Controllable spin switch in a single-molecule magnet tunneling junction

A new type of spin-current filter is proposed, which consists of a single-molecule magnet (SMM) coupled to two normal metal electrodes. It is shown that this tunneling junction can generate a highly spin-polarized current, whose spin polarization can be switched by the magnetic field and gate voltage applied to the SMM. Such a spin switching in the SMM tunnel junction arises from the spin-selected single electron resonant tunneling via the lowest unoccupied molecular orbit of the SMM. And the electron current spectrum in absences of external magnetic field is still spin-polarized, which can help us to judge if the molecule’s spin state has reach to the ground-state doublet |±S). This device can be realized with current technologies and may have practical use in spintronics and quantum information.PACS numbers: 72.25.-b, 75.50.Xx, 85.75.-d

Ni(II)porphyrins as pH dependent light-driven coordination-induced spin-state switches (LD-CISSS) in aqueous solution

A water-soluble Ni(II)-porphyrin substituted with a covalently attached azopyridine ligand was synthesized. Upon irradiation with violet and green light, the azo unit performs a reversible cis–trans isomerization. This geometry change triggers a coordination/de-coordination of the pyridine nitrogen at the central nickel(II) ion. The concomitant change in coordination number at the Ni ion in turn switches the spin state between high and low spin, a process we coined a “light-driven coordination-induced spin state switch (LD-CISSS). To increase the coordination power of the pyridine, particularly in aqueous environments, we introduced an electron donating OH group in 4-position. With increasing pH, the hydroxyl group is deprotonated, further enforcing coordination. We report on the properties of this pH-dependent spin switch, particularly the magnetic properties.