Spinterface between tris(8-hydroxyquinoline)metal(III) molecules and magnetic surfaces: a first-principles study

Using first-principles calculations, we have systematically investigated the hybridization between tris(8-hydroxyquinoline)metal(III) (Mq$_{\mathrm{3}}$, M $=$ Fe, Cr, Al) molecules and magnetic substrates (Co and Cr). Mq$_{\mathrm{3}}$ with different central metal elements but the same organic framework has dramatically different interaction with different magnetic substrates, which affect the interface state significantly. AFM coupling was observed between magnetic Mq$_{\mathrm{3}}$ molecules and ferromagnetic (Co) as well as antiferromagnetic (Cr) substrate, manifested with a superexchange and direct exchange interaction, respectively. Such strong magnetic interfacial coupling may open a gap around the Fermi level and significantly change interface transport properties. Nonmagnetic Alq$_{\mathrm{3}}$ molecule was found to enhance the interface spin polarization due to hybridization between the lowest unoccupied molecular orbitals (LUMO) of Alq$_{\mathrm{3}}$ and metallic surface state. These findings will help better understand spinterface and shed new light on future application of Mq$_{\mathrm{3}}$ molecules in spintronics devices.