A production method of the present disclosure includes: a first step of preparing a multi-layer graphene, and an iron oxide that is a ferromagnetic material contacting the graphene and containing Fe3O4; and a second step of applying a voltage or a current between the graphene and the iron oxide with an electric potential of the graphene being positive relative to that of the iron oxide, so as to oxidize a part of the graphene or oxidize a part of the graphene and a part of Fe3O4, and thus to form a barrier layer composed of oxidized graphene or of oxidized graphene and Fe2O3 between the graphene and the iron oxide, and thereby forming a spin injection electrode that includes the graphene, the iron oxide, and the barrier layer located at an interface between the graphene and the iron oxide, and that allows spins to be injected into the graphene from the iron oxide via the barrier layer.