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

非线性磁光效应是指二次谐波光的强度或偏振态与磁化强度相关的现象。在大多数块状磁性材料中，由于中心对称的性质，二次谐波产生（SHG）是不允许的。另一方面，在薄膜和超晶格的表面或界面处，由于反转对称性在那里被破缺，所以二次谐波是允许的。在此基础上，我们设计了实验，制备了Fe/Au超晶格和铁磁/金超晶格样品，并对它们的磁光效应进行了研究。半导体异质结构采用脉冲钛蓝宝石激光器作为非线性磁光效应的基本光束，并利用光子计数装置对SH光束进行探测，发现非线性磁光效应对样品的表面条件非常敏感。 关于我们 我们在Fe（15 ML）/Au（15 ML）和Fe（6 ML）/Au（6 ML）超晶格中成功地获得了强而可靠的SH信号。对于Pin-Pout、Pin-Sout、Sin-Pout和Sin-Sout构型，SH信号的非对称性依赖性表现出明确的四重对称模式。非对称花样随磁化强度的变化而出现旋转（或镜面反射），表明超晶格与（100）MgO衬底有良好的外延关系。因为观察到的4重对称性反映了基底的对称性。然而，如果镜面对称保持在表面的平面内，我们永远不能期待四重对称，只要考虑由于电偶极引起的三阶可达性张量。四阶磁化率张量是解释所观察到的奇依赖性所必需的。对于晶体学贡献，应引入电四极子以获得四阶张量，而对于磁性贡献，则需要电偶极子项的磁化展开。|A+Bcos4f+Csin4f| ^2.纵向非线性磁光Kerr旋转可达3度，说明非线性磁光效应为磁性超晶格和异质结构材料的表面和界面研究提供了丰富的信息。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