Length-induced large magnetoresistance in polyacene molecular spin valves

Abstract

With the help of first-principles method, an unusual length effect in polyacene molecular spin valves is revealed. It is found that beyond a critical length, the magnitude of tunneling magnetoresistance is significantly enhanced from 10% to 2500%. Theoretical analysis demonstrates that such significant increase of magnetoresistance is related to the nonmagnetic-antiferromagnetic phase transition of polyacene molecules, which is determined by the relative magnetization orientation of the ferromagnetic electrodes. The molecular gap shows distinct length dependence with the change of molecular magnetic state, which keeps decreasing with length in the nonmagnetic state while a fine gap is obtained in the antiferromagnetic state. This work indicates a valid way to obtain considerable tunneling magnetoresistance in long molecular spin valves.