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表现出与磁化强度或偏振有关的现象。在大多数块体磁性材料中，由于中心对称的性质，不允许产生二次谐波。另一方面，在薄膜和超晶格的表面或界面，由于薄膜和超晶格的反转对称性被打破，倍频成为可能。在本研究中，我们对非线性磁光效应进行了调查研究，从而了解了磁性倍频的宏观和微观来源。在我们计划进行实验的基础上，为了进行非线性磁光研究，我们制备了Fe/Au超晶格和铁磁/半导体异质结样品。作为非线性磁光效应的基频光束，我们采用了脉冲钛宝石激光器，并用光子计数装置对SH光束进行了探测，发现非线性磁光效应对样品的表面条件非常敏感。…此外，由于表面的劣化，我们无法从Fe(IML)/Au(IML)超晶格中获得可靠的SH信号，但我们已经成功地从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SH信号的方位依赖关系中，发现了Pin-Pout、Pin-Sout、Sin-Pout和Sin-Sout构型的四重对称型。随着磁化速度的增加，氮化物花样表现为旋转(或镜面反射)，这表明超晶格与(100)MgO亚晶格具有良好的外延关系。因为观察到的4重对称性反映了衬底的对称性。然而，如果在表面平面上保持镜像对称性，我们永远不能排除由于电偶极子而产生的三阶继承张量的四重对称性。四阶的可接受性张量是解释所观察到的氮杂环己酮依赖所必需的。对于晶体贡献，需要引入电四极矩来获得四阶张量，而对于磁贡献，则需要磁化-展开电偶极项。所有这些贡献都提供了|A+BCos4f+Csin4f|^2的共晶依赖关系。纵向非线性磁光Kerr旋转达到3度。从而阐明了非线性磁光效应为研究磁性超晶格和异质材料的表面和界面提供了丰富的信息。较少

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