetic.jl is an open-source Julia package for micromagnetic and atomistic simulations.Using the features of the Julia programming language,MicroMagnetic.jl supports CPU and various GPU platforms,including NVIDI...MicroMagnetic.jl is an open-source Julia package for micromagnetic and atomistic simulations.Using the features of the Julia programming language,MicroMagnetic.jl supports CPU and various GPU platforms,including NVIDIA,AMD,Intel,and Apple GPUs.Moreover,MicroMagnetic.jl supports Monte Carlo simulations for atomistic models and implements the nudged-elastic-band method for energy barrier computations.With built-in support for double and single precision modes and a design allowing easy extensibility to add new features,MicroMagnetic.jl provides a versatile toolset for researchers in micromagnetics and atomistic simulations.展开更多
The competition between dimensionality and ordering in multiferroic materials is of great interest for both fundamental physics and potential applications. Combining first-principles calculations with micromagnetic si...The competition between dimensionality and ordering in multiferroic materials is of great interest for both fundamental physics and potential applications. Combining first-principles calculations with micromagnetic simulations, we investigate recently synthesized ultrathin perovskite bismuth ferrite(BFO) films. Our numerical results reveal that, at the monolayer limit, the ferroelectricity of BFO is missing because the octahedral distortions are constrained. However, the monolayer bismuth ferrite is a topological antiferromagnetic metal with tunable bimeron magnetic structure. The dual topologically non-trivial characteristics make monolayer bismuth ferrite a multifunctional building block in future spintronic devices.展开更多
We proposed a new measure to optimize the comprehensive magnetic properties of SmCo_(5)alloy.By compounding Fe-15Ni-3Al-1Ti(FNAT)alloy with high saturation magnetization and Sm(Co,Cu)_(5) matrix alloy in the liquid st...We proposed a new measure to optimize the comprehensive magnetic properties of SmCo_(5)alloy.By compounding Fe-15Ni-3Al-1Ti(FNAT)alloy with high saturation magnetization and Sm(Co,Cu)_(5) matrix alloy in the liquid state,an innovative two-phase separation microstructure or cellular microstructure is formed after melt-spinning using the phase separation effect of the two alloys.At the same time,the element concentration,relative phase content,and microstructure are adjusted by adding different contents of FNAT alloy.The results show that FNAT addition promotes the as-spun ribbons phase separation(or spinodal decomposition)into Co-rich SmCo_(5)-and Sm-Ni-rich CeCo_(5)-or Sm_(2)Co_(7)-type phases.Adding 3 wt.%FNAT increases the coercivity,saturation magnetization,and remanence of the ribbons by 320.6%,39.8%,and 82.8%,respectively.Adding 5 wt.%FNAT promotes forming the Sm_(2)(Co,M)_(7) cell-wall phase and increases the coercivity and remanence by 272.7%and 48.1%,respectively.Finally,the corresponding microstructure evolution models,magnetization,and demagnetization mechanisms are proposed.展开更多
In this study,DyF_(3)powder was sprayed onto the polar and side surfaces of the magnets to determine the anisotropic diffusion mechanism of Dy in the sintered Nd-Fe-B magnet.The coercivity and squareness of the magnet...In this study,DyF_(3)powder was sprayed onto the polar and side surfaces of the magnets to determine the anisotropic diffusion mechanism of Dy in the sintered Nd-Fe-B magnet.The coercivity and squareness of the magnet in which the diffusion of Dy is perpendicular to the c-axis(a-magnet)are lower than those of the magnet with the diffusion of Dy parallel to the c-axis(c-magnet).Compared with the c-magnet,the a-magnet has a longer Dy-enrichment region from the diffusion surface,where Dy is enriched in the 2:14:1 grain.By contrast,the Dy concentration in the grain boundaries beyond the Dy enrichment region is lower in the a-magnet.Moreover,the Dy shells beyond the Dy enrichment region in the a-magnet are distributed on the side surfaces of the 2:14:1 grains but not on the polar surfaces.Based on the micromagnetic simulation,the Dy shells on the polar surfaces of the grains are more effective in enhancing coercivity.According to first-principle calculations,Dy migrating through 001 into the Nd vacancy in the Nd_(2)Fe_(14)B crystal has a higher diffusion barrier,thus indicating that the lattice diffusion of Dy parallel to the c-axis is more difficult.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
A sintered Nd-Y-Fe-B magnet was designed and manufactured by the multi-main-phase process.Unevenly distributed Y in the magnet decreases the adverse magnetic weakening effect of Y on the coercivity.Grain boundary diff...A sintered Nd-Y-Fe-B magnet was designed and manufactured by the multi-main-phase process.Unevenly distributed Y in the magnet decreases the adverse magnetic weakening effect of Y on the coercivity.Grain boundary diffusion process(GBDP)was conducted to further enhance the coercivity of the Nd-Y-Fe-B magnet.The coercivity increases significantly from 884 to 1741 kA/m after GBDP with Pr_(60)Tb_(10)Cu_(30)alloy.The mechanism of the coercivity enhancement is discussed based on the microstructure analysis.Micromagnetic simulation reveals that when the diffused Tb-rich shell thickness is lower than 12 nm the c-plane shell(perpendicular to the c-axis)is much more effective in enhancing the coercivity than the side plane shell(parallel to the c-axis).But when the Tb-rich shell thickness is above12 nm the side plane shell contributes more to the coercivity enhancement.The results in this work can help to design and manufacture Nd-Fe-B magnets with low cost and high magnetic properties.展开更多
