  Spin Currents in Tunnel Junctions for example induced by thermoelectric
forces due to temperature and magnetization gradients etc. are analyzed. Using
Onsager theory yields directly, in particular for magnetic tunnel junctions,
metallic rings and quantum dots, spin dependently all thermoelectric and
thermomagnetic effects like Seebeck and Peltier ones and Josephson like Spin
currents driven by the phase gradient of the magnetization. The results can be
compared with recent experiments determining the Spin dependent Seebeck effect
and other thermoelectric effects. The Onsager theory can be extended towards an
electronic theory by expressing the Onsager coefficients by current correlation
functions and then calculating these using Lagrange formalism, symmetry and
scaling analysis. Note, Onsager theory can also be applied to spin currents in
molecules and in magnetic ionic liquids.
