Molecules filtering spins

Using STM with a magnetic tip can be used to probe the magnetic feature of a surface. The tunneling current shall be sensitive to the alignment (collimation) between the spin orientation of the surface and that of the tip. If the tunneling, as is usually the case, is non-magnetic, then parallel alignment yield a bigger current. A very valuable aspect of STM is that this device probes the local properties of a material. This makes it especially useful in investigating defects or impurities of a surface. Now these authors [Phys. Rev. Lett. 105, 066601 (2010)] came to examine what will happen to the signal if the electrons tunnel from the Fe surface into the tip through a single organic molecule with Beneze rings. The result is this: this molecule allows more spin-up electrons to pass. So, it works as a selective valve, which may be tailored to specific applications that needs manipulate spin current. This phenomenon was predicted 3 years ago in Ref.[3], where the computation was implemented in the aid of DFT. However, it may prove more elucidating if a simple model description is prescribed.
For convenience, some references are attested on this subject:

1. Atodiresei, N. et al. Phys. Rev. Lett. 105, 066601 (2010).
2. Brede, J. et al. Phys. Rev. Lett. 105, 047204 (2010).
3. Rocha, A. R. & Sanvito, S. J. Appl. Phys. 101, 09B102 (2007).
4. Barraud, C. et al. Nature Phys. 6, 615–620 (2010).
5. Sanvito, S. Nature Phys. 6, 562–564 (2010).
6. Cinchetti, M. et al. Nature Mater. 8, 115–119 (2009).
7. Drew, A. J. et al. Nature Mater. 8, 109–114 (2009).
8. Szulczewski, G., Sanvito, S. & Coey, J. M. D. Nature Mater. 8, 693–695 (2009)