Polaron spin filtering in an organic ferromagnetic polymer: a dynamics simulation.

We present a model study of the dynamic properties of a polaron in an organic ferromagnetic polymer by focusing on the spin correlation between the polymer backbone and the side radicals. The simulations are performed by using a tight-binding description coupled with a nonadiabatic dynamics method. We find that, in the presence of an external electric field, the polarons with both up and down spins can get trapped near the side radicals of the polymer chain unless the electric field is stronger than a critical field. However, the magnitudes of the critical electric field vary quite differently for the spin-up and spin-down polarons as a function of the number of side radicals in the polymer, leading to the exponential change of the range of the electric field within which the spin-filtering takes place. The range of the electric field increases nearly in a linear manner with the strength of the electron-lattice coupling as a result of the increase of the polaron binding energy. The impact of the strength of the spin correlation between the backbone and the side radicals on the polaron spin filtering is also discussed. These findings are expected to be useful for the design of organic-based spin filters.