The investigation of interface properties of FeCo/Bepp2 heterostructures

•The interface between organic Bepp2 and FeCo is important for organic spin-valves.•The interaction at the interface is investigated by XPS and magnetic measurement.•A different fabrication sequence has a different interfacial reaction.•A quite weak interfacial reaction happens when evaporating Bepp2 on FeCo layer.•Ta capping layer is important to prevent the interfacial reaction for Si/FeCo/Bepp2. The interface has become an important issue in organic magnetic spin-valves. In this work, Si/FeCo/Ta, Si/FeCo/Bepp2/Ta, and Si/Bepp2/FeCo/Ta samples with the variation of the FeCo layer thickness were fabricated by direct-current magnetron sputtering for FeCo layers and the thermal evaporation method for Bepp2 layers. The interaction at the interfaces between the FeCo magnetic layer and Bepp2 organic layer was investigated by the traditional magnetic properties measurement and X-ray photoelectron spectroscopy with the Argon ion etching technique. The experimental results show that the interfacial reaction is strong when sputtering FeCo on Bepp2 layer due to the high energy of sputtered FeCo atoms in contrast with the weak interfacial reaction when evaporating Bepp2 on FeCo layer. Moreover, the capping layer of Ta is quite important to protect FeCo layer against oxidation from air either by direct contact or through Bepp2 layer. Our experiment is very helpful for fabricating organic spin-valves with high-spin injection efficiency.