Bit patterned recording(BPR)has attracted much attention due to its promising potential in achieving high densities in magnetic storage devices.The materials with strong perpendicular magnetic anisotropy(PMA)are alway...Bit patterned recording(BPR)has attracted much attention due to its promising potential in achieving high densities in magnetic storage devices.The materials with strong perpendicular magnetic anisotropy(PMA)are always preferred in designing the BPR.Here,the patterned Co/Ni multilayers showing d-d hybridization induced PMA was studied.In particular,we record the ultrafast spin dynamics by means of time-resolved scanning magneto-optical Kerr effect(TRMOKE)microscopy.We are able to acquire the“snapshot”magnetic maps of the sample surface because of both the femtosecond temporal and submicrometer spatial resolution in our TRMOKE microscopy.Furthermore,the spatially inhomogeneous ultrafast demagnetization was observed in experiment,and this has been evidenced by simulations.展开更多
Hysteresis loops and energy products have been calculated systematically by a three-dimensional （3D） software OOMMF for Sm-Co/α-Fe/Sm-Co trilayers with various thicknesses and β, where β is the angle between the ...Hysteresis loops and energy products have been calculated systematically by a three-dimensional （3D） software OOMMF for Sm-Co/α-Fe/Sm-Co trilayers with various thicknesses and β, where β is the angle between the easy axis and the field applied perpendicular to the film plane. It is found that trilayers with a perpendicular anisotropy possess considerably larger coercivities and smaller remanences and energy products compared with those with an in-plane anisotropy. Increase of β leads to a fast decrease of the maximum energy product as well as the drop of both remanence and coercivity. Such a drop is much faster than that in the single-phased hard material, which can explain the significant discrepancy between the experiment and the theoretical energy products. Some modeling techniques have been utilized with spin check procedures performed, which yield results in good agreement with the one-dimensional （1D） analytical and experimental data, justifying our calculations. Further, the calculated nucleation fields according to the 3D calculations are larger than those based on the 1D model, whereas the corresponding coercivity is smaller, leading to more square hysteresis loops and better agreement between experimental data and the theory.展开更多
Micromagnetic simulations have been performed to obtain the dynamic susceptibility spectra of 4×4 cobalt nanowire arrays with different spatial configurations and geometries. The susceptibility spectra of isolate...Micromagnetic simulations have been performed to obtain the dynamic susceptibility spectra of 4×4 cobalt nanowire arrays with different spatial configurations and geometries. The susceptibility spectra of isolated wires have also been simulated for comparison purposes. It is found that the susceptibility spectrum of nanowire array bears a lot of similarities to that of an isolated wire, such as the occurrences of the edge mode and the bulk resonance mode. The simulation results also reveal that the susceptibility spectrum of nanowire array behaves like that of single isolated wire as the interwire distance grows to an extent, which is believed due to the decrease of magnetostatic interaction among nanowires, and can be further confirmed by the static magnetic hysteresis simulations. In comparison with single nanowire, magnetostatic interaction may increase or decrease the resonance frequencies of nanowire arrays assuming a certain interwire distance when the length of array increases. Our simulation results are also analysed by employing the Kittel equation and recent theoretical studies.展开更多
The soft/hard composite patterned media have potential to be the next generation of magnetic recording, but the composing modes of soft and hard materials have not been investigated systematically. L10 FePt-based soft...The soft/hard composite patterned media have potential to be the next generation of magnetic recording, but the composing modes of soft and hard materials have not been investigated systematically. L10 FePt-based soft/hard composite patterned media with an anisotropic constant distribution are studied by micromagnetic simulation. Square arrays and hexagonal arrays with various pitch sizes are simulated for two composing types： the soft layer that encloses the hard dots and the soft layer that covers the whole surface. It is found that the soft material can reduce the switching fields of bits effectively for all models. Compared with the first type, the second type of models possess low switching fields, narrow switching field distributions, and high gain factors due to the introduction of inter-bit exchange coupling. Furthermore, the readout waveforms of the second type are not deteriorated by the inter-bit soft layers. Since the recording density of hexagonal arrays are higher than that of square arrays with the same center-to-center distances, the readout waveforrns of hexagonal arrays are a little worse, although other simulation results are similar for these two arrays.展开更多
