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

本课题主要完成了三个主要课题：(1)利用MBE技术外延生长包括MnBi在内的优质镍酸锰薄膜；(2)磁性材料纳米制备技术的建立；(3)利用非线性磁光效应观察表面磁性能。具体内容如下：(1)镍酸锰外延生长；纳米结构GaAs衬底上MnAs的MBE生长和掺7% Mn的GaAlAs的MBE生长。MnBi在MgO（001）衬底上以Cu或Au层作为缓冲层进行了MBE生长。这种方法不能成功生长上跖骨。另一方面，通过顺序沉积Mn和Bi制备的种子层上同时蒸发Mn和Bi的通量导致成功的外延生长具有条纹状的RHEED图案。所得薄膜具有垂直的各向异性，磁滞回线具有良好的方形度。磁光研究也进行了…(2)磁性材料的纳米化利用电子束光刻技术制备了嵌入亚微米级磁点阵列：对Si衬底进行图像化处理，形成小于0的点阵列。采用电子束曝光法刻蚀直径为1μm的材料，并采用反应离子刻蚀（RIE）技术刻蚀。将Co金属蒸发填入RIE工艺制备的孔中，再用CMP（化学机械抛光）技术进行抛光，使其表面平整。其次，采用聚焦离子束（FIB）法直接刻蚀磁膜（Co），制备出0.1μm的图案。MFM观察结果与非结构Co膜相同，呈现蛇形图案，说明纳米结构对各向异性没有显著影响。(3)在少数磁性薄膜中观察到非线性磁光效应。在Fe/Au磁性超晶格中，非线性Kerr效应的方位角依赖表现出与相同超晶格中MSHG的方位角依赖相似的明确的四重对称模式。考虑非线性磁化率张量的对称性，对结果进行了成功的分析。在这个项目期间，这三个实验是使用不同的材料独立进行的。用(1)制备的外延MnBi薄膜制备(2)中描述的纳米结构，并在同一样品上用(3)方法观察非线性磁光效应是未来的问题。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