Local tunnel spin transport of ballistic electron emission from a tip of a probe microscope

采用等离子体氧化、自由基氧化和自然氧化三种方法制备了低阻铁磁隧道结。Al的厚度为0.6nm - 0.8nm。结的不同初始氧化过程影响结的热处理电学性能。为了制备高质量的结，在单晶Si（111）衬底上生长了以Ag/Cu为缓冲层的下电极。利用扫描隧道显微镜研究了不同氧化方法下的初始氧化过程。经自由基或纯氧氧化的表面为非晶态结构，而经等离子体氧化的表面为晶态Al_2O_3的重构结构。为了深入了解结构对输运性质的影响，制作了弹道电子发射显微镜。利用非弹性电子隧穿谱分析了绝缘层与铁磁电极的界面，得到了绝缘层均匀性所反映的电流图像。谱图在零偏压处有一个尖锐的峰，在20 mV附近有一个宽峰，分别对应于杂质和磁振子散射。少量非磁性材料的插入导致零偏峰的增大和磁振子峰的减小。与外延生长电极的结的光谱显示出低强度的零偏置散射，表明在界面处的杂质的安装的减少。

Ferromagnetic tunnel junctions with low resistance were fabricated using plasma, radical and natural oxidation. The thickness of the Al was 0.6nm - 0.8nm. Different initial oxidation process for the junctions affected the electrical properties on heat treatment of the junctions. In order to prepare the higher quality junctions, the bottom electrode with the buffer of Ag/Cu was grown on a single crystal Si(111) substrate. The junction was appeared to show low bias dependence of tunnel magnetoresistance (TMR) ratio.The initial oxidation process with different oxidation methods was investigated by using a scanning tunnel microscope. The structure was amorphous for the surface oxidized by radical or pure oxygen, while the surface oxidized by plasma was the reconstruction structure of crystal Al_2O_3. For the deep understanding for the structure affecting the transport properties, ballistic electron emission microscope was made. The current image reflected by the homogeneity of the insulator was successfully obtained.The interface between the insulator and the ferromagnetic electrode was analyzed by using inelastic electron tunneling spectroscopy. The spectra showed a sharp peak at zero-bias and a broad peak around 20 mV corresponding to the impurity and magnon scattering, respectively. A little insertion of the non-magnetic materials resulted in the increase of the zero-bias peak and the decrease of the magnon peak. The spectra for the junction with epitaxially grown electrode showed a low intensity of the zero-bias scattering, suggesting of the decrease of the mount of the impurity at the interface.