Electrical Conductivity of Inhomogeneous Systems Application to Magnetic Multilayers and Giant Magnetoresistance

Butler, X.-G. Zhang, and D. M. C. Nicholson Oak Ridge National Laboratory Oak Ridge, TN 37831-6114 

Two recent review articles provide a helpful introduction to the literature on 

Two mechanisms which contribute to GMR have been identified, a non-local mechanism and a quantum mechanism. To understand the first or non-local, mechanism it is necessaiy to understand that on the scale of the electron mean free path (possibly 10 to 20 nanometers at room temperature) electrical conduction is a non-local phenomenon. Electrons may be accelerated by an electric field in one region and contribute to the current in other regions. To a good approximation they may viewed as contributing to the current until they are scattered. 

To a good approximation one can assume that there are two independent groups of electrons (or channels) which carry the current, majority (or spin up) and minority (or spin down). Relativistic effects can couple the electron s spin to its motion through the lattice, but this effect is usually small for the transition metals and has not been included in the calculations shown here. 

Note that because of the different electronic structure for majority and minority Co, the nature of the non-local conductivity is different in the two spin channels. For majority Co, the electronic structure is rather similar to that in Cu, but for minority Co, most of the Fermi energy electrons have low velocities which lead to short mean free paths and hence to localized conductivities, i.e. a strong peak for I=J and a rapid decrease in the conductivity as a function of iI-J.  

ELECTRICAL CONDUCTIVITY OF INHOMOGENEOUS SYSTEMS APPLICATION TO MAGNETIC MULTILAYERS AND GIANT MAGNETORESISTANCE 

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