Confronted with severe electromagnetic wave pollution,the development of high-performance electromagnetic wave shielding or absorbing materials is an effective way to deal with it.Notably,double transition metal alloy...Confronted with severe electromagnetic wave pollution,the development of high-performance electromagnetic wave shielding or absorbing materials is an effective way to deal with it.Notably,double transition metal alloys and transition metal dichalcogenides have attracted extensive attention in electromagnetic wave absorption,but few reports have studied the effects of these two materials on electromagnetic wave absorption at the same time.In this work,cobalt-based alloy with magnetic loss mechanism was selected for composition optimization.The ternary metal-organic framework was prepared by the one-step method,and then CoCu/C was prepared by high temperature annealing.Finally,in the hydrothermal process,ultra-thin tungsten selenide nanosheets were coated on the surface of magnetic component,and the final polyhedral WSe_(2)/CoCu/C composites with multiple heterogeneous interfaces were obtained.The synergistic effect of dielectric and magnetic components optimizes impedance matching and allows more electromagnetic waves to enter the absorber.Subsequently,through the conduction loss of high conductivity graphitized carbon,interfacial polarization,and dipole polarization of heterogeneous interfaces between the components,the magnetic loss provided by CoCu alloy can work together to maximize the attenuation ability of electromagnetic waves.Exactly,the minimum reflection loss(RLmin)value of the composite reaches-53.43 dB when the matched thickness is 2.1 mm,while the maximum effective absorption bandwidth(EABmax)reaches 6.0 GHz at a thin thickness of 1.8 mm.This work provides some support and reference for the design of novel electromagnetic wave absorbing materials via the dielectric/magnetic loss synergistic mechanism.展开更多
We have investigated the magnetic transition and magnetocaloric effects of Mn1＋xCo1-xGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferr...We have investigated the magnetic transition and magnetocaloric effects of Mn1＋xCo1-xGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature. Further increasing the content of Mn （x = 0.11） gives rise to a single second-order magnetic transition. Interestingly, large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys. The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper.展开更多
The magnetic properties,magnetic phase transition and magnetocaloric effects(MCE) of Er_(3)Si_(2)C_(2) compound were investigated based on theoretical calculations and experimental analysis.Based on the first principl...The magnetic properties,magnetic phase transition and magnetocaloric effects(MCE) of Er_(3)Si_(2)C_(2) compound were investigated based on theoretical calculations and experimental analysis.Based on the first principles calculations,the antiferromagnetic(AFM) ground state type in Er_(3)Si_(2)C_(2) compound was predicted and its electronic structure was investigated.The experimental results show that Ei_(3)Si_(2)C_(2) compound is an AFM compound with the Neel temperature(T_(N) of 7 K and undergoes a field-induced firstorder magnetic phase transition from AFM to ferromagnetic(FM) under magnetic fields exceeding 0.6 T at 2 K.The magnetic transition process of Er_(3)Si_(2)C_(2) compound was investigated and discussed.The values of the maximum magnetic entropy change(-ΔS_(M)^(max)) and the refrigeration capacity(RC) are 17 J/(kg·K)and 193 J/kg under changing magnetic fields of 0-5 T,respectively.As a potential cryogenic magnetic refrigerant,the Er_(3)Si_(2)C_(2) compound also provides an interesting research medium to study the magnetic phase transition process.展开更多
Long-range magnetic order appears on a side decorated Heisenberg spin nanoribbon at nonzero temperature,although no spontaneous magnetization exists in a one-or two-dimensional isotropic Heisenberg model at any nonzer...Long-range magnetic order appears on a side decorated Heisenberg spin nanoribbon at nonzero temperature,although no spontaneous magnetization exists in a one-or two-dimensional isotropic Heisenberg model at any nonzero temperature according to the Mermin-Wagner theorem.By use of the spin Green's function method,we calculated the magnetizations of Heisenberg nanoribbons decorated by side spins with single-ion anisotropy and found that the system exhibits a nonzero transition temperature,whether the decorated edge spins of the system link together or separate from each other.When the width of the nanoribbon achieves infinite limit,the transition temperatures of the system tend to the same finite constant eventually whether one edge or both edges are decorated by side spins in the nanoribbon.The results reveal that the magnetism of a low-dimensional spin system is different from that of a threedimensional spin system.When the single-ion anisotropy of edge spins in a Heisenberg spin nanoribbon can be modulated by an electric field experimentally,various useful long-range magnetic orders of the system can be obtained.This work can provide a detailed theoretical basis for designing and fabricating next-generation low-dimensional magnetic random-access memory.展开更多