In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L10-FePt which is magnetized perpendicularly to film plane and the sense layer is NiFe which is magnetized in t...In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L10-FePt which is magnetized perpendicularly to film plane and the sense layer is NiFe which is magnetized in the film plane. The magnetization configurations of the hard and sense layers at different external magnetic fields have been simulated. In micromagnetic simulation, the sense field up to one tesla can be reached by using this sensor. We find that whether the sensor has a symmetric or an asymmetric field-sensing window is determined by the coercive field of the hard layer and the demagnetizing field of the sense layer.展开更多
The single-pole tip (SPT) heads made of the high saturation FeCo ferromagnetic metals are crucial for the actualization of ultrahigh density perpendicular recording. The effective head field distribution in the medium...The single-pole tip (SPT) heads made of the high saturation FeCo ferromagnetic metals are crucial for the actualization of ultrahigh density perpendicular recording. The effective head field distribution in the medium is of key importance for the design of the SPT head, which would be analyzed by micromagnetic simulations in this work. Two 3D micromagnetic models of the SPT head were established to select a more appropriate method of modeling, with a magnetostatic image effect or a real soft magnetic material to model the image of the SPT head in soft under layer (SUL). The results from these two designs were tested and compared to the ideal head field calculated by the Jacobi finite element method (FEM); and the design with the real soft magnetic material as image was proved suitable for simulating the ultrahigh density perpendicular recording write head.展开更多
Owing to the epitaxial inducement of Au atom,Au interlayer was introduced to increase the perpendicular anisotropy and the coercivity in L10-FePt nanocomposite film.Micromagnetics can be used to reveal the relationshi...Owing to the epitaxial inducement of Au atom,Au interlayer was introduced to increase the perpendicular anisotropy and the coercivity in L10-FePt nanocomposite film.Micromagnetics can be used to reveal the relationship between microstructure and magnetic properties of materials,and give the information of the perpendicular anisotropy and coercivity.In this work,the effect of the Au interlayer on annealed[Fe（0.5 nm）/Pt（0.5 nm）/Au（d nm）]10 nanocomposite recording medium by a micromagnetic model was studied.The model contains three phases：hard magnetic phase,soft magnetic phase,and nonmagnetic phase.The calculated result shows that perpendicular orientation degree of the texture and proportion of a hard magnetic phase to the total phase in the annealed film are both enhanced by increasing Au interlayer thickness.This result can be conducive to the improvement of the perpendicular anisotropy and the coercivity of the FePt nanocomposite film in the experiments.展开更多
The effects of the number and the location of notches on the formation of flux-closure states in bi-rings with fields applied in the x direction （i.e., along the short axis direction of hi-rings） and y direction （i...The effects of the number and the location of notches on the formation of flux-closure states in bi-rings with fields applied in the x direction （i.e., along the short axis direction of hi-rings） and y direction （i.e., along the long axis direction of bi-rings） are investigated using micromagnetic simulation. For the bi-rings with one notch and the bi-rings with two notches symmetric about y axis, the order of flux-closure state formation in each ring can be controlled. But the flux-closure state forms simultaneously in each ring for the bi-rings with two notches symmetric about x axis. For the bi-rings with two notches that are symmetric neither about x axis nor about y axis, only one ring can form a flux- closure state in the y-direction field and no fluxclosure state can be found in rings in the x-direction field. Therefore, logic states can be defined by controlling the order of flux-closure state formation, which can be utilized in future logic devices.展开更多
In this study, micromagnetism simulation by using timte dltterence method is cameo out on the Ncl21-el415/a-Fe nanocomposite magnet with soft phase imbedded in hard phase. The effects of soft magnetic phase size （S）...In this study, micromagnetism simulation by using timte dltterence method is cameo out on the Ncl21-el415/a-Fe nanocomposite magnet with soft phase imbedded in hard phase. The effects of soft magnetic phase size （S） on the magnetic properties and magnetic reversal modes are systematically analyzed. As S increases from 1 nm to 48 nm, the remanence （Jr） increases, while the coercivity （Hci） decreases, leading to the result that the magnetic energy prod- uct [（BH）max] first increases slowly, and then decreases rapidly, peaking at S = 24 nm with the （BH）max of 72.9 MGOe （1 MGOe = 7.95775 kJ.m-3）. Besides, with the increase of S, the coercivity mechanism of the nanocomposite magnet changes from nucleation to pinning. Furthermore, by observing the magnetic moment evolution in demagnetization pro- cess, the magnetic reversal of the soft phase in the nanocomposite magnet can be divided into three modes with the increase of S： coherent rotation （S 〈 3 nm）, quasi-coherent rotation （3 nm≤S 〈 36 nm）, and the vortex-like rotation （S ≥36 nm）.展开更多
