Electronic and magnetic properties of the interface between metal-quinoline molecules and cobalt

Abstract

It was recently established that spin injection from a ferromagnetic metal into an organic semiconductor depends largely on the formation of hybrid interface states. Here we investigate whether the magnetic properties of the interface between cobalt and tris(8-hydroxyquinolinato)-Al(III) (${\text{Alq}}_{3}$), the most prominent molecular candidate for organic spin-valve devices, can be modified by substituting the aluminum atom with either gallium or indium. The electronic structure of ${\text{Alq}}_{3}$, ${\text{Gaq}}_{3}$, and ${\text{Inq}}_{3}$ and the properties of their interfaces with ferromagnetic cobalt are probed experimentally, by using different photoemission spectroscopy methods, and theoretically, through density functional theory calculations. For all cases, the results highlight the presence of spin-polarized interface states. However no striking difference between the properties of the various molecules and interfaces is observed. This is a consequence of the fact that the molecules frontier orbitals are mainly localized on the ligands and they show only a negligible contribution coming from the metal ion.