Diffusive theory of spin injection is reviewed and a number of new results is
presented for the dc and ac regimes. They were derived by means of the
"gamma-technique" allowing to simplify the calculations by choosing the spin
injection coefficients through different interfaces as the basic variables. The
prospects for increasing spin injection by using resistive spin-selective
contacts are emphasized and spin non-conserving contacts are introduced.
Finding the basic parameters of a junction from the ac data is discussed.Comment: 4 pages, 2 column REVTeX, to be published in Proceedings of Intern.
Symposium on Mesoscopic Superconductivity and Spintronics (Atsugi, March
2002