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 ...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.展开更多
Skyrmions, with their vortex-like structures and inherent topological protection, play a pivotal role in developing innovative low-power memory and logic devices. The efficient generation and control of skyrmions in g...Skyrmions, with their vortex-like structures and inherent topological protection, play a pivotal role in developing innovative low-power memory and logic devices. The efficient generation and control of skyrmions in geometrically confined systems are crucial for the development of skyrmion-based spintronic devices. In this study, we focus on investigating the non-reciprocal transport behavior of skyrmions and their interactions with boundaries of various shapes. The shape of the notch structure in the nanotrack significantly affects the dynamic behavior of magnetic skyrmions. Through micromagnetic simulation, the non-reciprocal transport properties of skyrmions in nanowires with different notch structures are investigated in this work.展开更多
Recent theory and experiments show that artificial magnetic skyrmions can be stabilized at room temperature without the need for the external magnetic field,casting strong potentials for the device applications.In thi...Recent theory and experiments show that artificial magnetic skyrmions can be stabilized at room temperature without the need for the external magnetic field,casting strong potentials for the device applications.In this work,we study the electric field manipulation of artificial magnetic skyrmions imprinted by Co disks on CoPt multilayers utilizing the micromagnetic simulations.We find that the reversible annihilation and creation of skyrmions can be realized with the electric field via the strain mediated magnetoelastic coupling.In addition,we also demonstrate controllable manipulation of individual skyrmion,which opens a new platform for constructing magnetic field-free and low-energy dissipation skyrmion based media.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.61271039)the Scientific Foundation of Young Scientists of Sichuan Province(Grant No.2012JQ0053)the Program for New Century Excellent Talents in Universities(NCET-11-0060)
文摘Microwave permeability spectra of single Co nanotube under equilibrium state have been studied by micromagnetics simulation.More than four obvious resonance peaks have been found(11.72,24.20,33.18 and 39.55 GHz).Such large resonance frequency cannot be found in other traditional magnetic materials.The configurations of magnetic moments along the nanotube have been simulated.The results show that the top end of nanotube has a"flow-out"pattern of magnetic moments configuration.The bottom end has a"flow-in"pattern of magnetic moments configuration.The magnetic moments within the main body of nanotube are aligned perfectly along the length of nanotube.The magnitude of natural resonance peak is strongly related to the volume fraction of a zone,which has the same orientation of magnetic moments.Large microwave permeability values have been found for single nanotube.The generalized Snoek’s law has been used to validate the micromagnetics simulations in this paper.
基金financially supported by the National Key R&D Program of China(No.2021YFB3501401)the National Natural Science Foundation of China(Nos.52001103,U22A20117)Zhejiang Provincial Natural Science Foundation of China(No.LQ21E010001)。
文摘Magnetoelastic couplings in giant magnetostrictive materials(GMMs)attract significant interests due to their extensive applications in the fields of spintronics and energy harvesting devices.Understanding the role of the selection of materials and the response to external fields is essential for attaining desired functionality of a GMM.Herein,machine learning(ML)models are conducted to predict saturation magnetostrictions(λ_(s))in RFe_(2)-type(R=rare earth)GMMs with different compositions.According to ML-predicted composition–λsrelations,it is discovered that the values ofλshigher than1100×10^(-6)are almost situated in the composition space surrounded by 0.26≤x≤0.60 and 1.90≤y≤2.00 for the ternary compounds of Tb_(x)Dy_(1-x)Fe_(y).Assisted by ML predictions,the compositions are further narrowed down to the space surrounded by 0.26≤x≤0.32 and 1.92≤y≤1.97 for the excellent piezomagnetic(PM)performance in the Tb_(x)Dy_(1-x)Fe_(y)based PM device through our developed high-throughput(HTP)micromagnetic simulation(MMS)algorithm.Accordingly,high sensitivities up to10.22-13.61 m T·MPa^(-1)are observed in the optimized range within which the available experimental data fall well.This work not only provides valuable insights toward understanding the mechanism of magnetoelastic couplings,but also paves the way for designing and optimizing highperformance magnetostrictive materials and PM sensing devices.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1403603)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB33030100)+2 种基金the National Natural Science Fund for Distinguished Young Scholar(Grant No.52325105)the National Natural Science Foundation of China(Grant Nos.12374098,11974021,and 12241406)the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-084).
