A novel spin transistor based on spin-filtering in ferromagnetic barriers: a spin-filter transistor

We propose and theoretically analyze a spin-filter transistor (SFT) employing a spin-filter effect in a ferromagnetic barrier layer. The proposed SFT has a tunneling-injection-type hot-electron-transistor structure with a thin ferromagnetic emitter barrier and a thick ferromagnetic collector barrier. The emitter barrier acts as a tunneling-injector of highly spin-polarized hot electrons from the nonmagnetic emitter to the nonmagnetic base, and the collector barrier acts as a spin analyzer that determines the flow of spin-polarized hot electrons from the base to the nonmagnetic collector or to the base electrode. By the combination of these two spin-filters, the output characteristics of the SFT depend on the magnetic configuration (parallel or antiparallel) of the emitter and collector barriers. The SFT can realize not only a very large magnetocurrent ratio, but also current and power gains, which are definitely needed for the design of integrated circuits.