Manipulation of ferromagnetically coupled spin system with light and its applications

(1)研究了氮掺杂对（Ga，Mii）As外延薄膜居里温度Tc的影响。发现了两种影响：第一，由于轻微的晶格收缩而诱发垂直磁各向异性，第二，由于空穴载流子的局部化而降低Tc。成功地开发了提高Mn含量的后退火生长方法，使（In，Mn）As的居里温度达到最高值Tc = 90 K。(2)本文对（Ga，Mri）As的光致磁旋进进行了良好的控制实验和LLG方程分析。很明显，光激发引起了磁各向异性的变化，这导致了有效磁场的变化，从而导致了进动。结果表明，所观察到的现象不是由光诱导的温度升高，而是由光激发引起的。(3)直接观察光致磁化旋转扫描激光磁光显微镜的发展已达到用（Ga，Mn）As测试其性能的阶段。成功地观察到了面内磁化的畴结构。首次实现了圆偏振光诱导的磁化旋转的直接成像。非偏振光没有引起旋转，这强烈表明这种现象不是由样品的光致加热引起的。(4)自旋光伏效应首次成功地研制出具有较大的圆偏振光依赖光电流（>50 nA）的n-AlGaAs/p-InGaAs异质结二极管。利用异质结输运和考虑MCD效应的太阳电池模型进行了理论分析，定量讨论了带边轮廓不连续性的重要性。

(1) Ferromagnetic semiconductorsEffect of nitrogen doping in (Ga,Mii)As epitaxial films was investigated aiming at controlling Curie temperature Tc during the growth process. Two effects were found : firstly, inducement of perpendicular magnetic anisotropy due to a slight lattice shrinkage ; secondly, reduction of Tc due to the localization of hole carriers. The growth method to enhance Mn contents, with post annealing, was developed successfully, which resulted in highest Curie temperature of Tc = 90 K for (In,Mn)As.(2) light-induced precessions of magntizationWell controlled experiments and analysis with LLG equations were carried out to elucidate light-induced precession in (Ga,Mri)As. It became clear that optical excitation induced a change in magnetic anisotropy, which caused a change in an effective magnetic and thus precession. It was concluded that the observed phenomenon is caused not by the light-induced increase in temperate but by the optical excitation.(3) Direct observation of light-induced rotation of magnetizationThe development of scanning laser magneto-optical microscope has reached at the stage of testing its performance with (Ga,Mn)As. Domain structures of the in-plane magnetization was observed successfully. Direct imaging of magnetization rotation induced by circularly-polarized light was achieved for the first time. That unpolarized light did not cause rotation strongly suggested that this phenomenon was not induced by the light-induced heating of samples.(4) Spin photovoltaic effectA n-AlGaAs/p-InGaAs heterostructure diode showing relatively large circularly-polarized-light-dependent photocurrent (>50 nA) was demonstrated successfully for the first time. Theoretical analysis using both heterojunction transport and solar cell model accommodating MCD-effect was also developed, by which importance of discontinuity in band edge profile was discussed quantitatively.