文摘MicroMagnetic.jl is an open-source Julia package for micromagnetic and atomistic simulations.Using the features of the Julia programming language,MicroMagnetic.jl supports CPU and various GPU platforms,including NVIDIA,AMD,Intel,and Apple GPUs.Moreover,MicroMagnetic.jl supports Monte Carlo simulations for atomistic models and implements the nudged-elastic-band method for energy barrier computations.With built-in support for double and single precision modes and a design allowing easy extensibility to add new features,MicroMagnetic.jl provides a versatile toolset for researchers in micromagnetics and atomistic simulations.
基金supported by the National Natural Science Foundation of China (Grant No. 12174382)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDB0460000 and XDB28000000)the Innovation Program for Quantum Science and Technology (Grant Nos. 2024ZD0300104 and 2021ZD0302600)。
文摘The competition between dimensionality and ordering in multiferroic materials is of great interest for both fundamental physics and potential applications. Combining first-principles calculations with micromagnetic simulations, we investigate recently synthesized ultrathin perovskite bismuth ferrite(BFO) films. Our numerical results reveal that, at the monolayer limit, the ferroelectricity of BFO is missing because the octahedral distortions are constrained. However, the monolayer bismuth ferrite is a topological antiferromagnetic metal with tunable bimeron magnetic structure. The dual topologically non-trivial characteristics make monolayer bismuth ferrite a multifunctional building block in future spintronic devices.
基金supported by the General Program from the National Natural Science Foundation of China(NNSFC)(No.52371185)Central Government Guides Local Funds for Science and Technology Development(No.216Z1008G)the Natural Science Foundation of Hebei province,China(No.E2022202017).
文摘We proposed a new measure to optimize the comprehensive magnetic properties of SmCo_(5)alloy.By compounding Fe-15Ni-3Al-1Ti(FNAT)alloy with high saturation magnetization and Sm(Co,Cu)_(5) matrix alloy in the liquid state,an innovative two-phase separation microstructure or cellular microstructure is formed after melt-spinning using the phase separation effect of the two alloys.At the same time,the element concentration,relative phase content,and microstructure are adjusted by adding different contents of FNAT alloy.The results show that FNAT addition promotes the as-spun ribbons phase separation(or spinodal decomposition)into Co-rich SmCo_(5)-and Sm-Ni-rich CeCo_(5)-or Sm_(2)Co_(7)-type phases.Adding 3 wt.%FNAT increases the coercivity,saturation magnetization,and remanence of the ribbons by 320.6%,39.8%,and 82.8%,respectively.Adding 5 wt.%FNAT promotes forming the Sm_(2)(Co,M)_(7) cell-wall phase and increases the coercivity and remanence by 272.7%and 48.1%,respectively.Finally,the corresponding microstructure evolution models,magnetization,and demagnetization mechanisms are proposed.
基金supported by the National Natural Science Foundation of China(52361033)National Key Research and Development Program(2022YFB3505400)+1 种基金the Main Discipline and Technology Leaders Training Plan of Jiangxi Province(2022BCJ23007)the Jiangxi Province Postgraduate Innovation Project(YC2022-S693)。
文摘In this study,DyF_(3)powder was sprayed onto the polar and side surfaces of the magnets to determine the anisotropic diffusion mechanism of Dy in the sintered Nd-Fe-B magnet.The coercivity and squareness of the magnet in which the diffusion of Dy is perpendicular to the c-axis(a-magnet)are lower than those of the magnet with the diffusion of Dy parallel to the c-axis(c-magnet).Compared with the c-magnet,the a-magnet has a longer Dy-enrichment region from the diffusion surface,where Dy is enriched in the 2:14:1 grain.By contrast,the Dy concentration in the grain boundaries beyond the Dy enrichment region is lower in the a-magnet.Moreover,the Dy shells beyond the Dy enrichment region in the a-magnet are distributed on the side surfaces of the 2:14:1 grains but not on the polar surfaces.Based on the micromagnetic simulation,the Dy shells on the polar surfaces of the grains are more effective in enhancing coercivity.According to first-principle calculations,Dy migrating through 001 into the Nd vacancy in the Nd_(2)Fe_(14)B crystal has a higher diffusion barrier,thus indicating that the lattice diffusion of Dy parallel to the c-axis is more difficult.
