As a new generation solid-state memory technology, the Magnetic Radom Access Memory (MRAM) is one of the most promising technologies for data storage, which storages data as a spin state rather than electrical charge. The MRAM technology based on the magnetic tunnel junction (MTJ), consumes less energy and runs faster than the conventional DRAM and SRAM. CoFeB/MgO/CoFeB MTJ is currently used in the STT-MRAM device. CoFeB has high thermal stability, low damping and high tunnel magneto resistance (TMR). The stability of CoFeB is given by the high magnetic anisotropy which is induced by the atomic orbitals of the magnetic layer and the MgO interface. This project will study the domain structure using the wide-field Kerr Microscopy to probe their correlation with atomic level defects in STT-MRAM materials. The project will study systematically the domain structure though the MOKE image and understand better the mechanism of the magnetization switching in the STT-MRAM structure. The different phases of magnetic domain in the CoFeB layers will cause a different switching coercivity and speed. Also the stress and shape effect will induce different coercivity distribution in the whole system which plays an important role in the switching mechanism. The results will be very useful for designing high performance STT-MRAM device. The project will also use Transmission electron microscopy (TEM) to study the switching mechanism of CoFeB MTJ with different material defects condition. The material defect will influence the magnetization switching of the magnetic thin film. With the interface material defect the CoFeB thin film will display different magnetic domain state. This project will provide insights into the designing and fabricating advances STT-RAM device with high capacity and high speed. The project will involve the device modelling, fabrication and characterisation using the state-of-the-art facilities including high quality epitaxy growth, advanced e-beam and focused ion beam lithography, and various structural and properties analysis in the York Laboratory of Spintronics and Nanodevices, the University NanoCenter, and the York-Nanjing Joint Center. This project will be in close collaborations with world leading companies in this area.