Interface control of spin transport in magnetic tunnel junctions with MgO\textbackslash Cu-Phthalicyanine hybrid barrier*

In this work, systematic investigation of interface electronic properties in Fe(001)\textbackslash MgO(001)\textbackslash Cu-Phthalocyanine (CuPc) and Fe(001)\textbackslash CuPc was carried out by using spin polarized metastable He de-excitation spectroscopy (SP-MDS) technique. The electronic structure related to the absorption geometry of CuPc on the Fe (001) and MgO(001) was carefully explored. Differences in the spin resolved density of states were observed as a function of CuPc thickness. The clear evidence of spin-polarized organic spinterface appears even at room temperature in ultra-thin (< 2 nm) CuPc films on the epitaxially grown Fe(001)\textbackslash MgO(001) bilayer. These findings have significant implications for understanding of spin injection from a ferromagnetic layer into an organic semiconductor (OSC), and highlight the importance of adsorption geometry and interfacial exchange coupling in the process of spin injection. This is demonstrated in measurements of the spin transport of Fe\textbackslash MgO(001)\textbackslash CuPc\textbackslash Co tunnel junctions. For the MgO\textbackslash CuPC hybrid barrier, high magnetoresistance value ($> 100$\%) and rather small value ($\sim$ 10\%) were measured at 77 K and 300 K, respectively. Our results provide significant new insights into the phenomenon of spin injection into an OSC and the operation of molecular spintronic devices.