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 the National Natural Science Foundation of China(51901087)China Postdoctoral Science Foundation(2021M701504)。
文摘A sintered Nd-Y-Fe-B magnet was designed and manufactured by the multi-main-phase process.Unevenly distributed Y in the magnet decreases the adverse magnetic weakening effect of Y on the coercivity.Grain boundary diffusion process(GBDP)was conducted to further enhance the coercivity of the Nd-Y-Fe-B magnet.The coercivity increases significantly from 884 to 1741 kA/m after GBDP with Pr_(60)Tb_(10)Cu_(30)alloy.The mechanism of the coercivity enhancement is discussed based on the microstructure analysis.Micromagnetic simulation reveals that when the diffused Tb-rich shell thickness is lower than 12 nm the c-plane shell(perpendicular to the c-axis)is much more effective in enhancing the coercivity than the side plane shell(parallel to the c-axis).But when the Tb-rich shell thickness is above12 nm the side plane shell contributes more to the coercivity enhancement.The results in this work can help to design and manufacture Nd-Fe-B magnets with low cost and high magnetic properties.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFA1403302)the National Natural Science Foundation of China(Grant Nos.52031015,U22A20115,and 12104030)+1 种基金the Natural Science Foundation of Zhejiang Province,China(Grant No.LZ25A040007)the Natural Science Foundation of Beijing(Grant No.1252026).
文摘Bit patterned recording(BPR)has attracted much attention due to its promising potential in achieving high densities in magnetic storage devices.The materials with strong perpendicular magnetic anisotropy(PMA)are always preferred in designing the BPR.Here,the patterned Co/Ni multilayers showing d-d hybridization induced PMA was studied.In particular,we record the ultrafast spin dynamics by means of time-resolved scanning magneto-optical Kerr effect(TRMOKE)microscopy.We are able to acquire the“snapshot”magnetic maps of the sample surface because of both the femtosecond temporal and submicrometer spatial resolution in our TRMOKE microscopy.Furthermore,the spatially inhomogeneous ultrafast demagnetization was observed in experiment,and this has been evidenced by simulations.
基金supported by the National Natural Science Foundation of China(Grant Nos.11074179,10747007,51331003,51371011,and 51001002)the State Key Development Program of Basic Research of China(Grant No.2010CB934600)+2 种基金the Construction Plan for Scientific Research Innovation Teams of Universities in Sichuan Province,China(Grant No.12TD008)the Beijing Municipal Natural Science Foundation,China(Grant No.2122006)Scientific Research Innovation Fund for Student in Sichuan Normal University,China
文摘Hysteresis loops and energy products have been calculated systematically by a three-dimensional （3D） software OOMMF for Sm-Co/α-Fe/Sm-Co trilayers with various thicknesses and β, where β is the angle between the easy axis and the field applied perpendicular to the film plane. It is found that trilayers with a perpendicular anisotropy possess considerably larger coercivities and smaller remanences and energy products compared with those with an in-plane anisotropy. Increase of β leads to a fast decrease of the maximum energy product as well as the drop of both remanence and coercivity. Such a drop is much faster than that in the single-phased hard material, which can explain the significant discrepancy between the experiment and the theoretical energy products. Some modeling techniques have been utilized with spin check procedures performed, which yield results in good agreement with the one-dimensional （1D） analytical and experimental data, justifying our calculations. Further, the calculated nucleation fields according to the 3D calculations are larger than those based on the 1D model, whereas the corresponding coercivity is smaller, leading to more square hysteresis loops and better agreement between experimental data and the theory.
