The multilayers in the forms of glass/Cu(Ni)(5.0 nm)/[Co(2.0 nm)/Cu(Ni)(0.5～3.7 nm)] 30 and glass/Ti(5.0 nm)/[Co(2.0 nm)/Ti(0.4～3.5 nm)] 30 ,prepared by dual facing target sputtering at room temperature,exh...The multilayers in the forms of glass/Cu(Ni)(5.0 nm)/[Co(2.0 nm)/Cu(Ni)(0.5～3.7 nm)] 30 and glass/Ti(5.0 nm)/[Co(2.0 nm)/Ti(0.4～3.5 nm)] 30 ,prepared by dual facing target sputtering at room temperature,exhibit a soft magnetic property.The structural and magnetic properties of Co/Cu(Ni) and Co/Ti multilayers were examined as a function of the spacer layer thickness (d Ti and d Cu(Ni) ) by low angle X ray diffraction (LAXRD) and VSM measurements.The saturation magnetization M s of the Co/Ti multilayers was found to decrease with d Ti and approached to a constant value when d Ti was thick enough.But in the Co/Cu(Ni) multilayers,the M s was found to oscillate with d Cu(Ni) when d Cu(Ni) was less than 3.0 nm,and the oscillation period was about 1.0 nm.This arose from the different interlayer magnetic coupling effects.We interpret these two different kinds of interlayer magnetic couplings as the consequence of the competition between the RKKY like and superexchange couplings.展开更多
The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresp...The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresponding four frequencie in middle of energy gaps exist in the magnon band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the four frequencies in middle of the energy gaps. When all interlayer exchange couplings are same, the effect of spin quantum numbers on the frequency wg1 in middle of the energy gap Δw12 is complicated, and the frequency wg1 depends on the match of spin quantum numbers in each layer. Meanwhile, the frequencies wg2, wg3, and wg4 in middle of other energy gaps increase monotonously with increasing spin quantum numbers. When the spin quantum numbers in each layer are same, the frequencies wg1, wg2, wg3, and wg4 all increase monotonously with increasing interlayer exchange couplings.展开更多
Spin-wave theory is used to study magnetic properties of ferromagnetic double layers with a ferrimagnetic interlayer coupling at zero temperature. The spin-wave spectra and four sublattices magnetizations and internal...Spin-wave theory is used to study magnetic properties of ferromagnetic double layers with a ferrimagnetic interlayer coupling at zero temperature. The spin-wave spectra and four sublattices magnetizations and internal energy are calculated by employing retarded Green function technique. The sublattice magnetizations at ground state are smaller than their classical values, owing to the zero-point quantum fluctuations of the spins.展开更多
The specific heats of both a two-layer ferromagnetic superlattice and a two-layer ferrimagnetic one arestudied.It is found that the spin quantum numbers,the interlayer and intralayer exchange couplings,the anisotropy,...The specific heats of both a two-layer ferromagnetic superlattice and a two-layer ferrimagnetic one arestudied.It is found that the spin quantum numbers,the interlayer and intralayer exchange couplings,the anisotropy,theapplied magnetic field,and the temperature all affect the specific heat of these superlattices.For both the ferromagneticand ferrimagnetic superlattices,the specific heat decreases with increasing the spin quantum number,the absolutevalue of interlayer exchange coupling,intralayer exchange coupling,and anisotropy,while it increases with increasingtemperature at low temperatures.When an applied magnetic field is enhanced,the specific heat decreases in the two-layerferromagnetic superlattice,while it is almost unchanged in the two-layer ferrimagnetic superlattice at low fieldrange at low temperatures.展开更多
The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, whic...The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, which is one of the most challenging scientific problems in the geospace weather study. The nonlinearity, multiple component, and time-dependent nature of the geospace make it very difficult to describe the physical process in geospace using traditional analytic analysis approach. Numerical simulations, a new research tool developed in recent decades, have a deep impact on the theory and application of the geospace. MHD simulations started at the end of the 1970s, and the initial study was limited to two-dimensional (2D) cases. Due to the intrinsic three-dimensional (3D) characteristics of the geospace, 3D MHD simulations emerged in the 1980s, in an attempt to model the large-scale structures and fundamental physical processes in the magnetosphere. They started to combine with the space exploration missions in the 1990s and make comparisons with observations. Physics-based space weather forecast models started to be developed in the 21st century. Currently only a few space-power countries such as USA and Japan have developed 3D magnetospheric MHD models. With the rapid advance of space science in China, we have developed a new global MHD model, namely PPMLR-MHD, which has high order spatial accuracy and low numerical dissipation. In this review, we will briefly introduce the global 3D MHD modeling, especially the PPMLR-MHD code, and summarize our recent work based on the PPMLR-MHD model, with an emphasis on the interaction of interplanetary shocks with the magnetosphere, large-scale current systems, reconnection voltage and transpolar potential drop, and Kelvin-Helmholtz (K-H) instability at the magnetopause.展开更多
文摘The multilayers in the forms of glass/Cu(Ni)(5.0 nm)/[Co(2.0 nm)/Cu(Ni)(0.5～3.7 nm)] 30 and glass/Ti(5.0 nm)/[Co(2.0 nm)/Ti(0.4～3.5 nm)] 30 ,prepared by dual facing target sputtering at room temperature,exhibit a soft magnetic property.The structural and magnetic properties of Co/Cu(Ni) and Co/Ti multilayers were examined as a function of the spacer layer thickness (d Ti and d Cu(Ni) ) by low angle X ray diffraction (LAXRD) and VSM measurements.The saturation magnetization M s of the Co/Ti multilayers was found to decrease with d Ti and approached to a constant value when d Ti was thick enough.But in the Co/Cu(Ni) multilayers,the M s was found to oscillate with d Cu(Ni) when d Cu(Ni) was less than 3.0 nm,and the oscillation period was about 1.0 nm.This arose from the different interlayer magnetic coupling effects.We interpret these two different kinds of interlayer magnetic couplings as the consequence of the competition between the RKKY like and superexchange couplings.
