Characterization of Interfaces in Artificial Superlattice by Means of Nonlinear Magnet-Optical Effect

非线性磁光效应是二次谐波光表现出强度或极化磁化依赖的现象。在大多数块状磁性材料中，由于其中心对称特性，二次谐波是不允许产生的。另一方面，在薄膜和超晶格的表面或界面上，由于逆对称被打破，SHG成为允许的。在本研究中，我们对非线性磁光效应进行了调查研究，从而了解了磁性SHG的宏观和微观成因。在调查工作的基础上，我们策划了实验。对于非线性磁光研究的样品，我们制备了铁/金超晶格和铁磁体/半导体异质结构。本文采用脉冲钛蓝宝石激光器作为非线性磁光效应的基束，并利用光子计数装置对其进行检测。非线性磁光效应对样品的表面条件非常敏感。Fe (IML) /Au （IML）超晶格可能由于表面劣化而无法获得可靠的信号。我们成功地从Fe (15ML) /Au （15ML）和Fe (6ML) /Au （6ML）超晶格中获得了强而可靠的SH信号。在Pin-Pout、Pin-Sout、Sin-Pout和Sin-Sout构型中，SH信号的奇角依赖中发现了定义良好的四重对称模式。奇偶图显示随磁化反转而旋转（或镜像反射）。结果表明，该超晶格与（100）MgO衬底具有良好的外延关系。因为观察到的四重对称反映了衬底的对称性。然而，如果镜面对称仍然存在于表面的平面上，那么由于考虑了电偶极子，我们就无法期望到第三阶磁化率张量的4倍对称。第四阶敏感性张量是解释观察到的奇点依赖性所必需的。对于晶体贡献，应引入电四极体得到四阶张量，而对于磁贡献，则需要电偶极子项的磁化展开。所有这些贡献都被发现提供了| A+Bcos4f+Csin4f | ^2的奇点依赖性。纵向非线性磁光克尔旋转可达3度。说明了非线性磁光效应为研究磁超晶格和异质结构材料的表面和界面提供了丰富的信息。少

Nonlinear magnetooptical effect is a phenonenon in which second harmonic light shows magnetization-dependence of intensity or polarization. In most of bulk magnetic materials second harmonic generation (SHG) is not allowed due to centrosymmetric nature. On the other hand at the surface or the interface of thin films and superlattices SHG becomes allowed since inversion symmetry is broken there.In this study we have made survey studies on nonlinear magnetooptical effect, by which we have gained knowledge on macroscopic and microscopic origins of magnetic SHG.Based on the survey works we planned experiments.For specimens for nonlenear magnetooptical studies we have prepared Fe/Au superlattices and ferromagnet/semiconductor heterostructures. As the fundamental beam for nonlinear magnetooptical effect we adopted a pulsed Ti-sapphire laser and the SH beam was detected by a photon-counting device.Nonlinear magnetooptical effect was found to be very sensitive to surface conditions of samples. … More We could not obtain reliable signal from Fe (IML) /Au (IML) superlattice probably due to surface deterioration.We have succeeded in obtaining strong and reliable SH signals from Fe (15ML) /Au (15ML) as well as Fe (6ML) /Au (6ML) superlattice . Well-defined four-fold symmetry patterns were found in azymuthal anle-dependence of SH signal for Pin-Pout, Pin-Sout, Sin-Pout and Sin-Sout configuration. The azymuthal pattern showed rotaion (or mirror reflection) with the magnetizationrevesal.This result suggests that the superlattice has a good epitaxial relationship with the (100) MgO subsrate. Since the obsered 4-fold symmetry reflects the symmetry of the substrate. However, if mirror symmetry remains in the plane of the surface we can never expec 4-fold symmetry as far as third rank succeptibility tensor due to the electric dipoleis considered . Succeptibility tensor of the fourth rank is necessary to explane the azymuthal dependence observed. For crystallographic contribution the electric quadruploe should be introduced to get rank four tensor, whereas for magnetic contribution magnetization-expansion of electric dipole term is necessary.All of these contribution was found to provide an azymuthal dependence of | A+Bcos4f+Csin4f | ^2.The longitudinal nonlinear magnetooptical Kerr rotation attained as large as 3 degrees.It is thus elucidated that nonlinear magnetooptical effect presents plenty of information for studies of surafces and interfaces of magnetic superlattices and heterostructured materials. Less