  Using first-principles calculations based on density functional theory and
the nonequilibrium Green function formalism, we studied the spin transport
through metal-phthalocyanine (MPc, M=Ni, Fe, Co, Mn, Cr) molecules connected to
aurum nanowire electrodes. We found that the MnPc, FePc, and CrPc molecular
devices exhibit a perfect spin filtering effect compared to CoPc and NiPc.
Moreover, negative differential resistance appears in FePc molecular devices.
The transmission coefficients at different bias voltages were further presented
to understand this phenomenon. These results would be useful in designing
devices for future nanotechnology.
