  The effect of magnetic STM-tip on electronic, magnetic and electronic
transport properties through the molecule junction STM-tip-Co/CoPc/Co(111), has
been investigated by mean of ab initio electronic structure calculations. The
spin transition has been studied by varying the distance (passing from the
tunneling regime to the contact regime) between the tip and the CoPc molecule
in both configurations, parallel and anti-parallel. Our calculation shows that
the transition of spin of the Co atom of CoPc molecule has led to a change of
the sign of the Magneto-Resistance (MR). It is also shown that the
characteristic I-V has been influenced by this spin-transition of central atom
of CoPc molecule.
