Room-Temperature Tunnel Magnetoresistance and Spin-Polarized Tunneling through an Organic Semiconductor Barrier

Electron spin-polarized tunneling is observed through an ultrathin layer of the molecular organic semiconductor tris(8-hydroxyquinolinato)aluminum (${\mathrm{Alq}}_3$). Significant tunnel magnetoresistance (TMR) was measured in a $\mathrm{Co}/{\mathrm{Al}}_2{\mathrm{O}}_3/{\mathrm{Alq}}_3/\mathrm{NiFe}$ magnetic tunnel junction at room temperature, which increased when cooled to low temperatures. Tunneling characteristics, such as the current-voltage behavior and temperature and bias dependence of the TMR, show the good quality of the organic tunnel barrier. Spin polarization ($P$) of the tunnel current through the ${\mathrm{Alq}}_3$ layer, directly measured using superconducting Al as the spin detector, shows that minimizing formation of an interfacial dipole layer between the metal electrode and organic barrier significantly improves spin transport.