Charge injection, transport and localization in rubrene

Rubrene crystals bridging a 200–350 nm gap between electrodes made of gold or various ferromagnets (Ni80Fe20, Co90Fe10, Co90Fe10/AlOx) exhibit distinct current:voltage characteristics according to their contact resistance. Fits to the nonlinear characteristics with Ni80Fe20 contacts give a Schottky barrier height of 0.22(1) eV. Only for ohmic contacts with Ni80Fe20 was magnetoresistance observed; it is essentially negative and linear in field, reaching 4% in 5 T at 70 K. The magnetoresistance is tentatively attributed to weak localization. There is no evidence of spin-valve magnetoresistance in the lateral geometry, where the spin diffusion length should be less than 200 nm.