The spin-filter role of the ill-defined layer in FM/Alq3/FM organic spin valve: A first-principle study

• Role of the “ill-defined layer” in Alq3 organic semiconductors is studied.
• Insight into controversial observations on MR in experiments is given.
• Origins of spin polarizations induced by metal penetrations are discussed.

sThe role of the “ill-defined layer” caused by metal penetrations in the Alq3 based organic spin valves is studied using first-principle calculations. Our results indicate that Co and Mn penetrated Alq3 are usually spin-polarized. But, the spin polarization of ill-defined layers formed by Na, Mg, Al, Ga, Sn, and Fe penetration is dependent on the positions of metals in Alq3. An explanation of the effect of the ill-defined layer on spin injection into the Alq3 layer is provided, which gives an insight into the controversial observations on MR in experiments. The present study shows that a spin valve, with Co and Mn (e.g., La0.67Sr0.33MnO3) as magnetic electrodes, is a good candidate in the study of the MR mechanism and spin transport, because the ill-defined layer generated by Co and Mn penetrations can lead to high spin polarization in the Alq3 organic spin valves. Additionally, the origins of spin polarizations induced by different metal penetrations are also discussed.