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

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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.