Theoretical Study of Magnetism and Transport Properties in Diluted Magnetic Semiconductors

稀磁半导体磁性和输运特性的理论研究

基本信息

批准号：
17540339
负责人：
KUBO Kenn
金额：
$ 2.18万
依托单位：
Aoyama Gakuin University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-17540339/
关键词：
diluted magnetic semiconductors carrier induced ferromagnetism optical conductivity minimal model coherent potential approximation partial line graph flat energy band Hubbard model 強磁性引力ポテンシャル部分ライングラフ CPA フラットバンド部分強磁性輸送現象 /

项目摘要

1) We proposed a simplest model which contains essential features of the diluted magnetic semiconductors, which we call "minimal model". This model is a lattice model with randomly substituted with magnetic impurities with localized spins. Carriers hop among orbitals at lattice sites. An attractive Coulomb potential as well as an exchange interaction between a carrier spin and a localized spin exerts on a carrier at an impurity site. We investigated the model by use of the coherent potential approximation(CPA). As a result we found that the characteristic behavior of the magnetism can be categorized into the strong coupling or the weak coupling regime. In the weak coupling regime, the system can be described by the mean field picture and the ferromagnetism is realized in a wide region of carrier density though the Curie temperature is relatively low. In the strong coupling regime impurity bands are formed and the spins of carriers in the impurity bands are tightly bound to the localize … More d spins. Therefore the mechanism similar to the double-exchange interaction in manganum oxides is operative. As a result the ferromagnetism is realized only when the carrier density is less than the impurity concentration though the Curie temperature is relatively high. The Curie temperature saturates even the exchange coupling is increased extremely. We also studied the optical conductivity. The calculated results show that the Drude peak of the conductivity diminishes and finally vanishes when the coupling with the impurities is increased and another peak appears at a finite frequency. This agrees qualitatively with the experimental observations. The results on the direct conductivity show variety of behaviors in the temperature dependence according to the values of parameters, though we could not obtain good agreement with experimental results.2) Using numerical simulations, we examined the effect of the range of the Coulomb attractive potential due to impurities, which is assumed to be of contact-type in the minimal model. Though we could not simulate sufficiently large systems, our result for a cluster with 100 sites showed that the longer range of the potential leads to the broader impurity band. The result suggests that the long ranged potential leads to the higher Curie temperature.3) We proposed a class of lattice structures called "generalized partial line graph(GPLG)", on which tight-binding band structures realize flat bands. We investigated the magnetism in the Hubbard model on several examples of GPLG by use of exact diagonalization of finite clusters. Obtained results showed that the systems with GPLG lattice structures are promising candidates for realizing complete and partial ferromagnetism, ferrimagnetism and antiferromagnetism. Less

1）我们提出了一个最简单的模型，其中包含稀释磁性半导体的基本特征，我们称之为“最小模型”。该模型是一个晶格模型，其随机用磁性杂质随机取代。载体在晶格站点跳跃。在杂质部位的载体上施加载体和局部旋转之间的吸引人的库仑电位以及固定旋转之间的交换相互作用。我们通过使用相干电位近似（CPA）研究了该模型。结果，我们发现磁性的特征行为可以分为强耦合或弱耦合方案。在弱耦合方案中，可以通过平均场图来描述系统，尽管居里温度相对较低，但在较广泛的载体密度区域中实现了铁磁性。在强的耦合方案中，形成了杂质带，并且杂质带中的载体旋转与本地化紧密结合……更多的D旋转。因此，类似于锰氧化锰的双交换相互作用的机制正在运行。结果，仅当curie温度相对较高时，仅当载流子密度小于杂质浓度时才能实现铁磁性。 Curie温度即使交换耦合也极大地增加了。我们还研究了光导率。计算的结果表明，当与杂质的耦合增加并在最终频率下出现另一个峰时，电导率的Drude峰会降低，并最终消失。这与实验观察质性一致。直接电导率的结果表明，根据参数的值，尽管我们无法与实验结果达成良好的一致性。2）使用数值模拟，我们检查了由于缺陷而引起的库仑范围的效果，但在最小模型中被假定为接触型。尽管我们无法模拟足够大的系统，但是我们的群集具有100个地点的结果表明，较长范围的范围会导致更广泛的杂质带。结果表明，长期远程的电势导致较高的居里温度。3）我们提出了一类称为“广义局部线图（GPLG）”的晶格结构，在该结构上，紧密结合的谱带结构在其上实现了平坦的带。我们通过使用有限簇的确切对角线化研究了Hubbard模型中的磁性。获得的结果表明，具有GPLG晶格结构的系统是有望实现完整和部分铁磁，铁磁性和抗铁磁性的候选者。较少的