MBE Growth of MnBi-based Single Crystal and Superlattice Films and Its Characterization by Nonlinear Magneto-Optical Effect

在本项目中，我们完成了以下三个主要课题：(1)用分子束外延技术外延生长包括MnBi在内的高质量的锰系化合物薄膜(2)磁性材料的纳米制备技术的建立(3)用非线性磁光效应观察表面磁性：(1)锰系化合物的外延生长：在纳米结构的GaAs衬底上的分子束外延生长和掺7%Mn的GaAlAs的分子束外延生长。以Cu层或Au层为缓冲层，在MgO(001)衬底上进行了分子束外延生长MnBi.用这种方法不能成功地进行附着体生长。另一方面，在连续沉积Mn和Bi的种子层上同时蒸发Mn和Bi助熔剂可以成功地获得条状RHEED图案的外延生长。得到的薄膜具有垂直各向异性，磁滞回线具有良好的垂直度。还进行了磁光研究…在这部电影中有更多。(2)利用电子束光刻技术制备了磁性材料亚微米磁性点阵嵌入纳米材料：在硅衬底上形成小于0的点阵。电子束曝光直径1μm，反应离子刻蚀(RIE)刻蚀。用蒸发金属填充RIE工艺制备的孔洞，并用化学机械抛光技术将其抛光成平整的表面。然后，用聚焦离子束方法直接刻蚀磁性薄膜(Co)制备0.1μm图形。MFM观察到了与非结构Co薄膜相同的蛇形结构，表明纳米结构对薄膜的各向异性没有显著影响。(3)在少数磁性薄膜中观察到了非线性磁光效应。在Fe/Au磁性超晶格中，非线性克尔效应的方位角依赖关系显示出与同一超晶格中MSHG的方位关系相似的四重对称性。考虑到非线性磁化率张量的对称性，成功地分析了结果。在本项目期间，这三个实验分别使用不同的材料进行。利用由工艺(1)制备的外延MnBi薄膜制备(2)中所述的纳米结构，并利用(3)在同一样品上观察非线性磁光效应是未来的问题。较少

In this project we have finished following three major topics (1) Epitaxial growth of good quality thin films of manganese pnictides including MnBi by MBE technique (2) Establishment of nano-fabrication technology for magnetic materials (3) Observation of surface magnetic properties by nonlinear magneto-optical effectDetails of these topics are described as follows : (1) Epitaxial growth of manganese pnictides : MBE growth of MnAs on nano-structured GaAs substrate and MBE growth of GaAlAs doped with 7% Mn. MBE growth of MnBi on MgO (001) substrate was carried out using Cu or Au layers as a buffer. Eiptaxial growth was unsuccessful by this method. On the other hand, simultaneous evaporation of Mn and Bi fluxes on a seed layer prepared by sequential deposition of Mn and Bi lead to successful epitaxial growth with a streaky RHEED pattern. The obtained film showed a perpendicular anisotropy with a magnetic hysteresis loop of a good squareness. Magneto-optical studies were also carried out … More in this film. (2) Nano-fabrication of magnetic material Embedded arrays of submicron magnetic dots were fabricated by electron-beam lithography technique : Si substrate was patterned to make a dot-array of less than 0. 1μm in diameter by electron beam exposure and was etched by reactive ion etching (RIE) technique. Co metal was evaporated to fill the hole prepared by RIE process and polished to make a flat surface by CMP (chemical mechanical polishing) technique. Next, magnetic films (Co) were etched directly by focused ion beam (FIB) method to fabricate 0.1μm pattern. MFM observation showed snake pattern, the same as that of un-structured Co film, suggesting that the nano-structure made no significant effect on the anisotropy. (3) Nonlinear magneto-optical effect was observed in a few magnetic films. In Fe/Au magnetic superlattices, azimuthal angle dependence of nonlinear Kerr effect showed a well defined four-fold symmetry pattern similar to that observed in the azimuthal dependence of MSHG in the same superlattice. The result was successfully analyzed considering the symmetry properties of nonlinear susceptibility tensor.During the term of this project, these three experiments were carried out independently using the different materials. Fabrication of nano-structures as described in (2) using the epitaxial MnBi film prepared by the process (1) and observation of nonlinear magneto-optical effect by means of (3) on the same sample is a future problem. Less