Effect of spin excited states on electron transport through an organic ferromagnetic device

Spin excited states in an organic ferromagnet are proposed and investigated on the basis of an extended SSH + Heisenberg (SSH = Su-Schrieffer-Heeger) model. It is found that a spin excited state will form a local distortion of the spin density wave (SDW) of π-electrons while the lattice configuration of main chain has no obvious change. Then the spin-polarized transport properties through an organic ferromagnetic device are investigated with the Landauer-Büttiker formula and Green’s function method. It is obtained that the current will be spin polarized due to the existence of SDW in the ferromagnetic molecule. Both the total current and the spin-polarized current will be modulated when the SDW is excited. The total current through the device is suppressed by the spin excitation of side radicals, through which a conductance switch function may be realized. Compared with ground state, the spin polarization has no obvious change in a low spin excited state and the device still has spin-filter function. Finally, spin excitations induced by temperature is studied and we find that an organic ferromagnetic device can hold a high spin polarization when temperature is not too high.