Spin Valve Behaviors of Cobalt Dioxelene Valence Tautomer Molecular Films*

Cobalt dioxolene complexes exhibit molecular magnetic bistability in the form of valence tautomerism (VT), an intramolecular charge transfer correlated with a spin-crossover, which can be triggered by a variety of external stimuli, including temperature and pressure changes, as well as optical excitation. We present a study of spin valve behaviors in molecular films of a photoswitchable VT sandwiched between ferromagnetic electrodes of permalloy (40 nm) and Co (100 nm) in the form of vertical crossbar stacks. The magnetic switching fields of the spin valves exhibit two sets of values versus temperature and light exposure. The observed bistability correlates with the magnetic states of the VT molecule. In addition, the magnetoresistance of the devices also exhibits a distinct asymmetry depending on the current/voltage bias direction. These findings indicate that molecular bistabilities, e.g. the VT transition, can be utilized to produce new switchable modalities in molecular spintronic devices.