Ultra-thin Films Of Epitaxial Metal Structure And Magnetic Properties Of Regulation

With the development of high density storage, thin films, ultra-thin films and other low-dimensional systems have become new hot topics in magnetism. Those systems show some novel properties, which don't exist in bulk materials. More interestingly, the magnetic properties of low-dimensional systems can be manipulated by preparing special substrates, for example, substrates with different lattice constant or grown with special growth techniques. During my five years' PhD study, my research has mainly focused on characterization and manipulation of novel properties in ultrathin magnetic films. My thesis mainly contains the study of the properties of ultra-thin film, tuning the magnetic anisotropy through lattice wedge and composition wedge substrate.1. We study the capping effect of Au/Fe/GaAs(001) system by using in situ Surface Magneto-optical Kerr effect (SMOKE) and we find that the attenuation of Kerr intensity with increasing thickness of Au is much stronger compared to the calculation result of well-known Zak's theory. By fitting our experimental results, we find that the enhanced absolute value of Voigt constant of Fe ultra-thin films is responsible for the discrepancy between theoretical and experimental results. Furthermore, we give the optimized thickness of Au film as a protection layer, which is 1.4 run.2. We manipulate the anisotropy of Ni by using a lattice wedge substrate. When the lattice constant of the substrate changes from 0.361 nm to 0.373 nm, the critical thickness of the 2nd SRT drops down very fast with the increase of the substrate's lattice constant. At the same time, the critical thickness of the 1st SRT decreases slowly at first and then increases. The turning point is when the substrate's lattice constant is 0.364 nm. The 1st and the 2nd SRT merge together when the substrate's lattice constant is 0.370 nm, above which no polar signal can be detected. We prove that lattice relaxation of Ni film is the main reason for the behavior of the 2nd SRT and the increasing of the 1st SRT. By fitting our experimental results, we believe that the small variation of the 1st SRT in the range between 0.361 nm and 0.364 nm comes from the increasing of the absolute value of surface and interface anisotropy energy density with the increasing of the substrate's lattice constant.3. We use MBE method to deposit 1ML Cu_xAu_1-x on Cu(001). As a result, ordered nano-patterns are observed on the surface. As the content of Cu is decreased, the density of nano-patterns increases. The height of protruding stripe is about 0.015 nm. From the atomic resolved STM, we find that the protruding stripe is formed by two atom lines, without atom sliding on the line. Using Cu_xAu_1-x/Cu(001) as substrate, we grow Ni film on it. We find that the interface anisotropy energy of Ni film is increased by these nano-patterns. Therefore, the critical thickness of the 1st SRT increases with increasing the density of nano-patterns.4. We grow Fe and Cu alloy on Cu(001) with very low Cu content and find that Neel temperature decrease with increasing the content of Cu. By doping Cu into Fe film, the fcc phase can be very stable. In this range, the oscillation can be observed in the range of 4ML—9ML, which is the same with Fe/Cu(001) system. The oscillation, however, cannot be observed anymore with further increasing the film thickness.