The effect of Fe on microstructure and magnetic thermal performance of LaFel 1.6.xSil.4 alloys were studied by X-ray dif- fraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）,...The effect of Fe on microstructure and magnetic thermal performance of LaFel 1.6.xSil.4 alloys were studied by X-ray dif- fraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and vibrating-sample magnetometer （VSM）, respectively. The results showed that the excess Fe would make the 1：13 phase reduce in proportion and the easy corrosion phase LaFeSi phase disappear in LaFelL6＊xSil.4 alloys. The LaFel 1.6.xSil.4 alloys kept the first order magnetic phase transition, and the maximum isothermal magnetic entropy changed and the relative cooling power reached the maximum in LaFel 1.6,xSil.4 alloys with x=1.05 and 1.1, respectively.展开更多
As an intrinsic magnetic topological insulator with magnetic order and non-trivial topological structure,MnBi_(2)Te_(4)is an ideal material for studying exotic topological states such as quantum anomalous Hall effect ...As an intrinsic magnetic topological insulator with magnetic order and non-trivial topological structure,MnBi_(2)Te_(4)is an ideal material for studying exotic topological states such as quantum anomalous Hall effect and topological axion insulating states.Here,we carry out magnetic and electrical transport measurements on(Mn1–xGex)Bi_(2)Te_(4)(x=0,0.15,0.30,0.45,0.60,and 0.75)single crystals.It is found that with increasing x,the dilution of magnetic moments gradually weakens the antiferromagnetic exchange interaction.Moreover,Ge doping reduces the critical field of ferromagnetic ordering,which may provide a possible way to implement the quantum anomalous Hall effect at lower magnetic field.Electrical transport measurements suggest that electrons are the dominant charge carriers,and the carrier density increases with the Ge doping ratio.Additionally,the Kondo effect is observed in the samples with x=0.45,0.60,and 0.75.Our results suggest that doping germanium is a viable way to tune the magnetic and electrical transport properties of MnBi_(2)Te_(4),opening up the possibility of future applications in magnetic topological insulators.展开更多
Control over magnetic properties by optical stimulation is not only interesting from the physics point of view,but also important for practical applications such as magneto-optical devices.Here,based on a simple tight...Control over magnetic properties by optical stimulation is not only interesting from the physics point of view,but also important for practical applications such as magneto-optical devices.Here,based on a simple tight-binding(TB)model,we propose a general theory of light-induced magnetic phase transition(MPT)in antiferromagnets.Considering the fact that the bandgap of the antiferromagnetic(AFM)phase is usually larger than that of the ferromagnetic(FM)one for a given system,we suggest that light-induced electronic excitation prefers to stabilize the FM state over the AFM one,and will induce an MPT from AFM phase to FM phase once a critical photocarrier concentration(αc)is reached.This theory has been confirmed by performing firstprinciples calculations on a series of 2D van der Waals(vd W)antiferromagnets.Interestingly,a linear relationship betweenαc and the intrinsic material parameters is obtained,in agreement with our TB model analysis.Our general theory paves a new way to manipulate 2D magnetism with high speed and superior resolution.展开更多
As typical strongly correlated electronic materials, manganites show rich magnetic phase diagrams and electronic structures depending on the doped carrier density. Most previous relevant studies of doped manganites re...As typical strongly correlated electronic materials, manganites show rich magnetic phase diagrams and electronic structures depending on the doped carrier density. Most previous relevant studies of doped manganites rely on the cubic/orthorhombic structures, while the hexagonal structure is much less studied. Here first-principles calculations are employed to investigate the magnetic and electronic structures of La-doped 4H-SrMnO_(3). By systematically analyzing the two kinds of La-doped positions, our calculations predict that the doped electron with lattice distortion would prefer to form polarons, which contribute to the local magnetic phase transition, nonzero net magnetization, and semiconducting behavior. In addition, the energy gap decreases gradually with increasing doping concentration, indicating a tendency of insulator–metal transition.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52377026 and 52301192)the Natural Science Foundation of Shandong Province(No.ZR2019YQ24)+4 种基金the Taishan Scholars and Young Experts Program of Shandong Province(No.tsqn202103057)the Qingchuang Talents Induction Program of Shandong Higher Education Institution(Research and Innovation Team of Structural-Functional Polymer Composites)the Key Laboratory of Engineering Dielectrics and Its Application(Harbin University of Science and Technology)the Ministry of Educationthe Special Financial of Shandong Province(Structural Design of High-efficiency Electromagnetic Wave-absorbing Composite Materials and Construction of Shandong Provincial Talent Teams).
