| Summary: | 碩士 === 國立臺灣師範大學 === 物理學系 === 99 === Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and surface magneto-optical Kerr effect (SMOKE) are used to investigate compositions, surface structure and magnetic properties of ultrathin Fe films on the top of Co-Pt surface alloys. On Co-Pt(111) surface alloys formed at 710 K, as Fe films grow to moderate coverage, the polar Kerr rotation increases and the polar coercive force remains the same as Co-Pt alloy. A Fe/CoPt system shows polar exchange-spring behavior. On Co-Pt(111) surface alloys formed at 550 K, the structure of Fe overlayer also changes and the polar Kerr rotation increase. Due to the lower annealing temperature and the imperfect of CoPt layer, both the coercive force and polar Kerr rotation are smaller as compared to that formed at 710 K. For Fe films on 0.7 ML Co-Pt, the polar exchange-spring magnetic behavior is less pronounced. We infer that both higher annealing temperature and thicker Co-Pt are advantageous for polar exchange-spring. As annealing temperature increases below 800 K for a Fe/Co-Pt system, Fe atoms diffuse into substrate and Co atoms diffuse into the surface. At higher temperatures, both Fe and Co atoms intermix with Pt(111) to form alloy phase. The coercive force for 3 ML Fe/1 ML Co-Pt/Pt(111) is small than that of 3 ML Fe/Pt(111). The additive of Co atoms in Fe-Pt is harmful for the performance as a hard magnet.
Keyword：surface alloy, cobalt, platinum, magnetic properties, exchange-spring magnetic.
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