Spin-guide source for the generation of highly spin-polarized currents

A ``spin-guide'' source for generation of electric currents with a high degree of spin polarization, which allows long-distance transmission of the spin polarization, is proposed. In the spin-guide scheme, a nonmagnetic conducting channel is interfaced or surrounded by a grounded magnetic shell that transmits electrons with a particular spin direction preferentially, resulting in net polarization of the current flowing through the channel parallel to the interface. It is argued that this method is more effective than spin-filter-like schemes where the current flows perpendicular to the interface between a ferromagnetic metal to a non-magnetic conducting material. Under certain conditions a spin-guide may generate an almost perfectly spin-polarized current, even when the magnetic material used is not fully polarized. The spin guide is predicted to allow the transport of spin polarization over long distances that may exceed significantly the spin-flip length in the channel. In addition, it readily permits detection and control of the spin polarization of the current. The spin guide may be employed for spin-flow manipulations in spintronic devices.