基金Project supported by the National Natural Science Foundation of China(Grant No.60701016)the National Natural Science Foundation of China-the Royal Society of United Kingdom International Jointed Project(Grant No.60911130130)
文摘Micromagnetic simulations have been performed to obtain the dynamic susceptibility spectra of 4×4 cobalt nanowire arrays with different spatial configurations and geometries. The susceptibility spectra of isolated wires have also been simulated for comparison purposes. It is found that the susceptibility spectrum of nanowire array bears a lot of similarities to that of an isolated wire, such as the occurrences of the edge mode and the bulk resonance mode. The simulation results also reveal that the susceptibility spectrum of nanowire array behaves like that of single isolated wire as the interwire distance grows to an extent, which is believed due to the decrease of magnetostatic interaction among nanowires, and can be further confirmed by the static magnetic hysteresis simulations. In comparison with single nanowire, magnetostatic interaction may increase or decrease the resonance frequencies of nanowire arrays assuming a certain interwire distance when the length of array increases. Our simulation results are also analysed by employing the Kittel equation and recent theoretical studies.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51171086 and 61272076)the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.61003041)
文摘The soft/hard composite patterned media have potential to be the next generation of magnetic recording, but the composing modes of soft and hard materials have not been investigated systematically. L10 FePt-based soft/hard composite patterned media with an anisotropic constant distribution are studied by micromagnetic simulation. Square arrays and hexagonal arrays with various pitch sizes are simulated for two composing types： the soft layer that encloses the hard dots and the soft layer that covers the whole surface. It is found that the soft material can reduce the switching fields of bits effectively for all models. Compared with the first type, the second type of models possess low switching fields, narrow switching field distributions, and high gain factors due to the introduction of inter-bit exchange coupling. Furthermore, the readout waveforms of the second type are not deteriorated by the inter-bit soft layers. Since the recording density of hexagonal arrays are higher than that of square arrays with the same center-to-center distances, the readout waveforrns of hexagonal arrays are a little worse, although other simulation results are similar for these two arrays.
基金Project supported by the Nature Science Foundation of China （Grant No 10404019） and by the Science and Technology Committee of Shanghai （Grant No 05PJ14090）.
文摘In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L10-FePt which is magnetized perpendicularly to film plane and the sense layer is NiFe which is magnetized in the film plane. The magnetization configurations of the hard and sense layers at different external magnetic fields have been simulated. In micromagnetic simulation, the sense field up to one tesla can be reached by using this sensor. We find that whether the sensor has a symmetric or an asymmetric field-sensing window is determined by the coercive field of the hard layer and the demagnetizing field of the sense layer.
文摘The single-pole tip (SPT) heads made of the high saturation FeCo ferromagnetic metals are crucial for the actualization of ultrahigh density perpendicular recording. The effective head field distribution in the medium is of key importance for the design of the SPT head, which would be analyzed by micromagnetic simulations in this work. Two 3D micromagnetic models of the SPT head were established to select a more appropriate method of modeling, with a magnetostatic image effect or a real soft magnetic material to model the image of the SPT head in soft under layer (SUL). The results from these two designs were tested and compared to the ideal head field calculated by the Jacobi finite element method (FEM); and the design with the real soft magnetic material as image was proved suitable for simulating the ultrahigh density perpendicular recording write head.
基金financially supported by the National Natural Science Foundation of China (Nos.61227902, 11274033, and 11074101)
文摘Owing to the epitaxial inducement of Au atom,Au interlayer was introduced to increase the perpendicular anisotropy and the coercivity in L10-FePt nanocomposite film.Micromagnetics can be used to reveal the relationship between microstructure and magnetic properties of materials,and give the information of the perpendicular anisotropy and coercivity.In this work,the effect of the Au interlayer on annealed[Fe（0.5 nm）/Pt（0.5 nm）/Au（d nm）]10 nanocomposite recording medium by a micromagnetic model was studied.The model contains three phases：hard magnetic phase,soft magnetic phase,and nonmagnetic phase.The calculated result shows that perpendicular orientation degree of the texture and proportion of a hard magnetic phase to the total phase in the annealed film are both enhanced by increasing Au interlayer thickness.This result can be conducive to the improvement of the perpendicular anisotropy and the coercivity of the FePt nanocomposite film in the experiments.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50801033)
文摘The effects of the number and the location of notches on the formation of flux-closure states in bi-rings with fields applied in the x direction （i.e., along the short axis direction of hi-rings） and y direction （i.e., along the long axis direction of bi-rings） are investigated using micromagnetic simulation. For the bi-rings with one notch and the bi-rings with two notches symmetric about y axis, the order of flux-closure state formation in each ring can be controlled. But the flux-closure state forms simultaneously in each ring for the bi-rings with two notches symmetric about x axis. For the bi-rings with two notches that are symmetric neither about x axis nor about y axis, only one ring can form a flux- closure state in the y-direction field and no fluxclosure state can be found in rings in the x-direction field. Therefore, logic states can be defined by controlling the order of flux-closure state formation, which can be utilized in future logic devices.