文摘Confronted with severe electromagnetic wave pollution,the development of high-performance electromagnetic wave shielding or absorbing materials is an effective way to deal with it.Notably,double transition metal alloys and transition metal dichalcogenides have attracted extensive attention in electromagnetic wave absorption,but few reports have studied the effects of these two materials on electromagnetic wave absorption at the same time.In this work,cobalt-based alloy with magnetic loss mechanism was selected for composition optimization.The ternary metal-organic framework was prepared by the one-step method,and then CoCu/C was prepared by high temperature annealing.Finally,in the hydrothermal process,ultra-thin tungsten selenide nanosheets were coated on the surface of magnetic component,and the final polyhedral WSe_(2)/CoCu/C composites with multiple heterogeneous interfaces were obtained.The synergistic effect of dielectric and magnetic components optimizes impedance matching and allows more electromagnetic waves to enter the absorber.Subsequently,through the conduction loss of high conductivity graphitized carbon,interfacial polarization,and dipole polarization of heterogeneous interfaces between the components,the magnetic loss provided by CoCu alloy can work together to maximize the attenuation ability of electromagnetic waves.Exactly,the minimum reflection loss(RLmin)value of the composite reaches-53.43 dB when the matched thickness is 2.1 mm,while the maximum effective absorption bandwidth(EABmax)reaches 6.0 GHz at a thin thickness of 1.8 mm.This work provides some support and reference for the design of novel electromagnetic wave absorbing materials via the dielectric/magnetic loss synergistic mechanism.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 50701022,51001019,and 50831006)the Program for New Century Excellent Talents of China (Grant No. NCET-08-0278)
文摘We have investigated the magnetic transition and magnetocaloric effects of Mn1＋xCo1-xGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature. Further increasing the content of Mn （x = 0.11） gives rise to a single second-order magnetic transition. Interestingly, large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys. The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper.
基金supported by the National Key Research and Development Program of China (2021YFB3501204)the National Science Foundation for Excellent Young Scholars (52222107)+2 种基金the National Science Foundation for Distinguished Young Scholars (51925605)the National Natural Science Foundation of China (52171195)Projects of Ganjiang Innovation Academy,Chinese Academy of Sciences (E055B002)。
文摘The magnetic properties,magnetic phase transition and magnetocaloric effects(MCE) of Er_(3)Si_(2)C_(2) compound were investigated based on theoretical calculations and experimental analysis.Based on the first principles calculations,the antiferromagnetic(AFM) ground state type in Er_(3)Si_(2)C_(2) compound was predicted and its electronic structure was investigated.The experimental results show that Ei_(3)Si_(2)C_(2) compound is an AFM compound with the Neel temperature(T_(N) of 7 K and undergoes a field-induced firstorder magnetic phase transition from AFM to ferromagnetic(FM) under magnetic fields exceeding 0.6 T at 2 K.The magnetic transition process of Er_(3)Si_(2)C_(2) compound was investigated and discussed.The values of the maximum magnetic entropy change(-ΔS_(M)^(max)) and the refrigeration capacity(RC) are 17 J/(kg·K)and 193 J/kg under changing magnetic fields of 0-5 T,respectively.As a potential cryogenic magnetic refrigerant,the Er_(3)Si_(2)C_(2) compound also provides an interesting research medium to study the magnetic phase transition process.
文摘Long-range magnetic order appears on a side decorated Heisenberg spin nanoribbon at nonzero temperature,although no spontaneous magnetization exists in a one-or two-dimensional isotropic Heisenberg model at any nonzero temperature according to the Mermin-Wagner theorem.By use of the spin Green's function method,we calculated the magnetizations of Heisenberg nanoribbons decorated by side spins with single-ion anisotropy and found that the system exhibits a nonzero transition temperature,whether the decorated edge spins of the system link together or separate from each other.When the width of the nanoribbon achieves infinite limit,the transition temperatures of the system tend to the same finite constant eventually whether one edge or both edges are decorated by side spins in the nanoribbon.The results reveal that the magnetism of a low-dimensional spin system is different from that of a threedimensional spin system.When the single-ion anisotropy of edge spins in a Heisenberg spin nanoribbon can be modulated by an electric field experimentally,various useful long-range magnetic orders of the system can be obtained.This work can provide a detailed theoretical basis for designing and fabricating next-generation low-dimensional magnetic random-access memory.
