UC Berkeley

Along the effort of integrating the spin degree of freedom in electronic devices, magnetic structures at the nanometer scale are intensely studied because of their importance in both fundamental research and technological applications. In this dissertation, I present my Ph.D research on several subjects to reflect the broad topics of nanomagnetism research. Single-crystalline, magnetic, ultrathin films are synthesized by Molecular Beam Epitaxy (MBE) and measured by state-of-art techniques such as Magneto-Optic Kerr Effect (MOKE), Photoemission Electron Microscopy (PEEM), X-ray Circular and Linear Dichriosm (XMCD and XMLD) Spectroscopy. First, I will present my work on the quantum well state in metallic thin films. Second, I will present my study on the magnetic long range order in two-dimensional magnetic systems, particularly on the observation of stripe and bubble magnetic phases and the universal laws governing the stripe-to-bubble phase transition. Third, I will present my result on a new type of magnetic anisotropy resulting from the spin frustration at ferromagnetic/antiferromagnetic interfaces. Fourth, I will present our studies on the mechanism of the abnormal interlayer coupling in ferromagnet/antiferomagnet/ferromagnet sandwiches structure. Fifth, I will show a new method to control the oxidation process to realize the control of exchange bias. Sixth, I will revisit the topic of exchange bias and show that the exchange bias actually takes place even before the antiferromagentic spins are frozen. In the last chapter, I will summarize my research and discuss the future of this exciting field.