Revisiting the measurement of the spin relaxation time in graphene-based devices

A long spin relaxation time (tausf) is the key for the applications of graphene to spintronics but the experimental values of tausf have been generally much shorter than expected. We show that the usual determination by the Hanle method underestimates tausf if proper account of the spin absorption by contacts is lacking. By revisiting series of experimental results, we find that the corrected tausf are longer and less dispersed, which leads to a more unified picture of tausf derived from experiments. We also discuss how the correction depends on the parameters of the graphene and contacts.