基金supported by China Postdoctoral Science Foundation(2013M542274)
文摘The effect of Fe on microstructure and magnetic thermal performance of LaFel 1.6.xSil.4 alloys were studied by X-ray dif- fraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and vibrating-sample magnetometer （VSM）, respectively. The results showed that the excess Fe would make the 1：13 phase reduce in proportion and the easy corrosion phase LaFeSi phase disappear in LaFelL6＊xSil.4 alloys. The LaFel 1.6.xSil.4 alloys kept the first order magnetic phase transition, and the maximum isothermal magnetic entropy changed and the relative cooling power reached the maximum in LaFel 1.6,xSil.4 alloys with x=1.05 and 1.1, respectively.
基金supported by the National Key Research and Development Program of China(2022YFB3505101)the National Science Foundation for Excellent Young Scholars(52222107)+2 种基金the National Science Foundation for Distinguished Young Scholars(51925605)the Research Projects of Ganjiang Innovation Academy,Chinese Academy of Sciences(E055B002)the Doctoral Postgraduate Innovation Funding project of Hebei Province(CXZZBS2023032)。
基金the National Key R&D Program of China(Grant No.2018YFA0704300)the Natural Science Foundation of Jiangsu Province of China(Grant No.BK20201285).
文摘As an intrinsic magnetic topological insulator with magnetic order and non-trivial topological structure,MnBi_(2)Te_(4)is an ideal material for studying exotic topological states such as quantum anomalous Hall effect and topological axion insulating states.Here,we carry out magnetic and electrical transport measurements on(Mn1–xGex)Bi_(2)Te_(4)(x=0,0.15,0.30,0.45,0.60,and 0.75)single crystals.It is found that with increasing x,the dilution of magnetic moments gradually weakens the antiferromagnetic exchange interaction.Moreover,Ge doping reduces the critical field of ferromagnetic ordering,which may provide a possible way to implement the quantum anomalous Hall effect at lower magnetic field.Electrical transport measurements suggest that electrons are the dominant charge carriers,and the carrier density increases with the Ge doping ratio.Additionally,the Kondo effect is observed in the samples with x=0.45,0.60,and 0.75.Our results suggest that doping germanium is a viable way to tune the magnetic and electrical transport properties of MnBi_(2)Te_(4),opening up the possibility of future applications in magnetic topological insulators.
基金supported by the National Natural Science Foundation of China(Grant Nos.11991061,11825403,and 12188101)the Guangdong Major Project of Basic and Applied Basic Research(Future functional materials under extreme conditions-2021B0301030005)the support from the National Natural Science Foundation of China(NSAF,Grant No.U1930402)。
文摘Control over magnetic properties by optical stimulation is not only interesting from the physics point of view,but also important for practical applications such as magneto-optical devices.Here,based on a simple tight-binding(TB)model,we propose a general theory of light-induced magnetic phase transition(MPT)in antiferromagnets.Considering the fact that the bandgap of the antiferromagnetic(AFM)phase is usually larger than that of the ferromagnetic(FM)one for a given system,we suggest that light-induced electronic excitation prefers to stabilize the FM state over the AFM one,and will induce an MPT from AFM phase to FM phase once a critical photocarrier concentration(αc)is reached.This theory has been confirmed by performing firstprinciples calculations on a series of 2D van der Waals(vd W)antiferromagnets.Interestingly,a linear relationship betweenαc and the intrinsic material parameters is obtained,in agreement with our TB model analysis.Our general theory paves a new way to manipulate 2D magnetism with high speed and superior resolution.
基金supported by the Natural Science Foundation of Nanjing University of Posts and Telecommunications (Grant Nos.NY222167 and NY220005)。
文摘As typical strongly correlated electronic materials, manganites show rich magnetic phase diagrams and electronic structures depending on the doped carrier density. Most previous relevant studies of doped manganites rely on the cubic/orthorhombic structures, while the hexagonal structure is much less studied. Here first-principles calculations are employed to investigate the magnetic and electronic structures of La-doped 4H-SrMnO_(3). By systematically analyzing the two kinds of La-doped positions, our calculations predict that the doped electron with lattice distortion would prefer to form polarons, which contribute to the local magnetic phase transition, nonzero net magnetization, and semiconducting behavior. In addition, the energy gap decreases gradually with increasing doping concentration, indicating a tendency of insulator–metal transition.