基金Project supported by the Key Program of the National Natural Science Foundation of China(Grant No.51331003)the International S&T Cooperation Program of China(Grant No.2015DFG52020)+1 种基金the General Program of Science and Technology Development Project of Beijing Municipal Education Commission,China(Grant No.KM201710005006)the State Key Laboratory of Advanced Metals and Materials,China(Grant No.2015-ZD02)
文摘In this study, micromagnetism simulation by using timte dltterence method is cameo out on the Ncl21-el415/a-Fe nanocomposite magnet with soft phase imbedded in hard phase. The effects of soft magnetic phase size （S） on the magnetic properties and magnetic reversal modes are systematically analyzed. As S increases from 1 nm to 48 nm, the remanence （Jr） increases, while the coercivity （Hci） decreases, leading to the result that the magnetic energy prod- uct [（BH）max] first increases slowly, and then decreases rapidly, peaking at S = 24 nm with the （BH）max of 72.9 MGOe （1 MGOe = 7.95775 kJ.m-3）. Besides, with the increase of S, the coercivity mechanism of the nanocomposite magnet changes from nucleation to pinning. Furthermore, by observing the magnetic moment evolution in demagnetization pro- cess, the magnetic reversal of the soft phase in the nanocomposite magnet can be divided into three modes with the increase of S： coherent rotation （S 〈 3 nm）, quasi-coherent rotation （3 nm≤S 〈 36 nm）, and the vortex-like rotation （S ≥36 nm）.
基金the Natural Science Foundation of Shandong Province(Grant No.ZR2022MA053),the National Natural Science Foundation of China(Grant Nos.11704211,11847233,52301255,12205157,and 12205093)the Funda-mental Research Funds for the Central Universities(Grant No.lzujbky-2022-kb01)+2 种基金China and Germany Postdoctoral Exchange Program(Helmholtz-OCPC)China Postdoctoral Science Foundation(Grant No.2018M632608)Applied Basic Research Project of Qingdao(Grant No.18-2-2-16-jcb).
文摘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.
基金Project supported by the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2021B0101300003)the Guangdong Basic and Applied Basic Research Foundation,China(Grant Nos.2022A1515110863 and 2023A1515010837)+5 种基金the National Key Research and Development Program of China(Grant No.2016YFA0300803)the National Natural Science Foundation of China(Grant Nos.12304136,61427812,11774160,12241403,51771127,52171188,and 52111530143)the Natural Science Foundation of Jiangsu Province,China(Grant Nos.BK20192006 and BK20200307)the Fundamental Research Funds for the Central Universities,China(Grant No.021014380113)International Exchanges 2020 Cost Share(NSFC),China(Grant No.IECNSFC201296)the Project for Maiden Voyage of Guangzhou Basic and Applied Basic Research Scheme,China(Grant No.2024A04J4186)。
文摘Skyrmions, with their vortex-like structures and inherent topological protection, play a pivotal role in developing innovative low-power memory and logic devices. The efficient generation and control of skyrmions in geometrically confined systems are crucial for the development of skyrmion-based spintronic devices. In this study, we focus on investigating the non-reciprocal transport behavior of skyrmions and their interactions with boundaries of various shapes. The shape of the notch structure in the nanotrack significantly affects the dynamic behavior of magnetic skyrmions. Through micromagnetic simulation, the non-reciprocal transport properties of skyrmions in nanowires with different notch structures are investigated in this work.
基金Project supported by the National Key R&D Program of China(Grant Nos.2021YFB3502400 and 2022YFA1403601)the National Natural Science Foundation of China(Grant Nos.12274204,12274203,51831005,52172270,11974165,92165103,51971110,12004329,and 12241402).
文摘Recent theory and experiments show that artificial magnetic skyrmions can be stabilized at room temperature without the need for the external magnetic field,casting strong potentials for the device applications.In this work,we study the electric field manipulation of artificial magnetic skyrmions imprinted by Co disks on CoPt multilayers utilizing the micromagnetic simulations.We find that the reversible annihilation and creation of skyrmions can be realized with the electric field via the strain mediated magnetoelastic coupling.In addition,we also demonstrate controllable manipulation of individual skyrmion,which opens a new platform for constructing magnetic field-free and low-energy dissipation skyrmion based media.
