Abstract
We investigated two series of ultrathin ferromagnet-organic semiconductor (FM-OSC) hybrid structures fabricated with reversed layer orders in ultra-high vacuum conditions to emulate the interfaces of FM/OSC/FM organic spin-valves. Using X-ray photoemission electron microscopy (PEEM), the magnetic responses of the cobalt (Co) layer in contact with the pentacene (Pc) film were investigated on a microscopic scale. According to the PEEM images acquired on Pc (1.8 nm)/Co bilayers, the Co top layer was found to turn on its ferromagnetic order after its thickness reaches 2.2 nm. Also, upon the onset of magnetic contrast, the element-specific images revealed that the Pc/Co bilayers exhibit a complex domain pattern whose average dimension is at least two orders of magnitude smaller than that of the pattern found in Co (2.4 nm)/Pc bilayers. Further X-ray photoelectron spectroscopy investigations suggest that the magnetic disparities observed between Co/Pc and Pc/Co bilayers are correlated with the different chemistries occurred at their interfaces. © 2011 Elsevier B.V.