| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 101 === The magnetic tunnelling junction (MTJ) is a sandwiched structure, with //ferromagnetic layer 1 (FM1)/tunnelling barrier (insulator, organic material... etc)/ferromagnetic layer 2 (FM2)//. In MTJs, a pinhole phenomenon may take place in the thin film layer, which is only a few nanometers thick and may be penetrated by other layers, and the pinhole may cause a short circuit. There are many factors influencing the probability of the pinhole, for example: the junction area, growth temperature, deposition pressure and material growth methods and so on. To reduce the problem of pinhole, we adopt nanopore fabrication, which uses electron-beam lithography and the reactive-ion etching method to create a nano-scale bowl-shaped pore with a volcano shaped gate electrode on a 30nm-thick silicon nitride (Si$_{3}$N$_{4}$) membrane. As compare to previous MTJ device, the nanopore type devices still have some transport mechanisms to study.
Giant saturation magnetization (M$_{s}$) materials are used widely in the modern magnetic recording industry and are playing more and more important roles. The well known giant saturation magnetization material Fe$_{65}$Co$_{35}$ alloy can reach 1950 emu/cm$^{3}$. But in recent studies, it has been shown that iron nitride thin films can reach higher saturation magnetization than Fe$_{65}$Co$_{35}$. In this thesis, the iron nitride thin films in bct structure, which may possess high saturation magnetization phase Fe$_{16}$N$_{2}$/ Fe$_{8}$N, are fabricated on GaAs (001) single crystal substrates, buffered by Au (001), which was chosen due to its small lattice mismatch, by reactive DC magnetron sputtering. Different phases of iron nitride were observed by controlling the mixture ratio of Ar and N$_{2}$ in different growth temperature and in-situ post-annealing process. Vibrating sample magnetometer (VSM) and grazing incidence x-ray diffraction (GIXRD) carry out measurements of the magnetic properties and the crystalline structure, and in turn provide a important correlation between magnetism and crystalline structure of FeN system.
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