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1.
纳米级自旋电子学材料取得重要进展 总被引:1,自引:0,他引:1
因为纳米级的自旋电子学器件需要在纳米尺度上仍能在较高温度下保持优异性能的高自旋极化率材料,故与半导体相容的半金属铁磁体近来受到高度重视.文章介绍作者在这个方向上研究工作的最新重要进展:通过大规模系统的高精度第一原理计算,作者发现三个3d过渡金属硫系化合物的闪锌矿相具有优异的半金属铁磁性,并且其结构性能适合做成具有足够厚度的薄膜或层状材料,便于应用于纳米级自旋电子学器件。 相似文献
2.
For decades the research on thin-film growth has attracted considerable attention as these kinds of materials have the potential for a new generation of device application. It is known that the nuclei at the initial stage of the islands are more stable than others and certain atoms are inert while others are active. In this paper, by using kinetic Monte Carlo simulations, we will show that, when a surfactant layer is used to mediate the growth, a counter-intuitive fractal-to-compact island shape transition can be induced by increasing deposition flux or decreasing growth temperature. Specifically, we introduce a reaction-limited aggregation (RLA) theory, where the physical process controlling the island shape transition is the shielding effect of adatoms stuck to the stable islands on the incoming adatoms. Moreover, the origin of a transition from triangular to hexagonal and then to inverted triangular as well as the decay characteristics of three-dimensional islands on the surface and relations of our unique predictions with recent experiments will be discussed. Furthermore, we will present a novel idea to make use of the condensation energy of adatoms to control the island evolution along a special direction. 相似文献
3.
First-principles investigation of electronic structure,effective carrier masses,and optical properties of ferromagnetic semiconductor CdCr_2S_4 下载免费PDF全文
The electronic structures, the effective masses, and optical properties of spinel CdCr_2S_4 are studied by using the fullpotential linearized augmented planewave method and a modified Becke–Johnson exchange functional within the densityfunctional theory. Most importantly, the effects of the spin–orbit coupling(SOC) on the electronic structures and carrier effective masses are investigated. The calculated band structure shows a direct band gap. The electronic effective mass and the hole effective mass are analytically determined by reproducing the calculated band structures near the BZ center.SOC substantially changes the valence band top and the hole effective masses. In addition, we calculated the corresponding optical properties of the spinel structure CdCr_2S_4. These should be useful to deeply understand spinel CdCr_2S_4 as a ferromagnetic semiconductor for possible semiconductor spintronic applications. 相似文献
4.
Quantum Monte Carlo study on the phase transition for a generalized two-dimensional staggered dimerized Heisenberg model 下载免费PDF全文
In order to gain a deeper understanding of the quantum criticality in the explicitly staggered dimerized Heisenberg models,we study a generalized staggered dimer model named the J0-J1-J2 model,which corresponds to the staggered J-J ' model on a square lattice and a honeycomb lattice when J1/J0 equals 1 and 0,respectively.Using the quantum Monte Carlo method,we investigate all the quantum critical points of these models with J1/J0 changing from 0 to 1 as a function of coupling ratio α=J2/J0.We extract all the critical values of the coupling ratio αc for these models,and we also obtain the critical exponents ν,β/ν,and η using different finite-size scaling anstz,.All these exponents are not consistent with the three-dimensional Heisenberg universality class,indicating some unconventional quantum ciritcial points in these models. 相似文献
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A Green's function model for ferromagnetism and spin excitations of (Ga,Mn)As diluted magnetic semiconductors 下载免费PDF全文
We study (Ga, Mn)As diluted magnetic semiconductors in
terms of the Ruderman--Kittel--Kasuya--Yosida quantum spin model in
Green's function approach. Random distributions of the magnetic
atoms are treated by using an analytical average of magnetic
configurations. Average magnetic moments and spin excitation spectra
as functions of temperature can be obtained by solving
self-consistent equations, and the Curie temperature TC is
given explicitly. TC is proportional to magnetic atomic
concentration, and there exists a maximum for TC as a
function of carrier concentration. Applied to (Ga, Mn)As, the
theoretical results are consistent with experiment and the
experimental TC can be obtained with reasonable parameters.
This modelling can also be applied to other diluted magnetic
semiconductors. 相似文献
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Electronic structure and magnetic and optical properties of double perovskite Bi2 FeCrO6 from first-principles investigation 下载免费PDF全文
Double perovskite Bi2 FeCrO6 , related with multiferroic BiFeO3 , is very interesting because of its strong ferroelectricity and high magnetic Curie temperature beyond room temperature. We investigate its electronic structure and magnetic and optical properties by using a full-potential density-functional method. Our optimization shows that it is a robust ferrimagnetic semiconductor. This nonmetallic phase is formed due to crystal field splitting and spin exchange splitting, in contrast to previous studies. Spin exchange constants and optical properties are calculated. Our Monte Carlo magnetic Curie temperature is 450 K, much higher than any previously calculated value and consistent with experimental results. Our study and analysis reveal that the main magnetic mechanism is an antiferromagnetic superexchange between Fe and Cr over the intermediate O atom. These results are useful in understanding such perovskite materials and exploring their potential applications. 相似文献
9.
Density-functional theory investigation of energy gaps and optical properties of Hg1-xCdxTe and In1-xGaxAs 下载免费PDF全文
We use a modified Becke-Johnson exchange plus a local density approximation correlation potential within the density functional theory to investigate the electronic structures of Hg1-xCdxTe and In1-xGaxAs with x being 0, 0.25, 0.5, 0.75, and 1. For both of the two series, our calculated energy gaps and dielectric functions (real part ε1 and imaginary part ε2) are in agreement with the corresponding experimental results with x being between 0 and 1. The calculated zero-frequency refractive index varies greatly with x for Hg1-xCdxTe, but changes little with x for In1-xGaxAs, which is consistent with the real parts of their dielectric functions. Therefore, this new approach is satisfactory to describe the electronic structures and the optical properties of the semiconductors. 相似文献
10.
Electronic structures and optical properties of TiO2:Improved density-functional-theory investigation 下载免费PDF全文
TiO2 has been recently used to realize high-temperature ferromagnetic semiconductors.In fact,it has been widely used for a long time as white pigment and sunscreen because of its whiteness,high refractive index,and excellent optical properties.However,its electronic structures and the related properties have not been satisfactorily understood.Here,we use Tran and Blaha's modified Becke-Johnson(TB-mBJ) exchange potential(plus a local density approximation correlation potential) within the density functional theory to investigate electronic structures and optical properties of rutile and anatase TiO2.Our comparative calculations show that the energy gaps obtained from mBJ method agree better with the experimental results than that obtained from local density approximation(LDA) and generalized gradient approximation(GGA),in contrast with substantially overestimated values from many-body perturbation(GW) calculations.As for optical dielectric functions(both real and imaginary parts),refractive index,and extinction coefficients as functions of photon energy,our mBJ calculated results are in excellent agreement with the experimental curves.Our further analysis reveals that these excellent improvements are achieved because mBJ potential describes accurately the energy levels of Ti 3d states.These results should be helpful to understand the high temperature ferromagnetism in doped TiO2.This approach can be used as a standard to understand electronic structures and the related properties of such materials as TiO2. 相似文献