AVS 46th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Wednesday Sessions
       Session MI+EM-WeM

Invited Paper MI+EM-WeM1
Models of Spin-dependent Tunneling

Wednesday, October 27, 1999, 8:20 am, Room 618/619

Session: Spin-Dependent Tunneling and Transport
Presenter: S. Zhang, University of Missouri, Rolla
Correspondent: Click to Email
There are a number of theoretical models of spin-dependent tunneling. Some are based on toy models and others are built on electronic structures of ideal tunnel junctions obtained from ab-initio methods. The question is whether these models are relevant to the experimental realization of the magnetotransport of magnetic tunnel junctions. We analyze these model predictions by taking into account non-ideal nature of the magnetic tunnel junctions studied to date. It is shown that most of the theoretical conclusions are not reliable in interpreting experimental data. There are at least three intrinsic mechanisms on the voltage dependence of magnetoresistance: the effect of electronic structure, inelastic tunnel channels, and spin-dependence of electric field penetrations. The last effect comes from spin-polarized electron screening. When a voltage is applied across a magnetic tunnel junction, charges and spins are accumulated at the interfaces. The conduction electrons tend to screen these charges and spins via Coulomb and exchange interactions; this leads to a spin-dependent voltage absorption by the electrodes. We calculate the voltage dependence of magnetoresistance by including this field penetration effect. When one considers magnetic tunnel junctions beyond simple trilayer structures, e.g., double barrier junctions, a number of additional complications arise. Among them, the energy and spin relaxation of tunnel electrons becomes important. We examine these processes in detail, and present the I-V characteristics and junction magnetoresistance for both two-terminal and three-terminal geometries.