SUMMARY
A quantitative study of the influence of substitutional disorder on the transport properties of Fe1-xCox / ?????? / Fe1-xCox magnetic tunnel junctions is presented. From the first principle calculations with taking into account the parameter-free electronic structure it has been found that the substitutional disorder produces a strong effect on the spin-polarized transport in the limit of low concentration of Co in Fe1-xCox alloy, and is negligible when the concentration of cobalt in alloy is larger than 40%. The obtained results are important for understanding the mechanisms responsible for the giant tunneling magnetoresistance.