Effect of Orbital Hybridization on Spin-Polarized Tunneling across Co/C₆₀ Interfaces

The interaction between ferromagnetic surfaces and organic semiconductors leads to the formation of hybrid interfacial states. As a consequence, the local magnetic moment is altered, a hybrid interfacial density of states (DOS) is formed, and spin-dependent shifts of energy levels occur. Here, we show that this hybridization affects spin transport across the interface significantly. We report spin-dependent electronic transport measurements for tunnel junctions comprising C₆₀ molecular thin films grown on top of face-centered-cubic (fcc) epitaxial Co electrodes, an AlO_x tunnel barrier, and an Al counter electrode. Since only one ferromagnetic electrode (Co) is present, spin-polarized transport is due to tunneling anisotropic magnetoresistance (TAMR). An in-plane TAMR ratio of approximately 0.7% has been measured at 5 K under application of a magnetic field of 800 mT. The magnetic switching behavior shows some remarkable features, which are attributed to the rotation of interfacial magnetic moments. This behavior can be ascribed to the magnetic coupling between the Co thin films and the newly formed Co/C₆₀ hybridized interfacial states. Using the Tedrow-Meservey technique, the tunnel spin polarization of the Co/C₆₀ interface was found to be 43%.