基金Supported by the Natural Science Foundation of Liaoning Province of China under Grant No. 20062040
文摘The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresponding four frequencie in middle of energy gaps exist in the magnon band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the four frequencies in middle of the energy gaps. When all interlayer exchange couplings are same, the effect of spin quantum numbers on the frequency wg1 in middle of the energy gap Δw12 is complicated, and the frequency wg1 depends on the match of spin quantum numbers in each layer. Meanwhile, the frequencies wg2, wg3, and wg4 in middle of other energy gaps increase monotonously with increasing spin quantum numbers. When the spin quantum numbers in each layer are same, the frequencies wg1, wg2, wg3, and wg4 all increase monotonously with increasing interlayer exchange couplings.
基金supported by the Natural Science Foundation of Liaoning Province under Grant No.20041021the Scientific Foundation of the Educational Department of Liaoning Province under Grant Nos.2004C006 and 20060638the Postdoctoral Foundation of Shenyang University of Technology
文摘Spin-wave theory is used to study magnetic properties of ferromagnetic double layers with a ferrimagnetic interlayer coupling at zero temperature. The spin-wave spectra and four sublattices magnetizations and internal energy are calculated by employing retarded Green function technique. The sublattice magnetizations at ground state are smaller than their classical values, owing to the zero-point quantum fluctuations of the spins.
基金Supported by the Natural Science Foundation of Liaoning Province of China under Grant No.20062040
文摘The specific heats of both a two-layer ferromagnetic superlattice and a two-layer ferrimagnetic one arestudied.It is found that the spin quantum numbers,the interlayer and intralayer exchange couplings,the anisotropy,theapplied magnetic field,and the temperature all affect the specific heat of these superlattices.For both the ferromagneticand ferrimagnetic superlattices,the specific heat decreases with increasing the spin quantum number,the absolutevalue of interlayer exchange coupling,intralayer exchange coupling,and anisotropy,while it increases with increasingtemperature at low temperatures.When an applied magnetic field is enhanced,the specific heat decreases in the two-layerferromagnetic superlattice,while it is almost unchanged in the two-layer ferrimagnetic superlattice at low fieldrange at low temperatures.
基金supported by the National Basic Research Program of China (Grant No.2012CB825602)National Natural Science Foundation of China (Grant Nos.41204118 & 41231067)in part by the Specialized Research Fund for State Key Laboratories of China
文摘The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, which is one of the most challenging scientific problems in the geospace weather study. The nonlinearity, multiple component, and time-dependent nature of the geospace make it very difficult to describe the physical process in geospace using traditional analytic analysis approach. Numerical simulations, a new research tool developed in recent decades, have a deep impact on the theory and application of the geospace. MHD simulations started at the end of the 1970s, and the initial study was limited to two-dimensional (2D) cases. Due to the intrinsic three-dimensional (3D) characteristics of the geospace, 3D MHD simulations emerged in the 1980s, in an attempt to model the large-scale structures and fundamental physical processes in the magnetosphere. They started to combine with the space exploration missions in the 1990s and make comparisons with observations. Physics-based space weather forecast models started to be developed in the 21st century. Currently only a few space-power countries such as USA and Japan have developed 3D magnetospheric MHD models. With the rapid advance of space science in China, we have developed a new global MHD model, namely PPMLR-MHD, which has high order spatial accuracy and low numerical dissipation. In this review, we will briefly introduce the global 3D MHD modeling, especially the PPMLR-MHD code, and summarize our recent work based on the PPMLR-MHD model, with an emphasis on the interaction of interplanetary shocks with the magnetosphere, large-scale current systems, reconnection voltage and transpolar potential drop, and Kelvin-Helmholtz (K-H) instability at the magnetopause.
