| Summary: | 碩士 === 東海大學 === 物理學系 === 93 === The main purpose of this research is to study the influences of oxygen exposure on the magnetic properties of Co/Ge(111) ultrathin films in the ultra high vacuum (UHV), and this topic has been attacked using surface magneto-optic Kerr effect (SMOKE) technique for magnetic measurement and Auger electron spectroscopy (AES) for compositional analysis. No magnetic hysteresis loop on the polar configuration is found for Co/Ge(111) films with oxygen exposure. On the longitudinal configuration, the coercivity enhances drastically, but the remanence Kerr intensity reduces slightly with increasing the oxygen exposure time. Besides, no exchange bias phenomenon is observed for Co/Ge(111) films with oxygen exposure after cooling in the magnetic field of 400 Oe to 125 K. From Auger electron spectroscopy, it is found that no oxygen adsorption occurs on either Ge(111) surface or CoGe compound interfaces in ultra high vacuum environment. As the thickness of Co films increases above 6 monolayers, pure cobalt islands form on the surface and the amount of oxygen on the surface layers increases with increasing the oxygen exposure time. From the depth profiling measurements, it is shown that oxygen always distributes on the topmost layers of the film, suggesting that oxygen plays a role as a surfactant. The adsorbed oxygen influences the electronic density of states of Co and leads to the changes of the magnetic properties. The appearance of the O/Co/Ge interface could modify the stress anisotropy, resulting in an increase of the coercivity of ultrathin Co/Ge(111) film.
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