Interfacial symmetry of Co-Alq ₃ -Co hybrid structures for effective spin filtering

Understanding the interfacial behavior at FM-OSC-FM hybrid structures for both the bottom contact (Alq ₃ adsorption on Co, Co/Alq ₃ ) and the top contact (Co atop Alq ₃ , Alq ₃ /Co) is crucial for efficient spin filtering with transport of spin-polarized charge carriers through these interfaces. X-ray photoelectron spectroscopy (XPS) spectra indicate a symmetry of charge transfer from Co to Alq ₃ and the corresponding orbital hybridization to a certain extent at both contacts. The alignment of energy levels at both Alq ₃ /Co and Co/Alq ₃ heterostructures is depicted with ultraviolet photoelectron spectroscopy (UPS). Through magnetic images acquired with a X-ray photoemission electron microscope (XPEEM), the strong hybridization of the top contact presents no micromagnetic domain but still shows magnetic coupling, to some extent, to the bottom contact in the Co-Alq ₃ -Co trilayer structure. Measurements of X-ray magnetic circular dichroism (XMCD) demonstrate the induced spin-polarization of non-magnetic Alq ₃ at both contacts, proving Alq ₃ a unique and promising organic material for spin filtering in OSV.