Spintronic Spin Accumulation and Thermodynamics

The spin degree of freedom can play an essential role in determining the electrical transport properties of spin-polarized electron systems in metals or semiconductors. In this article, I address the dependence of spin-subsystem chemical potentials on accumulated spin-densities. I discuss both approaches which can be used to measure this fundamental thermodynamic quantity and the microscopic physics which determines its value in several different systems.Comment: 14 pages, 4 figures. Based on lecture given at the XVI Sitges Conference, June 1999. Proceedings to be published by Springer-Verla