With the implementation of a relativistic Korringa-Kohn-Rostoker Green's function and band-structure method, we analyze the spin-expectation value of the electron states on the Fermi surface of nonmagnetic as well as magnetic metals. It is shown that for relatively light elements such as Cu the spin states are well defined. A separation of all electron states to "up" and "down" spin-polarized states can be done even in the case of quite heavy but monovalent elements such as Au. In contrast, for heavy polyvalent metals such as Pt, the expectation value of the spin operator can be close to zero in large regions of the Fermi surface. In this case the nonrelativistic language of well-defined "spin-up" and "spin-down" states is not valid anymore. For magnetic materials, the relativistic Fermi surfaces change their topology with respect to the nonrelativistic majority and minority sheets because of spin-orbit driven avoided crossings of the bands. As a result, regions with vanishing spin polarization appear.

Ab initio calculations for the tunneling magnetoresistance ͑TMR͒ in planar Fe/ MgO / Fe junctions are presented. The electronic and magnetic structure of the junctions are calculated self-consistently in the framework of density functional theory. The bias dependence of the tunneling conductance and the magnetoresistance is calculated in the limit of coherent tunneling. Positive and negative TMR ratios are obtained as a function of interface structure and even a sign reversal of TMR as a function of bias was found in agreement with experiments.

We present an implementation of the steady state Keldysh approach in a Green's function multiple scattering scheme to calculate the non-equilibrium spin density. This density is used to obtain the spin-transfer torque in junctions showing the magnetoresistance effect. We use our implementation to study the spin-transfer torque in metallic Co/Cu/Co junctions.

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