Cobalt/Fullerene Spinterfaces

Spintronics is a multidisciplinary research field and it explores phenomena that interlink the spin and charge degrees of freedom. The thesis focuses on spin-polarized electronic transports in cobalt (Co) and fullerene (C60) based vertical spintronic devices. It starts with a review about spin-transport phenomena in both inorganic and organic spintronic systems. Some topics, such as, magnetism of electrons, tunneling magnetoresistance (TMR), tunneling anisotropic magnetoresistance (TAMR), antiferromagnetic (AFM) TAMR, spin injection and spin polarization detection via Tedrow-Meservey measurements across ferromagnet-organic hybrid interfaces, and various spin-orbital coupling (SOC) effects, are covered. Chapter 2 contains the experimental studies of the TAMR in spintronic devices consisting of sapphire(substrate)/fcc-Co(8 nm)/AlOx(3.3 nm)/Al(35 nm). The highlights of this project are spin-valve-like magnetic switching behaviour with single ferromagnet fcc-Co, and significant TAMR ratios at 5 K. The effect is primarily governed by the magnetic anisotropic property of the fcc-Co and spin-splitting of surface states via Rashba SOC. The following chapter deals with the tunnel junctions comprising Co and CoO interfaces. Since CoO has the unique AFM property, it shows a significant modification of the spin tunneling phenomena by comparing with the devices without CoO. The Co layer is exchange coupled to the CoO layer and drives rotation of the AFM moments in an external magnetic field. In chapter 4, the organic molecules, C60, with different thicknesses were introduced into the same spintronic devices as they were described in Chapter 2. I have investigated spin-transport across the sapphire(substrate)/Co/AlOx/C60(2 nm to 8 nm)/Al tunnel junctions and concluded the Bychkov-Rashba SOI at different interfaces and resonant tunneling processes can contribute and influence the TAMR. Chapter 5 describes spin transport through Co/C60 hybrid interfaces. I have studied how the interfacial states which are due to the hybridization of Co and C60 impact on spin-transport. The phenomena can be attributed to the magnetic coupling between Co and the newly formed Co/C60 hybrid interfacial states, which is expected to bring some interesting functionalities for organic spintronic applications. A tunnel spin polarization of approximately 43% can be detected using the Tedrow-Meservey method. Chapter 6 provides perspectives for spintronics. Finally, a short summary will be given at the end of the thesis.