Spin-polarized transport and the related field of spintronics  rely on lifting of spin degeneracy in various physical properties. A different behavior for “spin up” and “spin down” in metallic magnetic structures has been shown to lead to large magnetoresistive effects which were successfully applied to computer hard drives and nonvolatile magnetic random access memory. On the other hand, recent materials progress in semiconductors has opened a possibility to consider novel effects in spin-polarized transport which could also be useful for spin-based logic. We focus on our proposal for bipolar spintronics in which carriers of both polarities (electrons and holes) contribute to spin-charge coupling. We predict the spin-voltaic effect, a spin-analog of the photo-voltaic effect . The direction of the charge current (which can even flow at no applied bias) can be switched by the reversal of an equilibrium magnetization or of a polarization of the injected spin. The same spin-voltaic effect can also be used to develop a novel class of tunable magnetic transistors.
 I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004).
 I. Zutic, J. Fabian, S. Das Sarma, Phys. Rev. Lett. 88, 066603 (2002); I. Zutic, J. Fabian, S. C. Erwin, Phys. Rev. Lett. 97, 026602 (2006).