Abstract
In this thesis, different fabrication processes were employed to grow Co/Pc(Co on Pc) bilayers structure. Through Magneto Optic Kerr effect (MOKE) and X-ray Photoemission Electron Microscope (X-PEEM), the magnetic responses of ferromagnetic layer deposited on organic semiconductor film were studied. According to the experimental results, Co film depositing on an 8 nm Pc film begins to show its room temperature ferromagnetism at 1.8 nm, along with a complex magnetization patterns. Increasing the thickness of Co film transforms the lateral dimensions and magnetization directions of domains gradually to a larger and better aligned configuration. The coercivity of thick Co film eventually reached a stable value of 13.3 Oe. According to the X-ray Photoemission Spectroscopy (XPS) study reported earlier, the interface of Co/Pc appears to be chemical reacted. In this study, we step further to investigate “where” this chemical reaction is likely to occur through analyzing the spectra of X-ray Absorption Spectroscopy (XAS). Based on the intensity analysis, the Co atoms are suggested to diffuse into Pc layer at the beginning of Co deposition. In order to prevent the occurrence of chemical reaction and diffusion at interface, two methods were adopted - inserting a 2.7 nm Cu layer as the blocking spacer between Pc and Co layers, cooling the substrate during Co deposition. The results show that both approaches can reduce the critical thickness that corresponds to the onset of room temperature ferromagnetism. Since spin transport in a vertical hybrid structure requires the polarized spins to transport through the interface, practical methods capable of reducing the magnetic critical thickness would lower the chance of polarized spins to be scattered (reduce the scattering cross section of polarized spins), and thus help to maintain the spin coherence among carriers.